This PDF file contains the front matter associated with SPIE Proceedings Volume 10680, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The DLR Earth Sensing Imaging Spectrometer (DESIS) is a new space-based hyperspectral instrument developed by DLR and operated under collaboration between the German Aerospace Center (DLR) and Teledyne Brown Engineering (TBE). DESIS will be mounted on the International Space Station on the MUSES platform in 2018 and will provide hyperspectral Earth Observation in the wavelength range from visible to near-infrared with high resolution and near global coverage. TBE provides the platform and infrastructure on the ISS. DLR developed the instrument, while the optical system was fabricated and pre-aligned by the Fraunhofer Institut fur Angewandte Optik und Feinmechanik (IOF). This paper presents the on-ground adjustment, focusing and calibration approach for DESIS done at the optical lab of the Institut fur Optische Sensorsysteme (DLR). The optical lab set-up will be described in detail. Selected calibration results like detector Modulation Transfer Function (MTF) and linearity, optics MTF and wave front, focus position, smile and keystone measurement, instrument spatial and spectral MTF, and absolute radiometric calibration will be presented. The spectral and radiometric in- ight calibration approach of the DESIS calibration unit (CAL) based on stabilized Light Emitting Diode (LED) arrays will be demonstrated. In addition, the innovative pointing unit (POI) in front of the instrument and its pointing accuracy will be introduced. Finally imaging quality and accuracy of the sensor calibration will be evaluated with respect to foreseen applications.

Detection and mapping crack patterns are key issues for structural assessment of concrete structures. The use of image processing for identification of pathologies has undergone major developments, since it is a noninvasive technique providing the precision and reliability required for the task. The authors have developed a method, named SurfCrete, to materials and damages classification on concrete structures, including mapping cracks. This is based on analysis of multi-spectral images, including visible and near infra-red (NIR) regions of the electromagnetic spectrum. Latest improvements include the use of hyperspectral image analysis for crack detection, based on image clustering. The drawbacks of the developed methods are the difficulties usually shown when dealing with surfaces presenting several damages and materials besides cracks, namely due to the presence of biological colonization, repairing mortars, delamination and efflorescence, among other anomalies commonly found on concrete structures. Furthermore, when surfaces are subjected to different light conditions, this also influences the accurate classification of cracks. In this paper, an evolution of the method previously developed, herein named SurfCrete-HSV, is presented. The new method is completely focused on classifying biological colonization based on the classification of HSV false colour images, being therefore more robust and reliable. These HSV images are built from hyperspectral images (wavelengths from 450 nm to 950 nm and 25 nm of bandwidth) by selecting three channels, one from NIR region and two from the visible region of electromagnetic spectrum. The HSV space allows isolating the colour in a single data dimension to enable a brightness free clustering. An image of a concrete specimen with simulation of biological colonization over a smooth surface is used from a database of hyperspectral images, to evaluate SurfCrete-HSV method. Results show that the SurfCrete-HSV method is reliable for detection of biological colonization on concrete surfaces. The best set of channels to use results from combining one from Near Infra-Red with Red and Blue regions of the electromagnetic spectrum, which reveals high accuracy values with acceptable recall.

Inter-pixel crosstalk degrades the point spread function (PSF) of a scientific imager which affects quantitative interpretation of scientific image data. Compared to the CCD, crosstalk is larger in the CMOS image sensor. This problem is challenging due to constant downscaling of the CMOS technology and pixel size. In this work, we parametrized the inter-pixel crosstalk and also modeled it as an empirically quantifiable kernel. A CMOS image sensor with 6 μm pixel pitch is measured. Evidently the crosstalk value can change with the PSF centroid position inside a pixel, primarily due to the spatial extent of the beam, which causes some optical generation in the surrounding pixels. We demonstrate a crosstalk measurement method and its spatial variation with respect to the spot position. This sub-pixel scanning is conducted to measure any crosstalk variation with respect to the sub-pixel spot position. Notable asymmetry on the crosstalk value between rows and columns as well as in the four corners of the POI is observed. This variation shows how the signal is shared at the pixel boundaries. Several POIs (Pixel of interest) over the scan region are measured to analyze the crosstalk variations.

We present a novel multispectral imaging system that measures temperature without knowledge of emissivity. It combines support vector machine regression with low cost PbSe imagers, sensitive in the MWIR range and capable to achieve very high speed acquisition rates with a medium resolution. The system is modular and builds on two or more apertures sensitive to different but close spectral bands. Inspired by the approach adopted by ratio and multi wavelength pyrometers, we estimate temperature from the combined response at these bands. However, we adopt a flexible and transparent approach to modeling multiple regression based on machine learning and using synthetic datasets. We demonstrate high accuracy and robustness against variations in the value of emissivity. Besides a working prototype, our contribution renders a simple procedure for the design of cost effective thermographic systems for field applications demanding reliable measurements in unconstrained conditions.

Carbon nanotubes (CNT) are being intensively studied for many applications because of their unique properties, such as high electrical and thermal conductivities, excellent mechanical and chemical stability. One of the areas of CNT application is a bolometric detection of near- and mid-infrared (IR) radiation. The record near-IR bolometric performance of CNT devices is comparable to the performance of the commercial vanadium oxide detectors [1]. However, the low intrinsic absorption of CNT in the mid-IR range limits their applications for the detection in the crucial 3-5 µm and 8-12 µm regions. The phenomenon of surface plasmon excitation has been utilized to improve light harvesting efficiency of solar cells and to increase absorption of monolayer graphene [2]. Plasmons were recently observed on an individual CNT [3], but the excitation of a surface plasmon on the macroscopic CNT films have not been reported yet. In the study, we experimentally demonstrate the 100%-enhanced bolometric response of a single-walled carbon nanotube (SWCNT) film in the vicinity of a mid-IR surface plasmon resonance. As a basis for the sample we use a pristine SWCNT film with the thickness of 400 nm, the width of 3 mm, and the length of 6 mm, suspended between two gold contacts. The femtosecond laser is used to drill 3- µm round holes which are arranged in a 2D square lattice with a period of 10 µm. Only one half of the film (3x3 mm2) is structured, while the second half is left unstructured to perform reference measurements. Reflectance and transmittance spectra of both parts of the film are measured with the Fourier-transform infrared spectrometer in the range 2-100 µm. Surface plasmon manifests itself as a Fano-type resonance in spectra of the structured part of the film at the wavelengths around 15 µm. The absorption of the structured part is enhanced in the same spectral region by 75% as compared with the unstructured part. Spectral dependence of the bolometric voltage sensitivity is measured using the sample as a detector of the spectrometer. It is shown that the voltage response of the structured part is enhanced in the vicinity of the surface-plasmon resonance by 100%. We show that the wavelength of the resonance and its magnitude can be controlled by tailoring the geometry of the sample. Numerical calculations by scattering-matrix method show that the central wavelength of the absorption resonance can be tuned in the range 5-25 µm. The maximum available enhancement of absorption is 240% as compared with the unstructured film. We claim that the proposed method applies to achieve enhanced spectrally selective response for any CNT-based bolometer in both near- and mid-infrared ranges of the spectrum. [1] G. E. Fernandes, J. H. Kim, A. K. Sood, J. Xu, Adv. Funct. Mater. 2013, 23, 4678. [2] N. K. Emani, T.-F. Chung, A. V Kildishev, et al. Nano Lett. 2013, 14, 78. [3] Z. Shi, X. Hong, H. A. Bechtel, et al. Nat. Photonics 2015, 9, 515

Demand for efficient terahertz radiation detectors resulted in intensive study of the carbon nanostructures as possible solution for that problem. In this work we investigate the response to sub-terahertz radiation of graphene field effect transistors of two configurations. The devices of the first type are based on single layer CVD graphene with asymmetric source and drain (vanadium and gold) contacts and operate as lateral Schottky diodes (LSD). The devices of the second type are made in so-called Dyakonov-Shur configuration in which the radiation is coupled through a spiral antenna to source and top electrodes. We show that at 300 K the LSD detector exhibit the room-temperature responsivity from R = 15 V/W at f= 129 GHz to R = 3 V/W at f = 450 GHz. The DS detector responsivity is markedly lower (2 V/W) and practically frequency independent in the investigated range. We find that at low temperatures (77K) the graphene lateral Schottky diodes responsivity rises with the increasing frequency of the incident sub-THz radiation. We interpret this result as a manifestation of a plasmonic effect in the devices with the relatively long plasmonic wavelengths. The obtained data allows for determination of the most promising directions of development of the technology of nanocarbon structures for the detection of THz radiation.

Fluorescence lifetime determination is widely utilized for bioscience research and analysis. The fluorescence stimulation in conventional systems is usually done with expensive picosecond laser systems. We present a cost-effective 370 nm LED based excitation module and a detection unit based on a Silicon Photomultiplier (SiPM). The functionality of the excitation module as well as the detection module is demonstrated with the fluorescence dye ATTO 390.

For a fast analysis of the fluorescence signal detected by the SiPM, we developed an ASIC for fluorescence histogram recording. The ASIC determines the time between excitation pulse and incoming fluorescence photon with an accuracy of about 80 ps. The ASIC blind time after the excitation pulse is configurable. The determined time is saved in bins. The width of the bins is programmable. Output of the ASIC is a histogram with the counted amount of photons at the different times after excitation. This histogram equals the fluorescence response of the dye. The fluorescence lifetime can be calculated out of this histogram.

Fluorescent lateral flow assays (LFA) strips have gained popularity for medical diagnostics application by offering fast and reliable response in both qualitative and quantitative readout formats. The fluorescence emission is generated when excited with appropriate optical source, and is dependent on the analyte concentration in the sample spotted on the LFA strips. Quantitative detection requires a LFA reader to carry out accurate and precise measurements of the fluorescence emission. These readers can be of either benchtop or handheld type, and conventionally use either photo multiplier tube (PMT) or avalanche photodiodes (APD) or customized photo diodes. In addition to their proven benefits like high sensitivity, speed and gain, the availability of silicon photomultipliers (SiPM) in micro form factor makes them good choice for developing miniaturized LFA strip readers. In this study, a portable fluorescence reader using SiPM sensor has been designed, which records the fluorescence intensity of the spot on planar surfaces e.g. nitrocellulose membrane (NCM) packaged in the plastic cases. The design and operation details of the benchtop reader using SiPM sensor along with excitation source, focusing and collimating optics and power supplies integrated with general purpose microcontroller board in a mechanical housing are reported in this paper. The testing of the developed reader is done by using mercaptopropionic acid capped cadmium telluride quantum dots (MPA-CdTe QDs) as the fluorescent analytes spotted on NCM packaged plastic strips. The results obtained from the developed portable reader are compared with the standard fluorescence plate reader for QD concentration varying from 60 μg/mL to 420 μg/mL and are found to be in good accordance with the response and resolution of the conventional fluorescent plate reader. Further work is under development for testing the developed reader for disease diagnostic applications.

