This PDF file contains the front matter associated with SPIE Proceedings Volume 9274, including the Title Page, Copyright information, Table of Contents, Authors, Introduction (if any), and Conference Committee listing.

Optical sensors can be used to measure various quantities such as pressure, strain, temperature, refractive index, pH value and biochemical reactions. The interrogation of the sensor can be performed spectrally or using a simple power measurement. However, the evaluation of the sensor signal and the subsequent radio transmission of the results is complicated and costly. A sophisticated system setup comprising a huge number of electrooptical components as well as a complete radio module is required. This is not only expensive and unreliable but also impractical within harsh environment, in limited space and in inaccessible areas. Radio-over-Fiber (RoF) technology implies signals modulated on an electrical carrier being transmitted over fiber by using optical carriers. Combining RoF techniques and optical sensors, a new class of measurement devices readable by a radio interfaces is introduced in this paper. These sensors use a modulated input signal generated by a RoF transmitter that { after being influenced by the optical sensor--is directly converted into a radio signal and transmitted. This approach enables remote read-outs of the sensor by means of wireless evaluation. Thus, costly, voluminous, power hungry and sensitive equipment in the vicinity of the measurement location is avoided. The equipment can be concentrated in a central location supporting existing radio transmission schemes (e.g. WiFi).

Two novel magnetooptic sensors are proposed which are based on mutual compensation of external field-induced linear or circular birefringence. One is based on mutual compensation of the external field-induced linear birefringence produced by both magnetooptic Cotton-Mouton effect and electrooptic Kerr effect. The other one is based on mutual compensation of the external field-induced circular birefringence in crystals exhibiting both Faraday magnetooptic effect and electrogyration effect, such as lead molybdate (PbMoO₄) crystal. The 50Hz ac magnetic field in the range of 167Gs was measured by means of electrogyration compensation. Compensating voltage was about 16.5V/Gs for single lead molybdate crystal with a length of 5mm along its principal optical axis. The two proposed magnetooptic sensors can be used in the closed-loop measurement of magnetic field.

We develop a hybrid wavelength division multiplexing optical fiber network with distributed fiber-optic sensors and quasi-distributed FBG sensor arrays which detect vibrations, temperatures and strains at the same time. The network has the ability to locate the failure sites automatically designated as self-diagnosis and make protective switching to reestablish sensing service designated as self-healing by cooperative work of software and hardware. The processes above are accomplished by master-slave processors with the help of optical and wireless telemetry signals. All the sensing and optical telemetry signals transmit in the same fiber either working fiber or backup fiber. We take wavelength 1450nm as downstream signal and wavelength 1350nm as upstream signal to control the network in normal circumstances, both signals are sent by a light emitting node of the corresponding processor. There is also a continuous laser wavelength 1310nm sent by each node and received by next node on both working and backup fibers to monitor their healthy states, but it does not carry any message like telemetry signals do. When fibers of two sensor units are completely damaged, the master processor will lose the communication with the node between the damaged ones.However we install RF module in each node to solve the possible problem. Finally, the whole network state is transmitted to host computer by master processor. Operator could know and control the network by human-machine interface if needed.

We present a long-range high spatial resolution optical frequency-domain reflectometry (OFDR) based on optimized deskew filter method. In proposed method, the frequency tuning nonlinear phase obtained from an auxiliary interferometer is used to compensate the nonlinear phase of the beating signals generated from a main OFDR interferometer using a deskew filter. The method can be applied for the entire spatial domain of the OFDR signals at once with a high computational efficiency. In addition, we apply the methods of higher orders of Taylor expansion and cepstrum analysis to improve the estimation accuracy of nonlinear phase. We experimentally achieve a measurement range of 80 km and a spatial resolution of 20 cm and 80 cm at distances of 10 km and 80 km that is about 187 times enhancement when compared with that of the same OFDR trace without nonlinearity compensation. The improved performance of the OFDR with the high spatial resolution, long measurement range and short process time will lead to practical applications in real-time monitoring and measurement of the optical fiber communication and sensing systems.

We propose and fabricate a new type fiber acoustic sensor based on dual fiber Bragg gratings (FBGs) configuration. The acoustic sensor head is constructed by putting the sensing cells enclosed in an aluminum cylinder space built by two Cband FBGs and a titanium diaphragm of 50 um thickness. One end of each FBG is longitudinally adhered to the diaphragm by UV glue. Both of the two FBGs are employed for reflecting light. The dual FBGs play roles not only as signal transmission system but also as sensing component, and they demodulate each other’s optical signal mutually during the measurement. Both of the two FBGs are pre-strained and the output optical power experiences fluctuation in a linear relationship along with a variation of axial strain and surrounding acoustic interference. So a precise approach to measure the frequency and sound pressure of the acoustic disturbance is achieved. Experiments are performed and results show that a relatively flat frequency response in a range from 200 Hz to 1 kHz with the average signal-to-noise ratio (SNR) above 21 dB is obtained. The maximum sound pressure sensitivity of 11.35mV/Pa is achieved with the Rsquared value of 0.99131 when the sound pressure in the range of 87.7-106.6dB. It has potential applications in low frequency signal detection. Owing to its direct self-demodulation method, the sensing system reveals the advantages of easy to demodulate, good temperature stability and measurement reliability. Besides, performance of the proposed sensor could be improved by optimizing the parameters of the sensor, especially the diaphragm.

An intensity demodulated strain sensing scheme based on multiple phase-shifted fiber Bragg grating (FBG) is investigated. Wavelength shifts related to the external strain signal will result in various power change received by the photodetector. The reflected spectrum of the sensing multiple phase-shifted FBG are designed using the transfer matrix method to and fabricated by dithering phase mask method. The strain sensing scheme is analyzed numerically by relate the power change to reflectivity spectrum, thus help us optimize the design and fabrication of multiple phase-shifted FBG to achieve maximum sensitivity. The experimental results show that the strain sensitivity can be significantly enhanced by over 10dB by using phase-shifted FBG with many phase shifts compared to a normal FBG.