When used as samples cells for optical absorbance measurements, integrating spheres offer increased pathlengths compared to single pass cells combined with tolerance to misalignment. This makes them attractive during alignment of optical instruments and in challenging environments subject to vibration. However, integrating spheres can suffer problems when used in sensitive and / or accurate absorbance measurement. We present our work to date to address these issues in high resolution laser spectroscopy.

Firstly, optical interference effects include both random laser speckle and structured interference fringes created by optical feedback to the laser. Secondly, the sphere’s optical pathlength is a combination of multiple paths that take an exponential pathlength distribution. At low values of absorbance, the measured signal is linear with concentration, but at higher absorbances signals follow a nonlinear but predictable function of absorbance. Thirdly, our most recent work concerns calibration of the optical pathlength, which is a sensitive function of its internal reflectivity. In-situ calibration is needed if the sphere is to be used in dirty environments or with condensing samples. Measurements from multiple independent sources and / or detectors are combined to provide compensation from fouling of the sphere walls and windows.

Results are presented for an integrating sphere used in the measurement of methane. The emission from a tunable DFB laser at 1651nm was tuned across the gas absorption line to measure its concentration. Reduced sphere reflectivity was simulated by applying small areas of black tape on the inner surface. Finally, we give an example of one application where our results are being put into practice: use of an integrating sphere with a tunable laser at 3.3μm to measure atmospheric methane, installed on a two seater light aircraft.

Rephasing the rotational centrifugal effect by laser-induced alignment echoes[1] Dina Rosenberg1,2, Ran Damari1,2, Shimshon Kallush3,4 and Sharly Fleischer1,2 1 Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel 2 Tel-Aviv University Center for Light-Matter Interaction, Tel Aviv 6997801, Israel 3 Department of Physics and Optical Engineering, ORT Braude College, P.O. Box 78, Karmiel 21982, Israel 4 The Fritz Haber Research Center and The Institute of Chemistry, The Hebrew University, Jerusalem 91904, Israel Echo spectroscopy is a central technique in magnetic resonance, electronic and vibrational spectroscopy, enabling researchers to distinguish dynamical dephasing from decoherence phenomena. The interest in echo responses for gas phase rotational spectroscopy is gradually increasing in recent years, with theoretical and experimental results utilizing resonant terahertz fields and non-resonant optical fields to induce a variety of echo responses in multi-level rotational systems. In the talk I will focus on the rephasing property of rotational echoes induced by two ultrashort optical pulses in a gas phase ensemble of molecules. Different from two-level systems associated with a single transition frequency, multilevel rotational systems manifest quantum rotational revivals due to the unique harmonic rotational level spacing. Thus, following their excitation by an ultrashort optical pulse, the molecules demonstrate periodic rotational dynamics with a long series of alignment events persisting under field-free conditions. However, due to the finite rigidity of the molecules (centrifugal distortion) the molecules experience significant dephasing and distortion of the alignment signal with time and the alignment events become gradually longer in duration and with increasing number of oscillations. When applying the second optical pulse after a delay of a few rotational revivals, the accumulated dephasing in the signal is significant and therefore also visible in the echo signal. The first echo signal appears with the same dephasing, only in the reversed phase-time direction. Since the echo manifests the same periodicity as the fundamental revivals, the rephasing its signal occurs gradually in every appearance. When reaching the zero echo signal, at twice the delay between the pulses, the rephasing is complete. Afterwards, the echo signal continues to diphase jointly with the already non-rephasing fundamental revivals. In my talk I will also discuss the dependence of the echo signal on the intensities of the driving pulses and present a quantum-mechanical version of Hahn's famous track-runners analogy to spin echoes [2]. References: [1] D. Rosenberg, R. Damari, S. Kallush, and S. Fleischer, J. Phys. Chem. Lett. 8 ,5128 (2017). [2] E. L. Hahn, “Spin Echoes,” Phys. Rev. 80, 580 (1950).

In the present work, we propose a method to calibrate the instantaneous optical frequency of a tunable laser using frequency comb. The tunable laser is heterodyned with the equally spaced comb lines, and the heterodyne signal then passes through an electronic frequency selection unit. When the optical frequency of the tunable laser is in the vicinity of the comb lines, the output of the frequency selection unit delivers a peak. We analyzed the effect of the characteristics of the narrow bandpass filter (NBF) in the frequency selection unit. Simulated and experimental results show that the characteristic of the output peak is related to the normalized sweeping speed of the input tuning laser source. At small normalized tuning speed, the envelope of the filtered signal follows the amplitude-frequency response characteristic of the NBF. This shows that the filtered signal using Gaussian filter has broader peak than the one using Butterworth filter, due to the slower roll-off behavior in the transition band of Gaussian filters. At large sweeping speed, the envelope of the filtered signal deviates from the amplitude-frequency response character of the NBF. The peak intensity of the filtered signal is attenuated, and the bandwidth of full width at half maximum is broadened. Experiments were carried out to verify the simulated results. In the experiment, the instantaneous frequency of an external cavity laser diode was calibrated using the presented filtering method showing periodic non-linear tuning.

A LED-assisted navigation system for large indoor environments is proposed. White LEDs are used both for illumination purposes and as transmitters. On-off keying modulation scheme is used to broadcast the information together with the identifiers, IDs, related to the physical location of the transmitters. The mobile receiver is implemented using a double p-i-n/pin SiC photodetector with light controlled filtering properties. Coded multiplexing techniques for supporting communications and navigation concomitantly on the same channel are analysed. Fine-grained indoor localization is demonstrated.

Different indoor layouts, using as position technique a four-code assignment for the LEDs, are proposed. Square and hexagon mesh are tested, and a 2D localization design, demonstrated by a prototype implementation, is presented. The key differences between both topologies are discussed. The location and motion information is calculated by position mapping and estimating the location areas along the time. In both topologies, the transmitted data information, indoor position and motion direction of the mobile device are determined.

The results showed that the LED-aided VLC navigation system make possible not only to determine the position of a mobile target inside the unit cell but also in the network and concomitantly to infer the travel direction along the time.

In this research we present a system based on Visible Light Communication (VLC) with the dual purpose of indoor positioning and data transmission. We propose a system based on RGB white LEDs and a pinpin phototetector based on a-SiC:H/a-Si:H to detect the optical signals transmitted y the modulated emitters of the LEDs. A unit navigation cell is defined and characterized by a unique identifier, and the concept is enlarged to adjacent cells. Within each cell, each spatial region is assigned by the optical pattern of the correspondent emitters. Besides, the positioning and navigation functionality, additional data transmission is also demonstrated using four different channels in each navigation cell. A specific codification scheme and decoding algorithm are proposed and discussed. Error control methodology is also presented to enhance the decoding process.

This paper proposes the use of Visible Light Communication (VLC) in Vehicular Communication Systems for vehicle safety applications. A vehicle lighting system that combines the functions of illumination, signaling, communications, and positioning is presented. Using traffic signals, applies the connected vehicle concept to traditional intersections.

A generic model of cooperative transmissions for vehicular communications services is established, which share the common features among diverse vehicular communications scenarios. Three specific vehicular communications are analyzed. One is for Infrastructure-to-Vehicle (I2V) communications from the street lamps, located on roadside, to the vehicles; the other is for in line Vehicle-to-Vehicle (V2V) communications and the last for Vehicle-to-Infrastructure (V2I) communications from cars to the traffic lights, at the crossroad. For the V2V and V2I communication study, the emitter was developed based on the vehicle headlights, whereas for the study of I2V communication system, the emitter was built based on streetlights, whose primary purpose is to provide illumination, and are also used for data communication if modulated at fast rates. The VLC receivers extract the data from the modulated light beam coming from the LEDs emitters. The receivers consist in a double SiC pi’npin photodetector, with light filtering characteristics, located at the rooftop of the vehicle, for I2V communications; at the traffic lights, for V2I; and at the tails, for V2V reception. Clusters of emitters, in a square topology, are used in the I2V transmission. The encoded message contains ID code of each emitter concomitantly with a traffic message that is received, decoded and resent to another vehicle (V2V) or to traffic light, in the crossroad. An algorithm to decode the information at the receivers is established. A phasing traffic flow is presented as a proof of concept. The experimental results, confirmed that the proposed cooperative VLC architecture is suitable for the intended applications.

Gold-coated tilted fiber Bragg gratings (TFBGs) can now be considered as a mature technology for lab-on-fiber sensing based on surface plasmon resonance (SPR) excitation. This sensing architecture brings considerable assets such as easy light injection, temperature fluctuations immunity and remote operation in very small volumes of analytes. Different metal configurations have been used so far, without considerations about their relative performances in terms of surrounding refractive index (SRI) sensing. In this work, we study the impact of the coating on the cladding mode distribution in the TFBG transmitted amplitude spectrum and subsequently on its SRI sensitivity. Different configurations of gold coating are produced and tested, relying on both the sputtering and electroless deposition processes. Interesting spectral features are reported, confirming that the coating thickness and its relative disparity are important design parameters that drive the overall sensing performances.

The applicability of fiber Bragg gratings written in highly birefringent Butterfly micro-structured optical fibers (MSFBG) for simultaneous High Pressure/High Temperature monitoring without a significant pressure/temperature cross sensitivity have recently been shown. This makes these MS-FBG sensors extremely interesting for downhole monitoring in the Oil and Gas industry. However, an important effect to be taken into account for these applications is the presence of hydrogen, as hydrogen is known to diffuse into the fiber structure and therefore might affect the wavelength responses of the sensor element. In this paper, the effect of hydrogen gas on the MS-FBG sensor readings by monitoring the wavelength changes of the MS-FBG sensor in a hydrogen rich environment have been investigated.

In this experiments, two MS-FBG sensors were placed in a hydrogen test chamber: one with its fiber end sealed for pressure sensing and the other with its fiber end kept open for referencing purposes. It could be demonstrated that both sensors show a similar wavelength shift after some time and that due to the hydrogen diffusion, the pressure in the airholes of the sealed MS-FBG sensor equalizes the hydrogen pressure in the chamber. Furthermore, it could be demonstrated that the refractive index seen by the waveguide of the fiber is also affected. Based on all these observations, the influence of the hydrogen on the temperature and pressure measurement performance of the MS-FBG sensor is estimated, and a mitigation scheme that partially compensates for this influence is discussed.

Together with the development of fiber optic sensor networks the accurate and reliable operation of dedicated readout instruments became a critical issue. After years of optimizing the interrogating devices the use of photonic integrated circuits (PICs) has opened a new era of highly reliable, compact and versatile devices offering additionally advantages of low power consumption and cost-optimized design.

Considering the most commonly deployed fiber Bragg grating (FBG) based sensor systems/networks, typically two PICs-based solutions for interrogators may be used: an arrayed waveguide grating (AWG) spectrometer with a broadband SLED source or a set of tunable laser sources with a photodiode detector. Among commercially available PIC technologies the InP platform has a substantial advantage as it allows fabrication of both passive devices (waveguide circuitry) as well as active devices (photodiodes and light sources) in the same technological process.

In this work we investigate two different layouts of AWG-based integrated interrogators fabricated in generic technology of indium phosphide. We analyze the influence of crosstalk between AWG channels on operation of the device and possibility of interrogating narrow-band FBG reflection peaks as well as the influence of input polarization state on the AWG response, which is of fundamental importance for proper operation of an integrated FBG interrogator. As there is no polarization control elements available at present in the offer of generic InP technology providers we discuss the possibility of using off-chip solutions exploiting additional fiber-optic components. As a possible alternative to AWGbased interrogators, we discuss also the possibility of using integrated tunable lasers for FBG interrogation.

The widespread use of smartphones forecasts huge increase in application-based portable sensors, particularly using the embedded light source and camera detector. Albeit Fibre Bragg gratings (FBG) were originally discovered at visible wavelengths, their commercial and scientific dissemination is predominant in the C-band of optical communications. Recently, several authors gave attention to FBG in the visible, aiming simpler and low-costly interrogation methods that could increase the application of FBG sensors in biomedicine, immunology and biophysics. We study the detection of VIS FBG using standard lamps or LEDs coupled to VIS, silicon based, CCDs in commercial instruments. We show that is possible to record the FBG spectrum with adequate signal to noise ratio,allowing hand held FBG interrogation methods in diverse environments.

In this paper, we used the efficient formulation of the approximated transfer matrix model (ATMM) for the analysis of fibre Bragg grating (FBG) sensors’ response under anti-symmetrical strain fields. Exploiting the flexible representation of the transfer matrices in this new model, we will analytically prove that any sort of anti-symmetrical strain distribution over the length of a uniformFBG sensor will result in symmetrical reflected spectra. This phenomenon had been already observed in the literature, but proving it using the classical transfer matrix model was laborious and impractical. The same discussion will be extended to the grating distribution of the FBG sensors as well. A special case of an anti-symmetrical grating distribution could be the linearly chirped FBG sensor (LCFBG), in which the grating distribution is linearly increasing over the length of the FBG. Using computer simulations, it can be seen that such a grating distribution will result in perfectly symmetrical reflected spectra. Therefore, we expect that a well-produced LCFBG, should also have a close to symmetrical reflected spectra, and deviation from this symmetry could possibly indicate undesirable birefringence effects.

We report on the fabrication of an optical, highly-flexible thin film bending sensor which is based on diffused channel waveguide Bragg gratings inscribed into sheets of OrmoStamp hybrid polymers. The inorganic-organic Ormocer thin films are prepared by non-structured UV-enhanced imprint lithography which allows the fabrication of sheet-like slab substrates with a desired thickness. By this approach, 120 μm thin and highly-flexible plane-parallel substrates are achieved. For the inscription of the diffused channel waveguide Bragg gratings, a fast and efficient single writing step concept is applied, which allows the simultaneous inscription of both waveguide and Bragg grating in only a few seconds. The accordingly fabricated waveguide Bragg gratings feature a defined Bragg reflection peak that lies within the telecom wavelength range and is well-suited for sensing applications that require a reliable detection and tracking of the reflected Bragg wavelength. The applicability of the thus achieved devices as highly-flexible thin film bending sensors is investigated by means of deflection measurements. Here, we found a quasi-instantaneous and highly-reproducible response of the diffused channel waveguide Bragg gratings reflected Bragg wavelength to even small deflections which features a linear dependency of 6.05 × 10^-4 nm/μm on the sensors displacement.

We report on the fabrication technology and the application capability of an epoxy polymer based lab-on-a-chip (LOC) concept equipped with integrated Bragg grating sensors allowing for an on-chip temperature referenced refractive index (RI) measurement of fluids. Microfluidic channels as well as optical waveguide structures are fabricated in EpoCore / EpoClad epoxy-based photoresists on a Topas 6017 cyclo olefin copolymer (COC) substrate using multi-mask UV photolithography. Integrated optical sensor elements in terms of Bragg gratings are directly laser-written into the fabricated strip waveguides using the robust phase mask technique with optimized excimer laser parameters.

While the thus produced sensors have turned out to suit well for evanescent refractive index sensing in humidity-saturated environments like aqueous solutions, however, the additional deployment as an independent on-chip fluid temperature sensor is widely restricted due to the considerably temperature-dependent moisture uptake and swelling mechanisms of the epoxy materials, which are comparable to the well-known issues in polymethylmethacrylate. These severe mechanisms prevent the physical quantities temperature and relative humidity from being measured independently. Hence, the presented chip-design demands an extra sensor element solely responding to temperature variations.

In this contribution, we therefore propose and evaluate three differing approaches to realize an enhanced optofluidic labon- a-chip-platform with integrated temperature sensor for a corrected RI measurement using multiple Bragg grating sensors. In the first approach, an EpoCore waveguide Bragg grating sensor is symmetrically sandwiched in between two humidity insensitive Topas 6017 sheets by solvent bonding. In the second method, an amount of COC is fully dissolved in cyclohexane solvent and the liquid copolymer is drop coated onto the sensor area in terms of a thin layer aiming for humidity desensitization. The third approach uses the COC substrate directly itself as temperature sensor material. Thereby, besides the epoxy waveguide grating, a separated further waveguide Bragg grating is laser-written into the Topas substrate material being inherently insensitive to humidity influences.

The aim of this work is to highlight the possibility of local non-intrusive temperature measurements at the interface between a metallic surface and a fluid by analyzing the plasmon resonance on a periodically micro-structured surface. A change in the temperature of the sample surface induces a modification of the local refractive index leading to a shift of the surface plasmon resonance frequency due to interactions between the evanescent electric field and the close environment of the surface. The metallic gratings developed in this study enable a direct excitation of a plasmonic wave, which, in turn, lead to a high sensibility of the local temperature measurement with a very compact and simple device.

The classical method to investigate the activity of the heart is based on the electrocardiogram or ECG which requires to fix pick-ups on the body of the client. If this is not possible an alternative method is the so-called vibrocardiogram or VCG which is the laser signal emitted by a vibrometer and reflected by the body of the client.

Since the VCG is not only influenced by the activity of the heart but also by the movements of the client and his respiration, preprocessing by filtering is required. Furthermore an appropriate location for the measurement of the VCG has to be found. A measure of reliability based on the correlation function of the VCG leads to a useful point of measurement which can be found not only on the thorax close to the heart.

The analysis of the characteristica of the ECG like the heart beat is the basis for a medical diagnosis. The same has to be done with the VCG. One of the goals of the analysis is to detect atrial fibrillation. Whereas the heart beat covers normally the range of 50 to 100 beats per minute in the case of atrial fibrillation the beat might be 300 beats per minute or more. It is shown in this paper that the measure of reliability might not only be used to find the optimal location to measure the VCG but also for the detection of atrial fibrillation.

This method has been derived on the basis of data from clients in a hospital with different heart deseases. The investigations are going on because the new method has not yet reached the level required for clinical application.

The magnetic resonance imaging (MRI) technique is a powerful diagnostic tool which is nowadays commonly used in many fields of medicine. In some cases, especially of the patients of intensive care units, it is highly recommended or even necessary to provide continuous monitoring of basic physiologic parameters, mainly the heart rate and the respiratory rate, during the MRI scan procedure. The presence of a strong magnetic field within the MRI chamber requires application of non-standard devices and solutions. The monitoring system needs to be immune to the strong magnetic field and simultaneously cannot negatively influence on the results of the scan. Therefore, application of optical sensing technologies could be potentially advantageous to fulfil these requirements. In this work we propose a novel optoelectronic measurement system, dedicated to monitoring of the patient during an MRI scan, immune to strong magnetic field and compatible with the MRI apparatus. Fiber Bragg gratings (FBGs) are used as the sensing elements – the strain induced by the patient’s respiration and cardiac activity cause a change of the Bragg wavelength. These changes can be accurately measured and monitored in the time domain. The respiratory and heart rate can be extracted by further processing of the measured signal by dedicated software. The gratings are organized in a network to maximize the effective sensing area. Each of the FBGs has a different Bragg wavelength so that they can be connected in series. The information from the sensors is read out using an interrogator based on an application specific photonic integrated circuit (ASPIC), designed and fabricated in an InP-based generic integration technology. The interrogator comprises a 36-channel arrayed waveguide grating wavelength demultiplexer, which outputs are connected to PIN photodiodes. Such a photonic circuit acts as a spectrometer and allows to reconstruct the reflection spectrum of many gratings simultaneously. An external superluminescent LED is used as the light source, however in the target configuration the source could be monolithically integrated with the interrogator. The Bragg gratings, the interrogator and the SLED are connected with each other using an optical circulator. Initial tests of the monitoring system have been performed using a single fiber Bragg grating as the strain sensor and a commercially available optoelectronic interrogator. The fiber with an inscribed FBG was mounted using an epoxy glue on a PMMA board and deployed under the patient. Two signals can be distinguished out of the measured waves. The first one, with strong and slowly-varying peaks, reflects the respiration of the patient. The second signal, characterized by low-intensity and fast-varying peaks is a result of the cardiac activity. No influence of the magnetic field of the MRI instrument on the sensing system has been observed. The first results have confirmed both the correctness of the approach and the applicability of the system to monitoring the patient’s physical condition during MRI diagnosis. This work was supported by the National Centre for Research and Development, project OPTO-SPARE, grant agreement PBS3/B9/41/2015.

Measurement of carbon dioxide isotopic ratio on a gas sample through Tunable Diode Laser Absorption Spectroscopy over the 2000nm band is a task that poses different kinds of challenges depending on the required resolution or stability. With the particular application of an instrument for the analysis of human breath samples for the diagnosis of Helicobacter Pylori in mind, the performances of such a system have been investigated.

This measurement has to performed before and after ingestion of a test meal and an accuracy within a few parts per mille needs to be reached for a new instrument to be considered as an alternative to the other, more complex and expensive techniques currently used as a diagnostic test.

The considered instrument is based on a 29m Herriott type multi pass cell, direct absorption setup with a VCSEL source and piezoelectric fringe dithering. Effects of temperature and pressure of the sample on line cross sections and broadening are discussed.

The use of a beam splitter and a second photodetector for a live background signal acquisition and spectra normalization was considered and tested against a simpler approach based on only one channel and using more complex fitting techniques to extract the background waveform from the absorption signal itself. For each case, an evaluation of the obtainable performance with different measurement and/or fitting algorithms is presented.

The work has been done with the ultimate goal of measuring small (0.1 liters) samples collected from exhaled breath (usually saturated in water vapor and containing 4 to 10 vol. % carbon dioxide) without any preprocessing other than lowering the measurement cell pressure; for this reason particular attention to isotope ratio measurement stability against variable sample concentration has been put. At the desired accuracy levels, even the differences in collisional broadening coefficients due to gas mixture composition are non negligible; temperature effects can be neglected only by considering proper line pairs for the ratio evaluation.