Broadband-trimming band-rejection filters based on chirped and tilted fiber Bragg gratings (CTFBG) are proposed and experimentally demonstrated. The flexible chirp-rate and wide tilt-angle provide the gratings with broadband filtering functions over a large range of bandwidth (from 10 nm to 150 nm), together with a low transmission loss (less than 1 dB) and a negligible back-reflection (lower than 20 dB). The slope profile of CTFBG in transmission can be easily tailored by adjusting the tilt angle, grating irradiation time and chirp rate-grating factor, and it is insensitive to polarization of launch condition. Furthermore, by coating the CTFBG with a suitable polymer (whose refractive index is close to that of the cladding glass), the cladding modes no longer form weakly discrete resonances and leave a smoothly varying attenuation spectrum for high-quality band rejection filters, edge filters and gain equalizers.

Structural health monitoring has become more and more popular in application of damage diagnosis and safety assessment. Optical fiber sensors, as one of the most efficient sensing elements, for the superior advantages of long-term stability and durability, good geometrical shape-versatility, corrosion resistance and anti-electromagnetic interference, are widely used in diverse technological fields. Measurement precision of the sensor is thus emphasized and strain transfer analysis put forward to explain the action mechanism and improve the test accuracy. Theoretical derivation on strain transfer error analysis of optical fiber sensor applied to structure with local debonding interface is carried out in this paper. Cases that optical fiber sensors are bonded on the surface of structure and embedded in structure are discussed, respectively, and related error modification functions are provided. The research is meaningful for improving the precision of optical fiber sensors applied to structures with the existing of local debonding interface, which will be ultimately serve for showing true mechanical state of structures.

The safety of under-water risers in drilling platform is of great significance. A packaged fiber Bragg grating (FBG) sensor for real-time stress monitoring is designed for the applications on oil drilling risers under 3000 meters deep water. A copper tube which is the main component of the sensor has a small hole along its axes and a groove at its each end. The bare FBG is passed through the small hole and fixed to its ends by epoxy resin. Then the copper tube is packaged by filling the groove with structural adhesive. In order to avoid that the outer water-pressure is applied on the epoxy resin through the structural adhesive, a gap between the two types of glues is left. The relationships between the stress of the riser and the tension, pressure, temperature of the single sensor are discussed, respectively. The measured tension sensitivity is 136.75 pm/KN while the minimum R-square value is 0.99997. The experimental results also show that there is a good linear response between water-pressure and the Bragg wavelength from 0 to 30MPa, and the sensor can even survive under the pressure more than 30MPa. In addition, the Bragg wavelength shifts linearly with the increasing temperature from 0 to 40°C. So, the pressure and temperature can be easily compensated if another sensor without tension is used.

The excitation of surface field and evanescent enhancement in the graphene based optical waveguide have shown sensitive to the refractive index of surrounding media and potential applications in high-sensitivity biochemical sensing. In this paper, we investigate the graphene-coated microfiber Bragg gratings (GMFBGs) with different diameters for ammonia gas sensing. The maximum sensitivity with 6 pm/ppm is achieved experimentally when the microfiber’s diameter is ~10 μm. Moreover, by adjusting the diameter of the GMFBG, the sensing performance of the GMFBGs can be optimized. Experimental results indicate, when the diameter is range of 8~12 μm, the GMFBG shows the characteristics of high sensitivity, relative low attenuation, and large dynamic range.

We demonstrate the fiber Bragg grating (FBG) vibration sensors working at a frequency up to 900 kHz. The FBGs were surface-mounted on the piezoelectric (PZT) ceramic, which is used as the vibration sensor head. A nonlinear response was measured with a periodically strong response at the frequencies of 1 kHz, 5 kHz, 12 kHz, 40 kHz, 70 kHz and 400 kHz. Four kind of polymer were used to package the FBG on the PZT plate. The gratings have similar pattern of vibration response with different deviation on the output voltage. The FBGs packaged with the polymer 705B and EPO-TEK 353ND were found to have a better response at lower frequency, while the FBGs packaged with the polymer T120-023-C2 and TRA-BOND F112 have a better response at higher frequency. The sensors could be developed for the real-time monitoring of the large infrastructure.

In this article we propose a novel Raman spectroscopic sensor which employs silicon nanowire waveguides for excitation and collection of Raman signal, and an integrated micro-ring resonator as a filter. Preliminary experimental results show that the extinction ratio of the filter including the ring resonator together with the grating coupler is more than 60 dB and the total insertion loss from the laser to the detector is less than 10dB. Theoretical calculations indicate that this high stray light rejection of the filter allows the observation of Raman signal at frequency as low as 4 cm^-1 . By employing the evanescent field of the silicon waveguide as excitation and collection of Raman signal, along with the integration of the filter and potentially a tunable semiconductor laser and the detector, a miniaturized Raman spectroscopic sensor can be realized on SOI platform

Optical fiber is made of glass, an insulator, and thus it is immune to strong electromagnetic interference. Therefore, fiber optics is a technology ideally suitable for sensing of partial discharge (PD) both in transformers and generators. Extensive efforts have been used to develop a cost effective solution for detecting partial discharge, which generates acoustic emission, with signals ranging from 30 kHz to 200 kHz. The requirement is similar to fiber optics Hydro Phone, but at higher frequencies. There are several keys to success: there must be at least 60 dB signal-to-noise ratio (SNR) performance, which will ensure not only PD detection but later on provide diagnostics and also the ability to locate the origin of the events. Defects that are stationary would gradually degrade the insulation and result in total breakdown. Transformers currently need urgent attention: most of them are oil filled and are at least 30 to 50 years old, close to the end of life. In this context, an issue to be addressed is the safety of the personnel working close to the assets and collateral damage that could be caused by a tank explosion (with fire spilling over the whole facility). This paper will describe the latest achievement in fiber optics PD sensor technology: the use of phase shifted-fiber gratings with a very high speed interrogation method that uses the Pound-Drever-Hall technique. More importantly, this is based on a technology that could be automated, easy to install, and, eventually, available at affordable prices.