The current setup shows a resolution of about 0.2% on the δ¹³CO₂ isotopic ratio measurement around the ambient level with a day-to-day reproducibility better than 1.5% on the single channel approach.

Hemolysis is the rupture of the red blood cells (RBCs) with consequent release of hemoglobin to the blood plasma. To detect hemolysis, the red blood cells have to be separated from the blood plasma. Current clinical methods require centrifugation steps for cell/plasma separation, which is time consuming and not suitable for integration into Point-of-Care (PoC) devices. The lack of a fast and reliable PoC hemolysis detection is a central cause of hemolysis being the largest source of unsuitable samples received in clinical laboratories worldwide. Here, we present an optofluidic approach to address this issue. To measure the free hemoglobin in plasma of whole blood, evanescent waveguide absorption is accomplished in wavelength range of 400-430 nm, where hemoglobin has the strongest absorption. For separation of the RBCs, nano-filters are imprinted on top of the waveguide, enabling local blocking of RBCs from the evanescent field region. By this means, our sensor is able to accomplish hemolysis detection on whole blood without any need of sample preparation such as centrifugation. Various nano-imprint techniques are employed to define the gratings couplers (368 nm pitch) and nano-filters(400 nm pitch). The sensor is fabricated on a flexible polymer membrane, enabling easy integration. The nano-imprint fabrication used here allows easy up-scaling for industrial adaption. Furthermore, we use gratings couplers to disperse the guided broadband light and accomplish spectral analysis with a linear camera, which enables highly compact optical setup. We tested the hemolysis sensor integrated in a modified commercial PoC blood gas analyzer. Whole blood and plasma with different free hemoglobin concentrations are tested, proving the filtering ability of the sensor. Detecting interference from other blood proteins such as bilirubin is successfully demonstrated by spectral analysis algorithm. Long-term tests for more than a month further show its high repeatability, specificity, and reliability. We envision large potential in improving PoC blood diagnostic quality by our sensor as well as further applications in optical detection in turbid media.

High-resolution thermal sensing and bioimaging at the cellular level and in animal models is interesting for both early diagnosis and controlled treatment via photothermal conversion of several diseases. Despite excellent in vitro results have been obtained with visible emitting luminescent nanothermometers, their application for in vivo studies is very limited due to the reduced penetration depth of visible light in biological tissues. This can be overcome if materials with emitting in the so-called biological windows (650-1350 nm) are used. Despite all this work, the number of studies exploring the possibilities of longer emission wavelengths in luminescence thermometry are scarce. This includes those lying in the so called short-wavelength infrared (SWIR) that extends from 1.35 to 2.3 μm. SWIR light transmits more effectively (up to three times) through specific biological tissues (oxygenated blood and melanin-containing tumors), achieving higher penetrations depths. Due to the reduced tissue absorbance and scattering within this region. Here, we analyze the possibilities for temperature sensing purposes of emissions in the SWIR region generated by Er³⁺, Tm³⁺ and Ho³⁺ ions in KLu(WO₄)₂ nanoparticles. The thermometric responses of these particles are compared with those shown by other Ln³⁺-doped nanoparticles of the same family of materials operating in the other biological windows, and demonstrate the potentiality of SWIR emitting nanoparticles for temperature measurements in biological tissues. The results indicate that SWIR emitting nanoparticles are good candidates for luminescent thermometry in biomedical applications.

With the increase in complexity of brachytherapy treatments, there is a demand for the development of sophisticated devices for dose delivery verification. An optical fibre sensor for monitoring low dose radiation is presented. The sensor is a Cerium doped Lutetium based scintillation crystal, LYSO (Lu^1.8Y^.2SiO⁵:Ce), provided by Saint-Gobain crystals, which was inserted into a 18G Mick Applicator Needle and coupled to a 1mm plastic optical fibre. The LYSO emits visible light when exposed to low level ionising radiation. The incident level of ionising radiation can be determined by analysing the optical emission. The sensor is designed for in vivo monitoring of the radiation dose during radio-active seed implantation for low dose rate (LDR) brachytherapy, in prostate cancer treatment, providing oncologists with real-time information of the radiation dose to the target area and/or nearby organs at risk (OARs). The radiation from the brachytherapy seeds causes emission of visible light from the scintillation material through the process of radioluminescence, which penetrates the fibre, propagating along the optical fibre for remote detection using a multi-pixel photon counter. The sensor demonstrates a high sensitivity to Iodine-125, the radioactive source most commonly used in brachytherapy. The sensor was initially tested for its response to 0.348mCi of Iodine-125. The sensor was further evaluated for its response to different levels of radiation to determine its suitability in comparison to previous work investigating terbium doped gadolinium oxysulphide (Gd₂O₂S:Tb).

The aim of this study was to investigate the over-response of an inorganic optical fibre sensor (OFS) when measuring percentage depth dose curves (PDDs) with respect to an ion chamber by means of physical measurements and Monte Carlo (MC) simulations. The sensor was constructed by filling a cavity (700 μm diameter and 7 mm deep), which was made in a PMMA (polymethyl methacrylate) plastic optical fibre, with an inorganic scintillating material: terbium doped gadolinium oxysulphide (Gd₂O₂S:Tb). The MC software packages BEAMnrc and DOSXYZnrc were used to develop a MC model of an Elekta Versa HD linear accelerator (linac), which was then used to simulate the Gd₂O₂S:Tb scintillator. The results of the PDD measurements showed a depth dependence of the OFS, however the percentage differences between the ion chamber and the OFS measurements showed that as the radiation field size decreases, the difference between the two measurements decreases from 16.5% to 5.1% for 10x10 cm² and 2x2 cm², respectively. The MC simulation of the sensor showed a good agreement compared to physical measurements at shallow depth in the phantom; however, discrepancies were observed at depth, which was less pronounced for 4x4 cm² than for 10x10 cm². The results of this study indicate that including Cerenkov radiation measurements is essential to accurately quantify the overresponse and the higher discrepancy between the measured and simulated PDD profiles of the OFS.

This paper presents a multi spot projection unit, used in a 3D volume measurement system employed in a heart failure monitoring device, observing the volume of a patient’s feet for symptoms of heart problems (peripheral edema - swelling of the extremities). The stereoscopic image acquisition requires a surface with enough optically detectable texture, usually not present on human skin, which can be resolved by projecting an infrared, static multi-spot optical pattern. The focus of this paper is on creating a very cost-effective, energy efficient, eye-safe projection system, realizing a strongly divergent (up to ±60°) spot pattern, using infrared LEDs and mass fabricable micro-optical elements. Two different setup were tested: a) an LED array combined with a microlens array, and b) a combination of a single LED with a microlens array and a computer generated hologram (CGH) that adds a pseudo-random spot multiplication. For approach a) the microlens array was optimized by ray-tracing. The CGH function for approach b) was found using a wave optical design algorithm (iterative Fourier-Transform Algorithm – IFTA). The micro-lens array master was fabricated by diamondturning, whereas electron-beam lithography was employed for the CGH-master. Both masters were replicated using hotembossing of PMMA. Installed in a prototype of the medical measurement device, the influence on the 3D reconstruction was measured. The proposed solutions allow installing a competitively priced product for automatic peripheral edema monitoring in chronically ill patient homes, which is of great interest for improving their quality of life and the efficiency of their treatment.

Aspergillus is known as one of the most frequent toxigenic fungi in Europe. It produces aflatoxin B1 transformed into aflatoxin M1 (AFM1) present in milk. The International Agency for Research on Cancer (IARC) has included AFM1 in the group I human carcinogens. Acceptable maximum level of AFM1 in milk according to EU regulation is 50 ppt equivalent to 15.2×10-2 nM (the molecular weight of AFM1 is 328.27 g/mol). Up to now, the most used techniques for AFM1 detection in milk are time consuming Enzyme-Linked Immuno-Sorbent Assay (ELISA) and high-performance liquid chromatography associated to fluorescence (HPLC). Silicon photonics based biosensors such as Mach-Zehnder Interferometers and Microring Resonators thanks to their ability to be miniaturize and integrated with electronics and microfluidics in lab-on-a-chip devices, are new candidates to become faster, cheaper and more accurate tools for AFM1 detection in milk. Here, we validate photonic AFM1 biosensors based on an array of four Si3N4 asymmetric Mach-Zehnder Interferometers (aMZI) functionalized by F(ab’)2 fragments and passivated with casein. Analyses of AFM1 binding by Fab’ in MES buffer and in real milk samples, using different concentrations of AFM1, are performed. The dependence of the phase shifts to the AFM1 concentration allows to calculate the association and dissociation rate constants. The proposed biosensor is capable to detect AFM1 concentration down to 50 ppt. For the average dissociation constant (KD) of AFM1-Fab’ interaction, values of (1.8÷5)×10-8 M in MES buffer and 0.8×10-9 M in milk samples are measured. These are in the same order of magnitude as published results. The difference of one order of magnitude between KD in MES buffer and in milk might be caused by the fact that during the preparation of milk samples, an additional concentration of salt is added to the solution which yields a stronger ionic interaction to occur. Finally, the specificity of the interaction is confirmed by using blank solutions that are free from AFM1.

Characterising the amount and the purity of nucleic acid is an important step in state of the art polymerase chain reaction (PCR). In most cases, the analysis is done by stand-alone equipment. For the measurement, a small amount out of the PCR-process has to be removed. Furthermore, the evaluation of the measured spectra occurs only at three wavelengths (230 nm, 260 nm, 280 nm). Therefore, it should be possible to monitor the PCR-process in situ. We demonstrate an illumination unit with three UV-LEDs (245 nm, 265 nm and 280 nm). Every LED is collimated by two lenses. Two longwave-pass filters merge the optical axes of the different wavelength. Lenses and filters are commercial available. The illumination unit is available with and without fiber coupling. The optical behavior of the illumination unit will be shown and discussed. Further, we investigate the observed peak position of the supporting points in dependence of the impurity concentration of an example solution.

In this paper, different guided mode resonance (GMR) grating sensors are studied with the focus on investigating the possibility of high-performance configurations with simplified and potentially low-cost fabrication methods. The gratings are fabricated in polymer using nano-imprint lithography (NIL). We have chosen Ormocer materials, as they allow fabrication at room temperature, are UV patternable and have good optical and dielectric properties. The GMR gratings have a pitch around 550 nm, which corresponds to a resonance response around 850 nm with a Q factor of 2200 in simulations. In experiment, gratings imprinted on glass and on foil are characterized, showing a successful imprinting process of both devices. The measured optical response of the GMR grating for a change of the refractive index unit (RIU) of the cover (Δλ=Δn_c) is 100 nm/RIU. The measured temperature sensitivity is -0.07 nm/K.

A silicon nanowire waveguide based glucose sensor has been proposed and analyzed. It uses minimal invasive approach to measure the glucose level in a very small blood sample, where, Ethylene-diamine-tetraacetic acid (EDTA) as an anticoagulant, sodium fluoride as preservative and blood sample measurand are added in the ratio of 8:1:1. As the glucose concentration in the blood sample varies, the refractive index (RI) of blood changes, accordingly the refractive index of the solution with 10% blood also gets altered, which in turn to deviated response of the biosensor. The prediction of glucose level is affirmed by taking this solution as a cladding measurand of waveguide. Silicon Nanowire Optical Rectangular Waveguide (SNORW) is proposed for the first time in bio-sensing application for the detection of blood glucose. It works on the principle of detecting changes in refractive index for various concentrations of glucose level ranging from 10 mg/dl to 200 mg/dl. Additionally, SNORW sensor characteristics are compared accordingly with the slot waveguide sensors.

In this paper we present the novel compact structure of a multimode interference (MMI) based biosensor. We analyze its working principle, evaluate its expected measurement errors and discuss some possible techniques to reduce them. A full description of phase-error (PE) and cross-talk (CT) for the MMI based biosensor is done. Through simulations we have analyzed the windowing technique and the effect of CCD camera resolution in the reduction of PE and CT. We show that the windowing technique is very effective in reducing PE and CT, where the best results are achieved for the Blackman window with an average improvement coefficient of 1210. The reduction of spectral leakage from this window, due to the high roll-off rate of its side lobs, is dominant against the worse spectral resolution that this window has compared to the others. Increasing the CCD camera resolution from 6 × 10³ pixels/m to 18 × 10³ pixels/m is associated by a rapid reduction of PE and CT with an average improvement coefficient of 44.4. A further increase in the camera resolution is not necessary as it would increase the cost of the device with a very low profit in measurement accuracy.

In this research we apply Laser Induced Breakdown Spectroscopy technique for diagnostics of Diesel Particulate Matter - DPM formed from combustion Diesel engine - exhaust emissions. Particularly we are concern with the measurements of main chemical components of particulate matter, from actual Diesel engine passenger vehicles. Here we analysed DPM from different Diesel engine passenger vehicles of major EU brands car producers used in daily life environment by LIBS technique.

The aim of this study is to reveal the compounds, which are mostly present in the Diesel engine exhaust emissions and can affect the overall composition of the DPM. The presence of these elements in exhaust emission may point to different processes, mainly to fuel quality, insufficient engine combustion process, incomplete catalytic reaction, inefficient Diesel particulate filtering technique, or failure in the Diesel engine.

Due to their high mechanical and corrosion resistance, low signal attenuation, immunity to electromagnetic interferences, optical fibers have demonstrated their high potential in various sensors applications such as health monitoring of structural pieces when they are placed under constrain, vibration or temperature variation. In this paper, we evaluate the capability of a low cost interrogation device, based on the computation on the evolution of the center of mass of interference pattern of a few-mode optical fiber, to detect the presence of a leak around a buried pipeline. The results obtained are in agreement with the theory (nitrogen expanding) and in good relation with other sensors as thermocouples and fiber Bragg gratings.

Polyaniline (PAni), the conducting polymer, has been investigated for decades, and has been explored extensively for electrochemical applications based on the fact that the conductivity and conformation of PAni changes with its protonation-deprotonation effects. We studied a phenomenon, i.e. change in the optical characteristics of PAni without explicit protonation or de-protonation, rather due to interaction of immunoglobulin (IgG) with heavy metal ions on its surface. The present study aims to incorporate PAni as a detection matrix to develop evanescent wave absorbance based fibre-optic sensor for detection of heavy metals in drinking water. Empirical study showed heat treated IgG exhibits more affinity towards heavy metal ions compared to native IgG. Binding of heavy metals (arsenic, lead, mercury and cadmium) to IgG showed spectroscopic alteration of PAni which was utilized to develop a cost-effective fibre-optic heavy metal sensor. The study was accomplished using an experimental set up consisting of a white light source, optical fiber and a spectrometer. The preliminary experiments were carried out with 10 ppb of arsenic, lead, mercury and cadmium and significant response was observed for each of the heavy metals. Interference of the sensor with other normal ions for e.g. potassium, sodium, magnesium, manganese, iron and zinc were also tested. The current investigation represents a significant step to fabricate highly sensitive optical

Distributed acoustic/vibration sensing schemes based on phase-OTDR are naturally sensitive to environmental perturbation. Nevertheless, further sensitivity enhancement is possible by using specialty fibers. In this paper, a nitrogen doped single-mode fiber with increased Rayleigh scattering properties is tested alongside a standard telecommunications single-mode fiber (SMF) for comparative phase-OTDR measurements. The high Rayleigh scattering fiber (HRF) does not only benefit from a higher numerical aperture, but also from a higher non-homogeneity of material density resulting in an enhanced scattering coefficient. For perturbations caused by shaker-induced vibration applied on a fiber section or by an acoustic signal emitted from a loudspeaker, the ability of localizing the perturbation and determining the frequency is studied simultaneously for the HRF and the SMF, using a direct detection phase-OTDR setup. Vibration frequencies in the range 100-7000 Hz with accelerations of up to 0.1g and acoustic signals in the frequency range 100-10000 Hz at sound pressure levels up to 115 dBC are tested. The signal-to-noise ratios (SNRs) for the differential phase-OTDR traces are calculated as the maximum difference signal level in the perturbation zone and a noise reference level outside the zone. Moving average methods are also employed for further enhancement. As expected, the HRF has superior performance for the localization and the frequency characterization, and it allows detection of signal levels that are undetectable with an SMF without using of denoising methods. On average, a 7 dB and a 3 dB improvement can be achieved for vibration detection and acoustic detection, respectively.

There is a set of important selection criteria in the design of fiber optic sensors that determine the compromise between design complexity and performance. Optical fiber sensors not only withstand high temperatures, but they can also operate in different chemical and aqueous media allowing measurements in areas not otherwise accessible. A Fabry-Perot cavity based on an air bubble created in a multimode fiber section is proposed. The air bubble is formed using only cleaving and fusion splicing techniques. The parameters used to produce the microcavities were found empirically. Two different configurations are explored: an inline cavity formed between two sections of MMF, and a fiber tip sensor. In the last, after the air bubble is created, a cleave is made near the cavity, after which the sensor is subjected to several electrical arcs to reshape the cavity and obtain a thin diaphragm. The inline sensor, with a length of ~297 μm, was used to measure strain and presented a sensitivity of 6.48 pm/με. Regarding the fiber tip sensor, it was subjected to glycerin/water mixture variations, by immerging the sensing head in several solutions with different concentrations of water in glycerin. In this case, the sensor had a length of ~167 μm and a diaphragm thickness of ~20 μm. As expected, with the increase of the external medium refractive index, the sensor visibility decreased. Furthermore, a wavelength shift towards red was observed, with a sensitivity of 7.81 pm/%wt. Both devices exhibited low dependence to temperature (<1.8 pm/°C).

For many high-value manufacturing applications, advanced control systems are required to ensure product quality is maintained; this requires accurate data to be collected from in-situ sensors. Making accurate in-situ measurements is challenging due to the aggressive environments found within manufacturing machines and processes. This paper investigates a method to obtain surface profile measurements in a spectral-domain, common-path, low-coherence system. A fibre based Low Coherence Interferometer was built and was used to experimentally measure surface profiles. The fringes obtained from interferograms were transformed into the Fourier domain to obtain a trackable peak relating to the surface depth. This has been illustrated with ideal step height measurements and referenced specimens as well as more challenging surface roughness measurements, which have produced complex signal processing issues. This work opens up avenues for a metrology based system where both machining and measurement system can coexist on the same plane, in aggressive environments.

Fluorescent optical fibers employ the luminescence property of fluorescent dyes in order to radiate light as a response to incident illumination. When multiple dyes are used to dope the fiber, fluorescence results from the energy transfer between the donor and acceptor dyes and the reabsorption process.

In this work we propose a high-resolution distributed optical sensor for position monitoring developed around a yellow fluorescent fiber. Immunity vs. ambient light variations is achieved by employing the spectral behavior of the donoracceptor energy transfer mechanism and the reabsorption process. This consists in a red shift of the fiber emission peaks vs. distance.

Extensive experimentation with the laboratory proof of principle validates the proposed solution. Measurements carried out in laboratory environment under ambient illumination show that the wavelength of the emission peaks is insensitive to the intensity of the incident light, but is dependent on the variation of the ambient light color. Accordingly, rather than monitoring the wavelengths of the emission peaks, the proposed positions sensor evaluates the spectral spacing between the peaks. This provides an accurate estimate of the distance between the fiber end and the incident light application point. The proposed sensor exhibits a monotonous decrease of the spectral spacing vs. distance, which is indeed insensitive to limited variation of the ambient light.

The sensor optimization is devoted to the study of the improvement of the sensor performance (sensitivity, operating interval) as a function of the radius of curvature of the micro-mirrors and the core diameter of the optical fibres. When the mode field diameter of the single mode fibre is smaller, the size of the waist image should have the same value (at a temperature or pressure value) to have a maximum coupling efficiency. During the fluctuation of T or P, the waist size image, which depends on the bend radius of the micro-mirror, scans the mode field diameter of the SMF beyond the Rayleigth range. As a result, the variation in the intensity of the reflected light is relatively faster. So, the slope of the coupling efficiency curve is quite steep. The sensitivity is improved but the range of temperature or pressure variation is shorter. Conversely, if the sizes are relatively large (SMF core as well as waist image), the scanning area is longer, so the sensitivity decreases, but the dynamic range is enlarged. This imposes a choice of detection. The main results and the structure of the sensor will be presented.

Large telescopes use adaptive optics to correct aberrations in wavefronts over large areas. Such aberrations can be measured by a Shack-Hartmann wavefront sensor, an array of individual sensor elements each comprising a micro-lens with a detector at its focal plane. Any phase variation across the wavefront incident upon a sensor element causes the focal spot to move on the detector. The location of the spot therefore provides information about the magnitude and direction of the local tilt in the wavefront at that element. We demonstrate a novel wavefront sensor based on coupling in a multi-core optical fibre. The fibre contains three identical single-mode cores symmetrically positioned at the corners of an equilateral triangle. The fibre is designed to have negligible coupling between the cores, so that their power distribution is faithfully transmitted along the fibre despite any time-varying perturbations. However, the input end of the fibre is locally narrowed down so that the cores couple over 1/4 of a coupling beatlength. This section acts like the lens in a Shack-Hartmann element, in that it converts phase variations at the input (due to wavefront tilt) into intensity variations at the output. Thus sensing of wavefront tilt can be physically remote from detection, in a compact lens-less all-fibre structure. We fabricated a three-core fibre with cores of numerical aperture 0.11, diameter 10 μm and core-to-core centre separation of 40 μm. It was designed so that, for 1550 nm light, less than 0.1% of the light coupled from one core to the others over a length of 150 m. The input section was narrowed over about 40 mm by tapering (ie, heating and stretching) the fibre with an oxy-butane flame. To obtain the required 1/4 beatlength of coupling, we launched 1550 nm light into one core and monitored the outputs in all three as the fibre was elongated. Tapering was stopped when coupled power was maximised, corresponding to 1/2 beatlength of coupling [1]. The narrowed section was then cleaved in the middle, yielding 1/4 beatlength of coupling. To investigate wavefront tilt, the narrowed end of the fibre was mounted in a reflective puck on a mirror mount 7 cm from the end of a single-mode fibre carrying 1550 nm light. This projects a plane wave onto the sensor. The angle and direction of tilt were varied by adjusting the mirror mount, mimicking a perturbation of the plane wavefront. The position of a 635 nm laser beam reflected by the puck onto a screen recorded the angle of tilt. In our preliminary experiments, a range of tilt angles of 2.5 degrees could be measured, along with the direction of the tilt. In due course, we envisage a full wavefront sensor array constructed from a multi-core fibre containing many such groups of three cores, tapered at one end and connected to a remotely-placed sensor array at the other. References [1] R. J., Black et al., Electron. Lett. 22, 1311-1313 (1986)

Measurement of the refractive index and thickness of transparent plates is demonstrated using combined low-coherence interferometry and confocal scanning. The low-coherence measurement provides a quantity related to the group index and the confocal scan provides a parameter related to the phase index. Calculation of both the phase and group indices also requires a measurement of the confocal parameter at multiple wavelengths. This is achieved using a broadband source and a line-scan spectrometer to interrogate different regions of the spectrum. Measurements are made on a range of transparent optical materials with the mean percentage errors of each measurand being 0.08%, 0.06%, and 0.12% for n_p, n_g, and thickness t respectively.