In this paper, a novel method for an ultrahigh resolution optical spectrometry based on Brillouin dynamic gratings (BDGs) is proposed and demonstrated. A coherent acoustic wave is generated in an optical fiber through stimulated Brillouin scattering, and the acoustic wave modulated the fiber refractive index forming a BDG. An ultra-narrow bandwidth optical filter is constructed by operating a BDG in a long single-mode fiber (SMF), and the optical spectrometry is performed by sweeping the center wavelength of the BDG-based filter through a swept-tuned laser. In the experiment, a 4-fm (0.5 MHz) spectral resolution is achieved by operating a BDG in a 400-m SMF.

Microbubble resonators combine the unique properties of whispering gallery mode resonators with the capability of integrated microfluidics. The microbubble resonator is fabricated by heating the tapered tip of a pressurized glass capillary with oxyhydrogen flame. Firstly, a microtube with a diameter of 250um is stretched under heating of oxyhydrogen flame, the heating zone length is set to be 20mm and the length of stretch is set to be 7000um.Then nitrogen will be pumped in to the tapered microtube with the pressure of 0.1Mpa, the tapered tip will be heated by the oxyhydrogen flame continuously until a microbubble forms. An optical fiber taper with a diameter of 2 um, fabricated by stretching a single-mode optical fiber under flame was brought in contact with the microbubble to couple the light from a 1550nm tunable diode laser into the whispering gallery mode. The microbubble resonator has a Q factors up to 1.5 × 10⁷ around 1550nm. Different concentrations of ethanol solution (from 5% to 30%) are filled into it in order to test the refractive index sensing capabilities of such resonator, which shows a sensitivity of 82nm/RIU.

The magnitude of light intensity on the photo-to-electric detector fluctuates all the time in an optic fiber sensing system, because of the influence of various factors in the fiber optic sensing system and from the external environment. As a result of the excessive intensity, the electric signal will be overload after the amplifier circuit with constant enlargement factor, and when the light intensity becames too small, it will reduce the signal-to-noise ratio of the electric signal. Therefore, it is necessary to introduce an automatic gain control (AGC) module into the system, which can insure the electric signal in a reasonable magnitude. In order to solve the problem of optic intensity fluctuating in the optical fiber sensing system with PGC modulation and demodulation, in this paper, firstly, it is analyzed that the impact of different magnitudes of interferential intensity to the PGC demodulation in theory. Secondly, a reasonable control method is put forward and an AGC module based on the AD602 chip is designed and produced. Finally, it is proved that the optic fiber sensor system with an AGC module has strong ability to resist fluctuation of light intensity within 40dB.

Two kinds of tunable Thulium-doped fiber laser (TDFL) respectively using a Sagnac loop mirror and a novel tunable multimode interference (MMI) fiber filter are experimentally demonstrated. The TDFL with the Sagnac loop mirror made by a 145.5-cm polarization-maintaining fiber (PMF) can operate with stable dual-wavelength lasing or tunable single-wavelength lasing around 1860nm. Both stable dual-wavelength and tunable single-wavelength lasing are achieved by adjusting a polarization controller in the Sagnac loop mirror. The TDFL with a novel tunable MMI fiber filter formed by splicing a segment of a special no-core fiber that is an all silica fiber without fiber core to single mode fibers can achieve tuning range from 1813.52 nm to 1858.70 nm. The no-core fiber with a large diameter of 200 μm is gradually vertically covered by refractive index matching liquid, which leads to a wavelength tuning of the transmission peak of the MMI fiber filter. The relationship between the refractive index of the refractive index matching liquid and the peak wavelength shift of the MMI fiber filter is also discussed. Using the MMI fiber filter, a Thulium-doped fiber laser with a tuning range of 45.18 nm is demonstrated.

Wavelength division multiplex technology can enhance the sensing capacity by detecting various samples simultaneously. Whisper-Gallery-Mode (WGM) can be selected simulated in the micro-bubble by a directional coupler made by Si3N4 grating. Some grating parameters, including period, width, and refractive index modulation are numerically simulated by FDTD solution software to find their impacts on the WGM selected process. Grating with a particular period can simulated a WGM in micro-resonator on purpose. The interference of different bubble resonators is also discussed in this paper.

High-intensity focused ultrasounds (HIFUs), as a novel non-invasive surgery technology, have been used effectively for cancer therapy. In order to ensure the HIFU treatment safety, the acoustic pressure distributions and the size of the focal regions of HIFU fields need to be measured accurately. In this paper, the lateral sensitive and tip-sensitive all-silica fiberoptic Fabry–Perot ultrasonic hydrophone systems and the corresponding experimental setups are established to measure HIFU fields, respectively. The acoustic pressure distributions of the HIFU field along the X-axis, Y-axis, and Z-axis are compared in the degassed water by the lateral sensitive and tip-sensitive fiber-optic Fabry-Perot ultrasonic hydrophones. Experimental results show that the tip-sensitive configuration can measure the acoustic pressure distribution in the focal region with high accuracy than the lateral-sensitive configuration.

Clad-modified with nanocrystalline metal oxide fiber optic gas sensors have been proposed for ambient temperature operation. The sensor output light intensity either increases or decreases when the gas concentration is increased. Study shows that optical properties of metal-oxides with air medium influence the gas sensing. Absorption characteristics of nanocrystalline metal oxides ( ZnO, Sm₂O₃ and Ce doped ZnO etc., ) in air, methanol, ethanol and ammonia are analyzed as well as their effect on gas sensing.

Accurately measuring the acoustic pressure distributions and the size of the focal regions of high-intensity focused ultrasound (HIFU) fields, as well as the temperature induced by the HIFUs, are significant for ensuring the efficiency and safety of treatments. In our previous work, a tip-sensitive all-silica fiber-optic Fabry–Perot (TAFOFP) ultrasonic hydrophone for measuring HIFU fields is developed. In this paper, we explore the possibility that utilizing the TAFOFP ultrasonic hydrophone to simultaneously measure the acoustic pressure of HIFU fields and the induced temperature. The TAFOFP ultrasonic hydrophone for simultaneously measuring the acoustic pressure and temperature is developed and the experiment setup for measuring the HIFU fields based on the developed TAFOFP ultrasonic hydrophone is established. The developed TAFOFP ultrasonic hydrophone is experimentally tested in the degassed water and tissue phantom to verify the possibility of simultaneously measuring the acoustic pressure and temperature. Experimental results show that the sensing system can simultaneously measure the acoustic pressure and temperature.

A novel positioning algorithm based on super-resolution time delay estimation in dual Mach-Zehnder interferometry disturbance sensor is employed. We first compute the twice correlation function of the two output signal of DMZI by using modified chirp z-transform. Then fine interpolation of correlation peak is adopted to compute waveform of the main correlation peak only using the main segment of the cross power spectrum to improve the resolution of the twice correlation function. At last, in order to enhance the capacity of peak detection, we calculate the difference between the correlation function and its Hilbert transform to sharpen the peak of the correlation function. We have experimentally demonstrated that the proposed positioning algorithm can improve the positioning resolution and accuracy, and it has the potential to accurate positioning in low sampling rate and reduce costs of the system.

Pressure method using polarization-maintaining photonic crystal fiber (PM-PCF) as sensing element based on Sagnac interferometer is proposed to monitor inter layer pressure in especial compact structure. Sensing model is analyzed and test system is set up, which is validated by experiment. The birefringence can be modified by the deformation of PM-PCF under transverse pressure, realizing pressure measurement by detecting the wavelength shift of one specific valley from output of the Sagnac interferometer. The experiment results show that the output interference fringes were shifted linearly with pressure. The dynamic range of 0 kN ~10kN, sensing precision of 2.6%, and pressure sensitivity of 0.4414nm/kN are achieved, and the strain relaxation phenomenon of cushion can be observed obviously. The sensor has better engineering practicability and capability to restrain interference brought up by fluctuation of environment temperature, which temperature sensitivity is -11.8pm/°C.

Optical fiber ground wire (OPGW) is used for both the earth line and communication line in electric power systems. It is important to find an effective to monitor the status of OPGW and diagnose some possible damages. Fault location of the optical fiber transmission line, lightning stroke location and early-warning of ice covering of OPGW are common tasks for OPGW health monitoring and maintenance. As to these issues, Brillouin optical time domain reflectometry (BOTDR) is employed for the health monitoring of OPGW. In experiment, a positive electrode with high pulsed current and a negative electrode are adopted to form a lightning impulse system with duration time of 200ms for simulation of the lightning stroke process, and a tensile force loading apparatus is also constructed to simulate the strain influence of the ice covering on the OPGW. Experimental results demonstrate that the BOTDR can sensitively locate the lightning stroke incidents with the quantity of electric discharging larger than 100C and the strain component has little interference on temperature monitoring as the fiber contained in the OPGW is generally free of strain, and in the ice covering condition the strain feature appears only when the extra tensile force on the OPGW is over 30kN. In addition, the vibration of OPGW does not disturb both the temperature and strain monitoring. As to further applications of distributed optical fiber sensors (DOFS) for the OPGW health monitoring, it is important to enhance its spatial resolution.

We propose a novel strain sensing based on fiber-optic Mach-Zehnder Interferometer. A vortex beam is generated by a vortex fiber in the reference arm, and interferes with the fundamental Gaussian beam in the sensing arm to generate an interference spiral pattern. A camera is used to record the sequential frame of the spirals, and digital image processing technique is employed to recognize the rotation angle of the spirals induced by the strain under measurement. By this method, a strain resolution over 10^-9 can be reached easily with a small measurement deviation. Besides, we compare the sensing characteristics for the cases of the optical vortex carrying different topological charges, and prove that the optical vortex with charge one fits our sensing application best.

Based on the principle of surface plasmon resonance (SPR) sensor, the influence of mental film was illuminated. According to the MATLAB simulation, the performance of SPR sensor using Au and Ag film was compared. The optimal thickness was 52nm and 38nm, respectively. In view of the features of Au and Ag film, Ag+Au hybrid metal film was proposed. On the basis of simulated result, it could be concluded that the performance of SPR sensor with 50nm composite film (Ag film 20nm ) was excellent.

Laser airborne particle counting sensor (LAPCS), based on light scattering of particle, is specially used in clean environment monitoring. LAPCS samples the air by a pump, and uses a laser illuminating the sampled air in the chamber, then counts the total number of scattering signal and its amplitude distribution, which can characterize the number of particles and size distribution. The structure of air-flow-path in LAPCS directly influences the flow of sampling air, the particle trajectories and velocity distribution in chamber that will influence the performance of LAPCS. In this paper, a finite element arithmetic based on Ansys Fluent14 software environment was developed to simulate the air flow and particle flow in LAPCS. Based on numerical calculations, velocity distribution of airflow and particle trajectories in chamber of LAPCS with different nozzles are presented intuitively. A few particles probably are disturbed outside the air-flow path and pass the photosensitive area many times, which can make the LAPCS iteration count. The results can provide a theoretical basis for optimizing design of the LAPCS.

A Fabry-Perot interferometer sensor based on a fiber-tip bubble-structure micro-cavity is proposed, fabricated, and demonstrated for hydrostatic pressure sensing and transverse load sensing. A segment of a well-cleaved multimode fiber with a core diameter of 62.5μm is processed with chemical etching based on a solution of HF 40% and the bubblestructure micro-cavity is fabricated by using arc discharge at the end of the processed multimode fiber. The sensor can be considered as a two-beam Fabry-Perot interferometer with one beam from the silica-air interface on the left side of the bubble and the other from the air-silica interface on the right side of the bubble. The broadband light is injected into the fiber-tip bubble-structure micro-cavity by splicing the multimode fiber with the bubble-structure micro-cavity to a 3- dB optical coupler and the reflective spectrum of the bubble-structure micro-cavity is measured by an optical spectrum analyzer. Both hydrostatic pressure sensing with a sensitivity of ~0.1 nm/MPa and transverse load sensing with sensitivity of 3.64 nm/N are experimentally demonstrated based the proposed fiber-tip bubble-structure micro-cavity sensor. The proposed sensor is demonstrated with a relative low temperature sensitivity of about 2 pm/°C. Properties of the fiber-tip bubble-structure micro-cavitys with different sizes are investigated. The sensor has the advantages of lowcost, ease of fabrication and compact size, which make it a promising candidate for hydrostatic pressure sensing or transverse load sensing in harsh environments.