In recent years, whispering gallery mode optical resonators are attracting ever-growing interest of the scientific community. They are axially symmetric dielectric resonators (spherical, disk-like, toroidal, bottlelike etc) with smooth edges that support the existence of whispering gallery modes by total internal reflection on the surface of the resonator. The rotation of the whispering gallery modes resonators with respect to the inertial space causes changes of their radiuses. This, in turn, leads to mutual (same for the opposite directions of the resonator bypass) spectral shift of whispering gallery modes. Thus, the rotation of such resonators causes a spectral shift, registering which one can calculate the motion parameters. Earlier, the prospects of creating an angular velocity sensor based on this effect were considered. Аt the same time the spherical, disk-like and toroidal resonators were considered as sensitive elements of this sensor. This paper is devoted to the analysis of the effect of rotation on the mutual frequency shift of the whispering gallery modes of bottle-shaped resonators. An important aspect of this work is the investigation of the cross-sensitivity to rotation of bottle resonators. The study is based on the results of the simulation in OOFELIEMultiphysics software.

We have studied a structure composed from two wavelength tunable wedged interferometers and proved its potential for providing an increased free spectral range in comparison to a conventional interferential wedge. The interferential wedges with optical thickness from several micrometers to several hundred micrometers and apex angles of the order of tens microradians have been used. We have computed transmission for a monochromatic light beam with arbitrary wavefront using the angular spectrum approach for interferential wedges with different optical thicknesses and apex angles. We have conducted experiments with several stacks formed from different two wedges. Thus, we have confirmed selection of a single transmission resonance within the impact area of a large diameter beam instead of occurrence of multiple transmission peaks observed for a single interferential wedge. The stack enables wavelength tuning for a small diameter multi-wavelength beam in an increased spectral range at keeping high spectral resolution if the structure is formed by a thin and a thick interferential wedges. The experiments have shown that the selected transmission peak is narrowed spatially and spectrally at the expense of lower transmission, which is 50-60% of transmission provided by the used interferential wedges.

We present the results of numerical and experimental study of the photoconductive antennas (PCAs) based on GaAs and its ternary compounds. We produced three photoconductive materials with different indium content, which then were applied for fabrication of the THz PCAs. These PCAs were used as emitters of the THz pulsed spectrometer. We evaluated the stationary transient current generated by the PCAs, simulated their I-V characteristics, and compared them with the experimental ones. Using the finite integration method, we studied the thermal properties of the PCAs and demonstrated significant influence of the heat-sink on the leakage currents of the InGaAs-based PCA. We showed that the heat-sink reduces the operation temperature of the InGaAs-based PCAs by 40-64 % depending on the indium content. The observed results might be interesting for applications of the PCAs in THz pulsed spectroscopy and imaging.

Present work demonstrates the operation of a smartphone platform sensor that accurately measures mercury (Hg (II)) level concentration in water. The sensing principle of the designed sensor is based on the detection of fluorescence emission from a ternary complex containing different concentration of Hg (II) in the mixture. The designed sensor correlates the level of Hg (II) concentration in a given sample through the emission of fluorescence emission from it. Using simple optical components, a compact optical set-up has been designed which can be attached to the rear-camera of the smartphone. Using the designed smartphone sensor Hg (II)-level variation as low as 50ppb can be detected accurately and reliably. The performance of the sensor has been evaluated in presence of other interfering elements such as iron, copper, zinc and manganese and we noticed that the sensor characteristic does not perturb by the presence of such elements. It has been observed that the proposed sensor performs at par with that of a laboratory grad optical spectrometer. Owing to the involvement of low-cost components and user-friendly application that essentially converts the CMOS illumination reading into a readable form we envision that the proposed sensing technique would be useful for in-field based sensing of Hg(II) level in water largely present in industrial waste water and other environmental water bodies.

A spectral interferometric technique to detect the phase shift induced by surface plasmon resonance (SPR) in the Kretschmann configuration is used in sensing small refractive index changes in a liquid analyte. The technique employs a polarimetry setup with an SPR structure comprising an SF10 glass prism, an immersion oil and a gold coated SF10 slide with a adhesion layer of chromium. In this setup two channeled spectra are recorded to detect the spectral phase shift induced by SPR. One spectrum includes reflection of p- and s- polarized waves from the SPR structure for air when the SPR phenomenon does not occur in the source spectral range, and the other one is for an analyte when the SPR phenomenon occurs. The polarimetry setup is employed to measure the spectral phase shift for aqueous solutions of ethanol. In addition, the phase shift is measured at a specific wavelength as a function of the analyte parameter, and the sensitivity is determined. The measurements are accompanied by theoretical modeling of the phase shift induced by SPR using the material dispersion characteristics, i.e., the refractive index dispersions of the SF10 glass, gold, and the analyte.

A theoretical study of a spectral method based on surface plasmon resonance (SPR) to measure the dispersion of a liquid analyte is presented. A setup with an SF10 glass prism and a gold coated SF10 slide is proposed and the SPR phenomenon in the Kretschmann configuration is analyzed in the spectral domain. Using the material dispersion of the SPR structure and the analyte, the resonance wavelength for the ratio of the reflectances of p- and s-polarized waves is determined for different angles of incidence. Using two new procedures, these theoretical values are utilized in obtaining the refractive index of the analyte as a function of the resonance wavelength. The dispersion of the analyte thus retrieved is compared with the one used in the model and it is concluded that one of the procedures is more accurate than the other. The applicability of the new method is demonstrated for two different analytes, water and ethanol, and the measurement range is specified.

In this work, 5-mm long TFBGs were inscribed in photosensitive single-mode optical fiber using the direct writing plane-by-plane femtosecond laser inscription method; a flexible inscription approach that enables absolute control of the grating period, length, angle, width and depth of the grating planes. This new fabrication method brings important differences compared to classical inscription methods. Firstly, these gratings exhibit very low photo-induced birefringence (measured ~8pm) and as we rely on a direct writing process, the tilt angle of the inscribed grating does not affect the Bragg wavelength, allowing for precise positioning. In addition, this method enables the high order grating production, allowing a behavioral study of higher order cladding modes located at lower wavelengths in the 1200 – 1600 nm range. 8th order gratings were produced with cladding and Bragg mode resonances in the C+L bands. The temperature and strain sensitivities were measured for both the Bragg and higher order cladding modes, yielding an exceptional performance. The higher order modes exhibit a negative axial strain, up to -1.99nm (more than two times higher than the standard Bragg peaks) and a solid temperature sensitivity of 10.25 pm/°C : At the same time, for the designed order cladding modes (of the 8th) the refractive index sensitivity is measured at 22 nm/RIU. Keywords:

An effective and sensitive fiber optic surface plasmon resonance based creatinine sensor is presented using molecular imprinting technique. The proposed sensor has a sensitivity of 18.81x10^-2 nm/μM. The limit of detection of the sensor has been found to be 1.17 μM. The selectivity experiments performed with dissimilar analytes confirm the specificity of the sensor for creatine. High sensitivity, low limit of detection, and high selectivity are due to a combined approach of SPR and molecular imprinting techniques. The sensor has numerous other advantages like low cost, ease of handling, capability of online monitoring, and remote sensing.

The study of one-directional dual-wavelength distributed mode-mode fiber interferometer with ability of perturbations localization is presented. The working principle’s feature is based on excited modes quantity increase along the multimode fiber from the launch point to opposite fiber end. In this configuration output signal characteristics depend on amount of modes at the point of lightguide perturbation. In the investigated optical scheme, modes amount is increasing along the fiber at one wavelength and remains unchanged at the other wavelength as a reference. Theoretical consideration and experimental research results are presented.

Surface plasmon resonance (SPR) excitation has been widely studied in the well-known Kretschmann prism configuration, leading to a large variety of refractometric optical sensors. In recent research, this bulky optical device has found a counterpart thanks to the use of metal-coated optical fibers, mainly allowing to considerably reduce the size of the sensors. Some approaches make use of multimode, etched or unclad fibers while the grating- based alternatives are mostly focused on uniform, long period or tilted fiber Bragg gratings (TFBGs). However, plasmonic optical fiber sensing has been pretty much restricted to aqueous solutions due to the remarkable applications of these devices in (bio)chemical sensing. This work gives the roadmap through SPR excitation in air by using a 10° TFBG refractometer. With regard to aforementioned developments, the photo-inscription process is carried out with an excimer laser emitting at 193 nm, which creates the grating planes in a position close to the core-cladding interface. By doing so, it is possible to obtain a cladding mode resonance comb covering the range of the spectrum that corresponds to refractive index values around the one of the air, without the need of using highly tilted FBGs. Indeed, the coupling of cladding modes to the outer medium can be observed in the optical transmitted spectrum of a bare TFBG. In addition, the thickness of the gold thin-film deposited at the grating location is reduced to one third of the one used for SPR excitation in liquids. In this way, all the cladding modes are reflected by the metal when the TFBG is immersed in solution but when it is left in the air a SPR signature appears in the spectrum. The methods described in the present paper are intended to support further developments on plasmonic optical fiber solutions applied to refractive index sensing in gaseous atmospheres.