We propose and demonstrate a highly sensitive optical fiber microfluidic refractometer. A microhole is fabricated in the photonic crystal fiber (PCF) by using femtosecond laser beam, which combines the tunable mode coupler and microfluidic channel. The mode field diameter of the guided light is changed with the refractive index in the microfluidic channel, which results in the tunable coupling ratio between the core and the cladding in the PCF. Therefore, the refractive index of the liquid in the microfluidic channel is detected by interrogating the fringe visibility of the reflection spectrum. These experiments results demonstrate that the sensor is insensitive with the temperature and strain, and a RI sensitivity of up to 150.7 dB∕RIU is achieved, establishing the tunable mode coupler as a sensitive and versatile sensor.

Passive ring cavities are now treated as the most promising sensitive elements for cheap and technologically simple microoptical gyro for mass production. Usually the single-mode planar waveguides are considered to be the only possible technology for such devices implementation. However, our analysis shows that in some cases the confocal ring cavity, characterized by degeneration of transverse modes, can be the better alternative for such a device technology. The paper considers possible advantages and disadvantages of such an approach, its limitations and technology prospects.

A fiber optic Fabry-Perot accelerometer (FOFPA) with diaphragm-mass-collimator (DMC) gathered structure is presented. This design makes the structure more compacts and the manufacturing process more controllable. The operation principle based on Fabry-Perot interference is described. Several tests using intensity demodulation scheme which can control the working point of FOFPA were carried out. Experimental results show that: axis sensitivity of the proposed FOFPA is 36.07 dB (re: 0 dB=1 V/g) with a fluctuation less than 0.9 dB in a frequency bandwidth of 10-125 Hz, the resonant frequency is about 350 Hz, measurement range is about 70 dB@100 Hz. which are much close to theoretical values

The paper proposes an accelerometer construction based on 45-degrees Fabry-Perot (F-P) interferometer cavity. The uniform intensity cantilever consists of a mass block in the middle and a 45-degrees F-P cavity fixed inside the mass. The mass block can oscillate freely when the vibrating sensor is subject to the vibration and the F-P cavity length is changing. The G-lens end face and total reflective film make up the two reflective films of the F-P cavity, and the reflectivity are 4% and 90% respectively. In the F-P cavity, a 45-degrees mirror fixed in the middle of the G-lens and total reflective film. The mirror can change the transmission of the light and increase the optical path difference. The total reflective film fixed in the steel tube and the G-lens fixed in the fine tuning bolt. The bolt can fine adjust the F-P cavity in sensor encapsulating. The sensor structure lead to the optical loss in the airborne and tilted mirror, besides the distance of F-P gap in steel tube and the optical coupling efficiency can’t work out accurately, so we did a series deterministic test before encapsulating, for example the selection of the structures, the diameter of the optical fibers and the diameter of the reflective films. At last, 9/125 μm optical fiber, 1.4 mm total reflective film and the structure of total reflective film out of steel tube were used for the accelerometer. The sensitivity can reach 0.042 rad/g and the resonant frequency of the accelerometer is 400 Hz.

Porous silicon material and device has attracted more attention for use as biochemical optical sensors. In this paper, A novel porous silicon-based multilayer dielectric-grating structures by adding high-reflectivity porous silicon stacks between the substrate and grating was fabricated, and the porous silicon grating height was set to be about 200 nm, the grating period was 4 μm, the air filling factor was 50%. A new better method of preparing this porous silicon-based multilayer dielectric-grating structures have also been employed.

A novel evanescent field refractometer based on a two-core photonic crystal fiber (TWPCF) sandwiched between multimode fibers(MMFs) is demonstrated. Through splicing a short piece of TWPCF between two MMFs, a simple structure and high sensitivity RI sensor can be constructed. Instead of using wavelength information as sensor signal, we focus more on the light intensity signal different from most PCF based RI sensor. The TWPCF section functions as a tailorable bridge between the excited high order modes and the surrounding refractive index (SRI). With a light filter inserting in the front of white light, the transmission spectrum of the light through the sensing region occurs in a welldefined wavelength bands. As a result, the peak power of the transmission light is tailored with the SRI perturbation via the MMF-TWPCF–MMF structure. The experiment result shows a quadratic relation between the light intensity and samples within RI range of 1.33-1.41 while a linear response can be achieved from the 1.33-1.35 which is a most used RI range for biologically sensing.

We report a type of multimode fiber interferometers (MMI) formed in photonic crystal fiber (PCF). To excite the cladding modes from the fundamental core mode of a PCF, a coupling point is formed. To form the coupling point, we used the method that is blowing compressed gas into the air-holes and discharging at one point, and the air-holes in this point will expand due to gas expansion in the discharge process. By placing two coupling points in series, a very simple all-fiber MMI can be implemented. The detailed fabrication process is that the one end of the PCF is tightly sealed by a short section of single mode fiber (SMF) spliced to the PCF. The other end of the PCF is sealed into a gas chamber and the opened air holes are pressurized. The PCF is then heated locally by the fusion splicer and the holes with higher gas pressure will expand locally where two bubbles formed. We tested the RI responses of fabricated sensors at room temperature by immersing the sensor into solutions with different NaCl concentration. Experimental results show that as refractive-index (RI) increases, the resonance wavelength of the MMI moves toward longer wavelengths. The sensitivity coefficients are estimated by the linear fitting line, which is 46nm/RIU, 154mn/RIU with the interferometer lengths (IL) of 3mm and 6mm. The interferometer with larger IL has higher RI sensitivity. The temperature cross-sensitivity of the sensor is also tested. The temperature sensitivity can be as low as -16.0pm/°C.

We reported two kinds of fiber sensor based on double cascaded single mode fiber corners, which has a high sensitivity for refractive index (RI) sensing. RI sensing was experimentally demonstrated with average sensitivity of 95.5nm/RI unit (RIU) in a RI range from 1.333 to 1.421 and the other is 235nm/RI unit (RIU) from 1.333 to 1.418, which are relatively high among the previously reported similar fiber sensors (e.g., it is about 10 times higher than that of the normal two or three-cascaded-taper based Mach–Zehnder interferometer). Besides, The proposed RI sensors were fabricated only by a fiber fusion splicer. So , the fiber sensor is quite easy to made.

We present a wavelength-tunable tapered optics fiber surface Plasmon resonance (SPR) sensor by polishing the end faces of multimode fibers(MMF).Two hard plastic clad optical fibers joint closely and are used as the light input and output channels. Their end faces are polished to produce two oblique planes, which are coated with gold film to be the sensing surface and the front mirror. The presence of the tapered geometry formed by the two oblique planes in the orthogonal directions makes it possible to adjust incident angle through changing the tilt angles of the two end faces, so as to achieve tuning the SPR coupling wavelength-angle pair. Compared with previous researches based a tapered optic fiber probe, we report the approach theoretically increase the signal noise ratio (SNR) by separating incident and emergent light propagating in the different coordinate fiber. Since fabricating the sensing surface and the front mirror on the two fibers to replace one single fiber tip, there is more incident light can reach the sensing surface and satisfy SPR effective. In addition, this improvement in structure has advantages of large grinding and sensing area, which can lead to high sensitivity and simple manufacture process of the sensor. Experimental measurement demonstrates the sensor has a favorable SPR resonanceabsorption and the ability of measuring refractive index (RI) of aqueous solution. This novel tapered SPR sensor has the potential to be applied to the biological sensing field.

Femtosecond laser is used to inscribe the reflectivity-changed mirrors in the single mode fiber that formed the device named cascaded Fabry-Perot micro-cavities, with details of fabrication given. The cascaded Fabry-Perot micro-cavities are made up of three reflected mirrors with different lengths of microcavities. By establishing the theoretical model of the device with the transfer matrix method, the effect of the cascaded Fabry-Perot micro-cavities can be seen as a superposition of the two Fabry-Perot cavities. Its reflection fringe contrast is experimentally up to 10dB. The proposed structure is regarded as an effective way to strengthen the contrast in order to improve the sensing resolution.

The bending characteristics of the long period fiber grating (LPFG) in hollow eccentric optical fiber (HEOF) were investigated experimentally. The results indicate that the HEOF-LPFG is insensitive to the bending and the biggest sensitivity only is 1.3nm/m^-1 in the range of 0~5m^-1. More than that, the dependences of the resonant peak on the temperature and the axial strain were also studied, obtaining the response of 56.7 pm/°С and 0.3 pm/με, respectively. Obviously, the HEOF-LPFG is more sensitive to the temperature and immune to the curvature and the strain. The HEOF-LPFG can be employed to measure the single parameter and simplify the measurement equipment in the practical application.

A simple structure of all-solid microstructured fiber, which is composed of 8 linear arrays of high refractive index dielectric rods radially symmetry arranged around a low refractive index substrate, is proposed and numerically investigated. The calculated results show that the space between the adjacent band gaps is very small, minimum loss of 0.35 dB/km can be achieved. With increasing the distance between high refractive index rods and the refractive index difference between the high refractive index rod and the core, the band gap will move to the long wavelength. With decreasing the bending radius, the short wavelength edge of PBG is significantly affected and shifts to the long wavelength, while long wavelength edge of PBG suffers relatively little impact. By adjusting the layer number of high refractive index dielectric rods, we can effectively change the effective mode area, resulting in large mode area fiber.

Remote laser spectroscopy availability for airborne search of radionuclides polution has been examined. Experiments were carried out under the CARS circuit. The method of remote detection a radionuclide in atmosphere from container burial places and in places of recycling the fuel waste of the atomic power station is elaborated. Preliminary results of investigation show the real possibility to register of leakage of a radionuclide with concentration at level of 10¹²÷10¹³ см^-3 on a safe distance from the infected object.

We have developed airborn lidar system to detect pipeline leakage and explore oil and gas deposits. Test flights indicate that a sensitivity of 6 ppm for methane and 3 ppm for hydrogen sulfide has been reached for leakage detection. As estimations have shown the reliability of HHG detection can exceed 80% at the integration method of seismic prospecting and laser remote sensing.

Recently, we found that by terminating a long length of fiber of up to 1 km with an in-fiber cavity structure, the entire structure can detect vibrations over a frequency range from 5 Hz to 100 Hz. We want to determine whether the structure (including packaging) can be optimized to detect vibrations at even higher frequencies. The structure can be used as a distributed vibration sensor mounted on large motors and other rotating machines to capture the entire frequency spectrum of the associated vibration signals, and therefore, replace the many accelerometers, which add to the maintenance cost. Similarly, it will help detect in-slot vibrations which cause intermittent contact leading to sparking under high voltages inside air-cooled generators. However, that will require the sensor to detect frequencies associated with vibration sparking, ranging from 6 kHz to 15 kHz. Then, at even higher frequencies, the structure can be useful to detect acoustic vibrations (30 kHz to 150 kHz) associated with partial discharge (PD) in generators and transformers. Detecting lower frequencies in the range 2 Hz to 200 Hz makes the sensor suitable for seismic studies and falls well into the vibrations associated with rotating machines. Another application of interest is corrosion detection in large reenforced concrete structures by inserting the sensor along a long hole drilled around structures showing signs of corrosion. The frequency response for the proposed long-gauge vibration sensor depends on packaging.