A preparation of polydimethylsiloxane (PDMS) interferometer located at the end of a single-mode optical fiber is presented. For preparation of Fabry-Perot interferometer (FPI) we used the PDMS Sylgard 184 (Dow Corning). During fabrication process of FPI the length of micro-cavity in PDMS can be set to required size. After the setting the length of microcavity was fixed by encapsulating of another layer of PDMS. By measuring the transmission characteristic under the constant conditions of environments we observe a periodic change of signal depending on the wavelength – interference pattern. When the measurand is applied on FPI, PDMS changes its volume and also its refractive index resulting in a change in length of microcavity. The change of length of FPI modifies the interference pattern. For evaluation of influence of measurands change, we chose one maximum (wavelength of the maximum) as a reference wavelength at the reflected spectra. Then we changed the amount of measurand and we observed wavelength shift of the maximum and compared it with the wavelength of reference maximum of reflected spectra. We investigated the sensitivity of PDMS FPI on temperature and pressure. The dependencies to temperature and pressure have linear character. The temperature sensitivity of fabricated PDMS FPI is 5.76 nm/°C. In free spectral range of FPI it is possible to determine the difference of temperature 2.7 °C. After that 2π jump in reflected spectra occurs. The pressure sensitivity is -0.64 nm/kPa and free spectral range of FPI corresponds to 11 kPa.

In this paper, an opto-mechanical frequency analyzer is designed using micro-optical dielectric resonators based on whispering gallery modes (WGM). Such an optical resonance phenomenon commonly referred to WGM, was excited by evanescently coupling light from a tunable laser diode using a tapered single-mode optical fiber. The proposed design is made from a canonical tube with array of dielectric beams placed inside which made from polydimethylsiloxane (PDMS) with different geometries. Once a sounds source connected from one end of the tube, the standing wave will perturb these polymeric beams. Then, spherical optical polymeric resonators mechanically coupled with the dielectric beams where placed at different locations to measure the acoustic radiation force. High resolution measurements will be achieved due to the high quality factor (Q-factor) of the resonator that can exhibit. Since, the canonical tube will has different resonant frequency at each certain location. The standing wave will perturb the WGM of the sensing element causing a shift in its transmission spectrum. Cross-correlation technique would be used to calculate that shift which called (WGM shifts). An analysis and calibrations are carried out along with preliminary designs and experiments. Results proved that the proposed technique could be used as a very high resolution frequency analyzer with practical success for bio-medical applications. Such a device could be used to split the sound into their component frequency exactly as an optical prism. This was done by creating a sensor that has the same design as the cochlea (inner ear) and placing optical sensors at different locations along the optical-cochlea to be able to detect different frequencies at the same time with high accuracy.

The purpose of this paper is to identify fabrication methods for creating hollow optical whispering gallery modes (WGM) micro-resonators. These resonators are typically made from high optical polymeric materials like polydimethylsiloxane (PDMS) in solid shape which make it work as optical sensors once the round trip of the light is equal multiple integer of the wavelength that we used. The solid WGM resonators proved that it could reach a very high level of sensitivity for a certain input like (electric field, magnetic field and angular velocity,…etc.) but with a low bandwidth; because it behaved as an over damped system. On the other side, theoretically the hollow resonators can get the same level of sensitivity for the same input with an ultra-high bandwidth in kilo Hertz. A lot of sensing applications could be enhanced just using such a proposed sensor. Experimentally, we may consider the hollow resonators as simple harmonic oscillators. Accordingly, two parameters could be adjusted; the stiffness and the mass of the resonator. Since altering the stiffness coefficient requires us to change the material properties of the polymer we use and since there is a lot of constrains on the polymer material that avoid us to deal with it, based on that; changing the mass of the resonator is the only way for increasing its bandwidth. In conclusion, decreasing the mass of the sensor, making it hollow, can significantly affect its mechanical natural frequency leading to increase its bandwidth. Our challenge now is to fabricate these hollow resonators, since its typical size should range between couple of hundreds of micro-meters with fixed wall-thickness to let the optical resonance to occur. Different methods are being tested in this paper and currently we are finding more reliable ways to do it successfully. The first method will be by coating the hollow polymethylmethacrylate (PMMA) sphere with mechanically controlled syringe then a layer of PDMS base would be used as an outer layer which support the optical light to propagate through the resonator. The second method is to use the same hollow sphere but this time with the UV curable PDMS outer layer. The last method when using the microfluidic channels to create the hollow channels to create resonators using the gravitational force and its surface tension. All of these methods to produce these promising micro-optical hollow resonators will be shown with experimental analysis.

Modified optical fiber tips with micrometer/sub micrometer dimensions are very promising in the field of Tip enhanced Raman Scattering (TERS), Surface Enhance Raman Scattering (SERS), optical trapping, plasmonic sensor etc. A unique axicon fabricated on the optical fiber tip by simple chemical etching in 48% Hydrofluoric acid (HF) followed by thin film gold (Au) coating by magnetron sputtering is demonstrated for anti-BSA and BSA binding. The dimension of conical axicon is ~2 μm apex at the core of fiber, opening diameter of ~70 μm at the tip and total length of ~300 μm. The inner surface of the hollow negative axicon is coated with thin film of gold. The dielectric tip experiences notable optical field enhancement due to the plasmonic coating. Further, such tip generates non-diffracting Bessel beam which has several advantages including collimation. To monitor the binding process of protein bovine serum albumin (BSA) and anti-BSA, the tip is processed for anti-BSA binding on the surface of the negative axicon. The tip is further tested to bind BSA of different concentrations. For every change in concentration of the BSA, time response curve with respect to variation in wavelength shift was recorded. The tip has shown sensitivity to protein binding process for BSA concentrations of range 10-12 mg/ml to 10^-4 mg/ml. The sensor saturates for higher concentration of protein BSA around 10^-4 mg/ml. The sensor tends to be very sensitive to proteins of different concentration. This deep seated negative axicon tip based probe can be used for sensing low volumetric bio-samples.

Further development of stochastic aspect of the harmonic signal analysis theory is considered in this article. The choice of the analyzed signal model in the form of a harmonized finite random process is reasoned. It allows to receive the estimation of energy realization of a random process.

The energy spectrum estimations of a random process have been obtained basis on an instantaneous spectrum of the harmonized random process processing. These estimations have been received both in the form of convolution with the Bartlett spectral window and in the form of reference values.

These reference values are obtained by detecting CCD structures in acousto-optic spectrum analyzer and a diffraction grating spectral device, as well as by narrow-band filtering in a multichannel optical spectrometer.

The outstanding role of the optical coherent Fourier processor and the instantaneous spectrum computed with is considered when performing spectral-correlation processing of the signals of the radio and optical bands. Within the framework of the performed studies, the spread functions for "real spectral devices in an ideal implementation" are established. The sampling theorem for the instantaneous spectrum is proved. These general theoretical studies are used to develop the theory of a diffraction grating spectral device of the optical range, as well as an acoustooptic (AO) radio signal analyzer, and the coordinated filter and a correlator of radio signals created on its basis.

An analysis of the spectrum of optical pulses by dispersion-time spectrum analyzer and a diffraction grating spectral device is considered. A theory of the dispersion-time spectrum analyzer of single optical pulses is proposed, which is an optical analog of the dispersion-time method for measuring spectra of radio signals, and the optical fiber is used as the dispersive medium. A computer simulation of the evolution of a monochromatic pulse propagating in a dispersive system in optical fiber is performed, which makes it possible to determine its minimum length and the dynamics of analysis of the instantaneous spectrum of a single optical pulse when the spectrum is measured by a diffraction optical spectral device.

Raman spectroscopy is an optical technique that can be used to evaluate the biomolecular composition of tissue and cell samples in a real-time and non-invasive manner. Subtle differences between datasets of spectra obtained from related cell groups can be identified using multivariate statistical algorithms. Such techniques are highly sensitive to small errors, however, and, therefore, the classification sensitivity of Raman spectroscopy can be significantly impacted by miscalibration of the optical system due to small misalignments of the optical elements and/or variation in ambient temperature. Wavenumber calibration is often achieved by recording the spectrum from a wavenumber reference standard, such as 4-acetamidophenol or benzene, which contains numerous sharp peaks in the fingerprint region. Here, we investigate a commercial polymer slide as a wavenumber reference standard for the calibration of Raman spectra. The Raman spectrum of this slide contains numerous sharp peaks in the fingerprint region. Unlike many other reference standards, the polymer slide is non-hazardous, has an indefinite lifetime, and is designed in the shape of a glass slide used for microscopy. We evaluate this reference in terms of accuracy and repeatability, and we compare with the established 4-Acetamidophenol wavenumber reference.

Doppler Laser Velocity measurement by self-mixing effect using direct modulation laser diode is proposed to distinguish the direction of the object movement. To distinguish the movement direction in conventional way, it is needed to assemble a frequency shift device such as an acoustic optic cell in the optical system. However, the self-mixing scheme cannot satisfy this condition this due to its simple system. Therefore, we applied triangularwave modulation current with repetition frequency of 250Hz directly to the laser diode emitting at a wavelength of 780nm. Target speed of 0.1 - 0.4 cm/s is measured and its movement direction forward and/or backward can be distinguished successfully. Both the velocity and moving direction of the target are obtained.

LIDAR systems are used in many atmospheric research applications. They consist mainly of a transmitting subsystem that emits a pulsed laser beam into the atmosphere and a receiving subsystem for laser backscattered signal detection and analysis. Many of these atmospheric applications requires high accuracy LIDAR systems, which is the focus of this article. In this paper, we provide information on the basic characteristics and performance of a detection chain for a LIDAR system used in remote sensing of the atmosphere. The detection chain, which is characterized by its low-cost and low-power consumption, allows high spatial and temporal resolution, reliable operation and wide dynamic range: A fast, low noise and high efficiency photodetector used in analog mode convert the detected optical backscattered signal into an electrical signal. A wide bandwidth, low noise and low distortion analog variable gain amplifier (DC-300 MHz) amplifies the electrical signal generated by the photodetector before digitization. The variation of the gain of the amplifier makes it possible to obtain a wide dynamic range, which extends over several orders of magnitude (∼10⁵). A fast analog-to-digital converter (ADC 20 MHz digitization rate, 12-bit resolution sampling) that permits a spatial resolution of 7.5 m follows the amplification stage. A high-speed data interface to computer allows fast readout of the acquired signal. Noise and interference, which can affect the performance of the detection chain, will be also discussed.

Optical choppers are applied in a large range of systems, from radiometers and telescopes to spectral and biomedical apparatuses. While classical choppers are built as rotational disks with windows with linear margins (or with oscillatory elements, but also with linear margins to progressively obscure light beams), we have introduced two different types of such devices; (i) eclipse choppers, with disks windows with non-linear margins, oriented outward or inward; (ii) choppers with rotational shafts of different shapes (with slits of various profiles). The former are capable to produce laser impulses with other shapes than classical choppers, while the latter have the potential to achieve much higher chop frequencies than disk choppers in a more compact construct. We have considered in previous studies the typical case of laser beams with circular sections for these choppers. The present study explores a different case, of laser lines being chopped. Geometrical aspects of the obscuration of laser lines considered in different positions – and for different chopper configurations – are discussed. Experiments are carried out to determine the transmission functions for some of the above devices.