The performance of the fiber optic current sensors (FOCSs) is limited by the linear birefringence (LB). Faraday mirror can be employed to compensate the LB by exploiting the non-reciprocity of Faraday effect and the reciprocity of LB. In this paper, the structure and principle of the FOCS using Faraday mirror are addressed, and the simulated results showing the influence of LB on FOCS are presented. The results indicate that the influence of LB disappears when the current is null. However, when the current is not zero, the LB is not removed and the extent of effect is different with different LB. Considering the LB is not easy to remove, a method to directly measure Faraday rotation in the presence of LB by time multiplexing of three different states of polarization is proposed. The Faraday rotation can be deduced directly from the detected signals and the LB need not be compensated physically by employing this technique.

The idea of using the method of spatial filtering velocimetry based on a linear CMOS image sensor is proposed to provide accurate velocity information for vehicle self-contained navigation system. A new method is proposed to determine the error source of the system. The image sensor is employed both as a detector and as a pair of differential spatial filters so that the system is simplified. The spatial filtering operation is fully performed in a field programmable gate array (FPGA). The approach of fast Fourier transform (FFT) is employed to obtain the power spectra of the filtered signals. Because of limited frequency resolution of FFT, a frequency spectrum correction algorithm, called energy centrobaric correction, is used to improve the frequency resolution. The velocities of the side surface of a high precision rotary table and the radiating frequencies of an LED are measured. The experimental results show that the measuring error of velocity of a rotary table is about 0.73% and the measurement uncertainty of 1000 times tests is 0.55%; the radiating frequency of an LED is measured under the condition of no imaging system, and the measurement uncertainty turns out to be within 10^-5. Error sources of the system are analyzed and it is concluded that the main error source of the device is the imaging system. In a word, the velocimeter can satisfy the requirements of non-contact, real-time, high precision and high stability velocity measurement of moving surfaces and has the potential of application to vehicle self-contained navigation system.

A fiber-optic temperature sensor based on specialty triple-clad fiber (STCF) is proposed. Based on coupling mode theory, the STCF can be equivalent to a rod waveguide and two tube waveguides. The different mode dispersion curves are calculated and a resonance wavelength is obtained. A straightforward experiment is performed to prove the temperature sensitivity. Experimental results shows that the temperature sensitivity can be achieve 97.2pm /°C in 20~90°C and there is a good repeatability. The resonance wavelength has a red shift and increase as increasing temperature. Thus, this sensor can be used for temperature monitoring in time.

The drift of birefringence difference can be caused by the ambient temperature variety of the fiber, which will lead to the change of lightwave polarization mode in the fiber. In the resonator fiber optic gyro systems, the change of lightwave polarization mode of the light transmission in the fiber can bring about the measurement error of the system. The hollowcore photonic crystal fiber (HCPCF) resonator is designed to reduce the drift of birefringence difference caused by the temperature variety. It is verified experimentally that the temperature coefficient of the HCPCF birefringence difference is decreased about two orders of magnitude which is lower than that of the normal polarization maintaining fiber (PMF).

Fiber optic sensor (FOS) has received much attention in the field of Structure Health Monitoring (SHM) due to its advantages of low weight, small size, high sensitivity multiplexing ability, free of electromagnetic interference and long durability. However, in harsh environments, structures often undergo large strain where few traditional fiber optic sensors could survive. This paper report a novel material with features of light-transparent, chemically inert, thermally stable material Polydimethylsiloxane(PDMS) fabricated large axial/shearing strain sensor. The sensor was fabricated by directly coupling a conventional signal mode fiber into half cured PDMS material using a translation stage under the inspection of a microscope. Meanwhile, a laser diode and a photo detector were used in the fabrication process to make sure the sensor achieved minimum light loss. An experiment was conducted later to investigate the sensor’s transmission characteristic in 1310nm infrared laser relating with the applied axial/shearing strain. The results show that the proposed sensor survived an axial strain of 6 7.79 x 10⁶ με ; a shear of 4 6.49 x 10⁴ με with good linearity and repetition. The experiment indicates that the proposed sensor can potentially be used as strain sensing elements in Structure Health Monitoring systems under earthquake or explosion.

In recent years, there has been a rapid rise in the use of pulse cavity ring-down spectroscopy to determine the optical properties of atmospheric aerosols. In the present work ,we describes the design and performance of a CRDS system for measuring extinction coefficients of atmospheric aerosols. CRDS based methods can achieve impressive sensitivity owing to the long effective path lengths involved. More importantly, the method is not affected by laser intensity fluctuations since the rate of attenuation of light is the measured variable rather than absolute irradiance. The extinction coefficient is a function of the cavity ring-down time. Determining an accurate decay time is critical to precise measurements of the extinction coefficients. The average and standard deviation of the decay time (τ₀ is measured 6 hours ,cavity filled only with dry nitrogen) is about 42.21μs and 0.16μs, respectively. Moreover, a minimum detectable aerosol extinction coefficient of 0.41Mm^-1 is achieved. Allan deviation plots for the value of τ₀ measurements, close to a flicker noise. The minima(~5.8x10^-4μs) in the Allan plots indicate the optimum average time(~60s) for optimum detection performance. To test the performance of the CRDS system, we monitored the optical properties of ambient aerosols on the campus of the Zhejiang Normal University from January 3rd to January 7th, 2014. During this period, the average value of the extinction coefficient is 816.8Mm^-1, a maximum value more than 1800 Mm^-1, and a minimum aerosol extinction coefficient of 119.27 Mm^-1 is detected.

We have carried out a detailed simulative study of the photonic band-gap crystal fiber sensor sensitivity by using the finite difference beam propagate method. The effect of the incident wavelength and the fill factor on the relative sensitivity of the sensors has been simulated. The simulative results show that with the incident wavelength and the fill factor increased, the relative sensitivity will be improved, the sensitivity of photonic band-gap crystal fiber sensor will be higher. The simulation results can provide the guidance for the further experimental study.

The aperture-field mapping is very important to diagnosing the amplitude and phase distribution of the antenna under test( AUT). Since such measurements need to be done without influence to the actual field distribution near the aperture, traditional metallic near-field probes, such as horn antennas, waveguide slots, et al, are irrespective. Miniature electrooptic E-field sensors offer good possibility for such near-field or very near-field measurements, because of its small size and little perturbation to the AUT. Moreover these devices have high resolution and reduced dimensions. In this paper, we have present a simple photonic microwave probe to measure the electric field vector distribution at a distance shorter than one wavelength from the aperture plane of a antenna. The photonic E-field probe is a type of pigtailed electro-optic sensor and consists of an electro-optic crystal supported by a quartz sleeve. The probe is all-dielectric, without any metallic materials. Those physical and electrical features make the photonic sensor attractive when used as a probe for near-field antenna measurements. A patch antenna with a resonant frequency at 6.5GHz was designed and fabricated. Both amplitude and phase distribution of the two tangential E-field components are mapped by using the present photonic probe. Simulation was carried out as well, and compared with the experimental measurements. The result shows great correspondence for amplitude distribution between simulations and experiments, as well as for the phase distribution except for some random tiny fluctuations. The methods to improve the stability of measurement system are briefly discussed.

So-called spectral ripple a special phenomenon only existing in fold-type cavity ring-down spectrometer, and it is believed as deriving from the interference effect of different lights on the folded mirror. To investigate the influence of this phenomenon, on fold-type cavity ring-down measurement, some representative instances of laser linewidth are simulated and analyzed, and some experiments are carried on. It is found that the increasing of laser linewidth can make the amplitude of the spectral ripple decrease, more importantly, which can make the ring-down signal no longer decay as a single exponential but as the double exponential function.

We present an optical fiber voltage sensor by Michelsion interferometer (MI) employing a Fabry-Perot (F-P) interferometer and the DC phase tracking (DCPT) signal processing method. By mounting a MI fabricated by an optical fiber coupler on a piezoelectric (PZT) transducer bar, a dynamic strain would be generated to change the optical path difference (OPD) of the interferometer when the measured voltage was applied on the PZT. Applying an F-P interferometer to demodulate the optical intensity variation output of the MI, the voltage can be obtained. The experiment results show that the relationship between the optical intensity variation and the voltage applied on the PZT is approximately linear. Furthermore, the phase generate carrier (PGC) algorithm was applied to demodulate the output of the sensor also.

We propose and demonstrate a trapped yeast cell being launched away from the fiber tip with a certain speed to a certain position without moving the optical fiber in a single fiber optical trapping system. We excite both LP01 mode and LP11 mode beams in a same normal communication fiber core to generate the optical scattering force and trapping force by molding the fiber tip into a special tapered-tip shape. A yeast cell of 6μm diameter is trapped and then being launched away. We construct the optical launching well by controlling the power of double mode beams. Besides that, we also built a physical model to analyze the micro particle dynamic behavior characteristics during the launching moment. This micro particle directional launching function expanded new features of fiber optical tweezers based on the normal communication fiber, providing for the possibility of more practical applications in the biomedical research fields.

With the progress of study on fiber optic gyroscope (FOG), the higher demand for performance of polarization maintaining fiber (PMF), and miniaturization is one of the important development direction. Compared to other stress-induced PMF, the birefringence of elliptical cladding type PMF has small effect when we make stress area smaller, and it can meet the requirements of fiber optic gyroscope. Therefore, 40 microns ultrafine diameter elliptical cladding type polarization maintaining fiber can be the preferred option of the FOG towards light, small, spiritual direction. In this paper, we use finite element method to analysis stress-induced birefringence of 40 microns ultrafine diameter elliptical cladding type PMF, get the stress contours on cross-section of PMF, and calculate the stress birefringence, the polarization mode field distribution and modal birefringence. Under the given simulation conditions, the magnitude of stress birefringence in core is about 10-4, and the magnitude of model birefringence is about 10-4. The results show that 40 microns ultrafine diameter elliptical cladding type PMF has a uniform stress field distribution and a large birefringence. It is conductive to achieve miniaturization of PMF.

A gas temperature and pressure measurement method based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) detecting linewidth of gas absorption line was proposed in this paper. Combined with Lambert-Beer Law and ideal gas law, the relationship between temperature, pressure and gas linewidth with Lorentzian line shape was investigated in theory. Taking carbon monoxide (CO) at 1567.32 nm for example, the linewidths of gas absorption line in different temperatures and pressures were obtained by simulation. The relationship between the linewidth of second harmonic and temperature, pressure with the coefficient 0.025 pm/K and 0.0645 pm/kPa respectively. According to the relationship of simulation results and detected linewidth, the undefined temperature and pressure of CO gas were measured. The gas temperature and pressure measurement based on linewidth detection, avoiding the influence of laser intensity, is an effective temperature and pressure measurement method. This method also has the ability to detect temperature and pressure of other gases with Lorentzian line shape.

High-precision 3-dimensional metallization is difficult to realize in specific nonmetallic areas by using the traditional methods such as wet-chemical and mechanical methods because of the disadvantage that usually they cannot achieve selective modification. In this paper, 3-dimensional laser scanning system was applied to achieve the modification of specific regions of the sample surface. In 3-dimensional laser scanning system, the laser beam, after going through dynamic focusing system, was reflected by galvanometers and then focused by f-theta lens on the sample surface. The changes in surface characteristics of the blends of polycarbonate and acrylonitrile butadiene styrene copolymers (PC/ABS) mixed with Cu-Cr complex by the laser irradiation with the wavelength of 1064nm were investigated. Through analysis it was found that the smooth surface of the original samples was changed to a micro-hole structure accompanied by an increased surface roughness as well as an increased water contact angle. The chemical composition percentage had changed and the metal components of copper and chromium were detected after the laser irradiation. The irradiated areas were degraded into organic ligand fragments, volatile gas and reducing metal ions of copper and chromium. Besides, the thickness of the deposited metal layer and the adhesive force between the metal layer and the substrate after electroless plating varied according to the laser parameters such as frequency and scanning speed. As shown in the experiment, the thickness of deposited copper layer exceeded 11μm and the deposited nickel layer exceeded 2μm respectively.