Laser radiation scattering in copper-coated silica fibers was investigated by measuring electrical resistance of the metal layer. Scattering coefficients were determined using theoretical model of fiber heating induced by absorption of scattered radiation in the coating. This method can be adopted for direct measurement of fiber laser radiation power.

An autocollimator designed for measuring the three angular coordinates of a rotating object was examined. The impact of the principal primary errors of an autocollimation angular-measurement system on the error in measuring the axis position and magnitude of a rotating object was analyzed. A computer model of an autocollimation system was built based on describing object rotations using quaternions method. The autocollimation measurements algorithms were compared based on the quaternion and matrix models using the autocollimator parameters deviations effect on the total measurement error. Results of experimental research of the two versions of tri-coordinate autocollimation systems were described: one of them used a matrix model and another one – a quaternionic theoretical model. Autocollimator reflectors in the form of two-sided, tetrahedral and pyramidal prisms were investigated and rotation measurement errors were calculated.

Scientific and technological progress of recent years in the production of the light emitting diodes (LEDs) has led to the expansion of areas of their application from the simplest systems to high precision lighting devices used in various fields of human activity. However, development and production (especially mass production) of LED lighting devices are impossible without a thorough analysis of its parameters and characteristics. There are many ways and devices for analysis the spatial, energy and colorimetric parameters of LEDs. The most methods are intended for definition only one parameter (for example, luminous flux) or one characteristic (for example, the angular distribution of energy or the spectral characteristics). Besides, devices used these methods are intended for measuring parameters in only one point or plane. This problem can be solved by using a dome diagnostics system of optical parameters and characteristics of LEDs, developed by specialists of the department OEDS chair of ITMO University in Russia. The paper presents the theoretical aspects of the analysis of LED’s spatial (angular), energy and color parameters by using mentioned of diagnostics system. The article also presents the results of spatial), energy and color parameters measurements of some LEDs brands.

This paper describes diverse schematic configurations serving the optical control of small-amplitude mechanical oscillations’ magnitude. Based on the analysis, it is proposed, that a heterodyned optical reference beam interferometer be used for the control of superficial oscillations, and the acousto-optic light modulator be used to carry out the frequency shift.

A configuration employing this method has been described, with its expected properties analyzed. Characteristics of interference between Gaussian beams has also been studied.

Oxygen saturation levels in blood are usually measured with photoplethysmography (PPG) using two LEDs, one in the red and the other in the near infrared region of the spectrum. A number of studies have increased the number of wavelengths, not only to improve the accuracy of SpO2 measurements, but also to provide real-time measurements of other substances in blood, such as methemoglobin and carboxyhemoglobin. In addition, analysis of PPG signals at different wavelengths could provide information about skin pathologies at various tissue depths. In this work we study the advantages of using photodetection based on vertically stacked double junction photodiodes. The sensitivity of such photodetectors over a wider wavelength range is of particular interest for PPG. We have implemented a test bed, which includes the control of light sources to emulate the transmitted signals, the analog front-end to recover the time multiplexed PPG signals and post-processing to calculate the hemoglobin fractions. We use this framework to compare results of photodetection obtained using a single silicon junction and the combination of a silicon and indium gallium arsenide junction for photodetection.

Optical head with magnetized garnet layer and noble metal grating is modeled. Incident P-polarized light affected by garnet layer changes its polarization due to Faraday effect. We can detect presence or absence of magnetic information after studying changes in polarization of the reflected light. Enhancement of the effect with plasmon resonance is shown.

In the present work, we are demonstrating the capability of making polydimethylsiloxane (PDMS) microsphere sensors, which take advantage of an optical phenomenon called whispering gallery modes (WGM), a resonance condition happened when the optical path length of a laser in a polymeric microsphere is equal to an integer number of wavelengths, to make extraordinary electric field sensors capable of detecting electric fields. These sensors work by measuring the wavelength at which interference due to WGM occurs and then detecting when this value changes due to a change in the morphology of the spheres. This is possible since PDMS microspheres can be made to physically react to external electric fields. This physical reaction is called the electrostriction effect and governed by Navier’s equation for linear elasticity for steady state case. In this paper, an experiment will be conducted to find the angular orientation effects of the electric field on WGM optical sensors. In this experiment, the electric field is supplied by means of brass plates. These plates are mounted on a servo motor to provide the orientation angle of the applied electric field. The microsphere is placed between the plates. Prior to the experiment, the spheres are subjected to a high strength polling electric field of 1 MV/m. Initial results suggests that the sensitivity of the sphere has a dependence on the angular orientation of the sphere in the sensitizing polling electric field with respect to the orientation in the test electric field. This work we will show a definite relationship between the angular orientation in the sensitizing polling electric field and the response in the test electric field in order to maximize sensitivity. This has direct implications on eventual applications, since the orientation of a future sensor package will directly impact the sensitivity and performance of such a sensor used in the neurophotonics applications.

Optical position encoders working according to the interference method consists of a measurement scale and a measuring head moving along each other. The scale has a reflection diffraction grating on its surface and the measuring head has a transmission diffraction grating with same period inside. Laser light passing and diffracting through these two gratings creates an interference signal on an optical detector. Decoding of the interference signal phase allows to determinate current position. Known optical position encoders use complex optical schemes and some phase optical elements to form several quadrature signals with different phase for higher encoder accuracy. Previously we researched such kind of schemes [1, 2]. In this paper we propose to use a common optical scheme without phase elements but with a complex structured measuring head grating for this purpose to simplify an optical scheme and alignment requirements. The optical scheme of position encoder based on measuring head grating with specific structure is research and described in this paper.

The autoreflection systems allows measuring a mirror turning angle as sensitive element in a point of angular deformation with a potential accuracy up to 0.05". Actually the error can exceed considerably the specified value because of existence of systematic error, one of which main components is the error owing to vignetting of a working beam. The component of systematic error due to vignetting of the beam can be eliminated using the compensation algorithm which allows to increase the working distance at the autoreflection measurements. This algorithm bases on vignetting coefficients. In this article we have found the vignetting coefficients using an autoreflection system.

Many areas of optical science and technology require fast and accurate measurement of the radiation wavefront shape. Today there are known a lot of wavefront sensor (WFS) techniques, and their number is growing up. The last years have brought a growing interest in several schematics of WFS, employing the holography principles and holographic optical elements (HOE). Some of these devices are just the improved versions of the standard and most popular Shack-Hartman WFS, while other are based on the intrinsic features of HOE. A holographic mode wavefront sensor is proposed, which makes it possible to measure up to several tens of wavefront modes. The increase in the number of measured modes is implemented using the conversion of a light wave entering the sensor into a wide diffuse light beam, which allows one to record a large number of holograms, each intended for measuring one of the modes

This paper presents the test results of an optical sensor, developed for measuring pressure and temperature in an aircraft fuel pump and tested in a realistic environment at Airbus facilities in Bristol. We demonstrate that optical sensors can survive and operate reliably in harsh conditions.

This work consists on the design and implementation of a compact and accurate biaxial optical fiber sensor (OFS) based on two in-line fiber Bragg gratings (FBGs) for the simultaneous measurement of shear and vertical forces. The two FBGs were inscribed in the same optical fiber and placed individually in two adjacent cavities. In the calibration and performance tests, the response from the optical fiber cells was compared with the values given by a three-axial electronic force sensor. Sensitivity values obtained for the FBG1 are K_1V= (14.15±0.10) pm/N (vertical force) and K_1S= (-26.02±0.08) pm/N (shear force) and for the FBG2 are K_2V= (7.35±0.02) pm/N and K_2S= (-24.29±0.08) pm/N. The conversion of the Bragg wavelength shift, given by the optical fiber sensors, into the shear and vertical force values is also presented along with its comparison to the values retrieved by an electronic sensor, yielding to low RMSE values, which shows the high accuracy of the algorithm applied. This work stands out from the others with optical fiber by the simplicity of its structure. The proposed solution represents a compact and reliable device for simultaneous measurement of shear and vertical forces, useful in several areas, such as: incorporation into insoles for plantar pressure and shear force measurement; electronic skin technologies; smart rehabilitation robotic exoskeletons; or even biomimetic prosthesis.

Self-injection locking, an efficient method to improve the spectral performance of semiconductor lasers without active stabilization, has already demonstrated its high potential for operation with single-longitude-mode fiber lasers. Recently, we have demonstrated significant line-narrowing (more than 1000 times) of the conventional low-cost DFB laser locked to an external fiber optic ring resonator. However, dynamical behavior of such a laser exhibits mode-hopping making its applications for distributed acoustic sensing rather questionable. In order to explore capacity of the injection locked laser for a phase-OTDR, we have designed a simple configuration of the injection locking DFB laser and applied it for detection and localization of perturbations with a phase-OTDR based distributed vibration sensor. The conventional DFB laser locked at critical coupling regime through fiber optic ring resonator of 3.75 m length (Free Spectral Range is 54.5 MHz) delivers CW mode-hoping free radiation with a linewidth of about ~5.0 kHz, i.e. ~200 times narrower than the linewidth of free-running laser. In combination with the moving differential processing algorithm such a laser is capable to provide high SNR distributed measurements of vibrations and dynamic strain perturbations. The fiber under test comprises three sections of standard single mode fiber, with a total length of ~4.5 km. Perturbations have been locally implemented into the test fiber at two positions using a shaker and a piezoelectric stretcher, respectively. In the first case, perturbations of the fiber induced by the shaker at a frequency of 815 Hz have been recognized as a peak in the recorded and processed traces with a signalto- noise ratio (SNR) of 12 dB over a 10 m resolution cell. In the second case, dynamical strain induced by the fiber stretcher over 40 m at a frequency of 3 kHz is shown in a similar pronounced peak with a signal-to-noise ratio (SNR) of 11 dB. These signatures are similar to the results obtained with a commercial 1 kHz linewidth laser employed with the same phase- OTDR setup. We believe that proposed solution could be a basis for development of a cost-effective phase-sensitive OTDR for distributed sensing specified for the distance up to tens of kilometers.

In this work a heterogeneously integrated germanium (Ge) NIR photo-resistor fabricated on CMOS-compatible silicon substrates is presented. The resistor is fabricated on an epitaxial germanium films grown on silicon using a novel liquid phase crystallization (LPC) process. First, silicon wafers were coated with amorphous germanium deposited using PECVD. Next, Ge film is crystallized into epitaxial germanium using a thermal anneal cycle during which Ge undergoes melting and controlled cooling. The LPE Ge films is polycrystalline but epitaxial with threading dislocation density of ~10⁹ cm^-2. On the LPE germanium, NIR photo-resistors were fabricated with metal-semiconductor-metal (MSM) inter-digitated structure with an active area of 150 μm x 300 μm. Responsivity of the devices was characterized using a fiber laser, tunable from 1500 to 1600 nm. With 1550 nm excitation, a photocurrent of 100 μA was measured at a bias of 4V with laser power of 25 mW, corresponding to a responsivity of 4 mA/W.