This PDF file contains the front matter associated with SPIE Proceedings Volume 8914 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The random noise of the fiber optic gyroscope(FOG) is not only concerned with the noise of the optical path in system, but also concerned with a various of noise in the modulation and demodulation circuit. The characteristics of the shot noise, thermal noise of the detector and the relative intensity noise of light source were analyzed. The random noise model was established by use of the closed-loop transfer function. The relationship between the fiber optic gyro random walk coefficient (RWC) and these noises was analyzed. According to the theoretical results, some parameters of the gyro were adjusted, and the performance of the gyro was optimized. The theoretical results were compared with the experimental data analyzed by Allan variance, the random walk coefficient model was proved correct.

Fiber Bragg gratings (FBGs) sensor has been widely used in all kinds of detection spaces. Nonlinear effects of the fiber Bragg gratings have been observed in high-temperature conditions, however, it occurred in low-temperature as well. In this paper, we take the low-temperature experiments in the low-temperature thermostat bath, temperature range from 10°C to -80°C, the Bragg wavelength shift with the temperature decreasing linearly at the very beginning and it shows linear characteristic range from room temperature to -45°C. However with the temperature goes down continuously, the nonlinear effects emerged, the turning point temperature of the nonlinear effect is at -45.3°C. Besides, the sensitivity of the FBGs decreased as well from 8.96pm/°C to 6.72pm/°C. Considering the physical characteristic of the silica fiber, which the thermo-optic coefficient and the thermal expansion coefficient of the fused silica is not constant if temperature goes down and it shows nonlinear features, therefore we conclude the nonlinear effect at low-temperature is attributed to the thermal expansion and the thermo-optic effect of the silica fiber. Thus, we predict that appropriate doping improvements in the silica fiber can modify the linear range of FBGs which can enhance the measure precision. In addition, we find that high sensitivity FBGs has a lower temperature turning point of the nonlinear effect. The invar packaged FBGs has a sensitivity of 24.3pm/°C at room temperature. It is higher than bare FBGs’ sensitivity which is about 8.96pm/°C at room temperature. The invar packaged FBGs’ temperature turning point is at about -54.5°C, which is lower than the bare FBGs’, -45.3°C, temperature turning point. This indicates that high sensitivity FBGs can also increase the linear temperature range. The experiment results and analysis show that we can either by increasing the sensitivity of FBGs or doping in the silica fiber to modify the linear range.

A quasi-distributed sensor system based on optical frequency domain reflectometry where the sensing points were identical, low-reflective fiber gratings in a single fiber was investigated. Firstly, the spatial distribution function of fiber gratings was deduced in theory, and the effects of interference among each sensing fiber grating and between the gratings with broadband reflector were investigated. Then the strain sensor system cascaded 215 fibers Bragg gratings (FBGs) in a single fiber had been numerical investigated, the spatial domain addressing and wavelength demodulation of the fiber gratings was implemented according to Fourier transform and inverse Fourier transform. Finally, the internal relations between interaction noise and distribution position of the gratings were simulation analysis. The results show that the interference exists among each sensing fiber grating，but it can be suppressed by buffer fiber. This allows obtaining more realistic values of the performance and design parameters such as the number of FBGs, the reflectivity of the gratings, and the distance between the sensors.

We report a temperature and pressure sensor based on fiber Bragg grating(FBG) lasers, the analytical expressions for the shift of the Bragg wavelength with temperature and pressure are derived, the effect of operation temperature of fiber Bragg grating on the central wavelength of fiber Bragg grating laser is discussed experimentally. The result demonstrates that the central wavelength of laser is a function of the operation temperature of FBG, and the temperature coefficient of the fiber Bragg grating is 1.27×10^-5/°C.

In this paper we report a fiber optical sensor system based on surface plasmon resonance (SPR) with real-time response for biochemical interaction analysis. The fiber sensor is constructed from a multi-mode fiber with plastic cladding. To facilitate the measurement, a software program is developed which integrates the data acquisition and processing for real-time feedback. Polynomial fitting is implemented to smooth out the noise in the transmission ratio and a spectral resolution of 0.2 nm is achieved. Ethyl alcohol and water mixtures with different concentrations are measured to demonstrate the system's real-time capability. This work is essential for the development of a compact, real-time fiber SPR biosensor.

Recently, many programs have been developed for simulation or analysis of the different parameters of light propagation in tapered optical fibers, either for sensing or for communication purposes. In this paper, it is shown the RSOFT BeamPROP as a fairly robust and simple program, due to the existence of a graphical environment, to perform simulations with good accuracy. Results are compared with other simulation analysis, focusing on multimode interference phenomena for refractive index sensing in a tapered optical fiber, where the wavelength of the incident light, in terms of waist diameter and tapered region length are optimized.

The center frequency of Brillouin scattering spectrum is easily influenced by the noise and the measurement accuracy of optical fiber strain is reduced. So a novel denoising method which can be applied in the Brillouin scattering spectrum is developed in this article. The Brillouin scattering spectrum is decomposed into multi-scale detail coefficients and approximation coefficients by using the wavelet transform. The wavelet decomposition detail coefficients are threshold quantified by utilizing the threshold algorithm. At the same time, the wavelet decomposition approximation coefficients are trained and simulated by using the BP neural network in order to remove noise hided in the approximation coefficients. So the novel method can reduce the wavelet decomposition scales. The Brillouin scattering spectrum which has a better denoising effect can be gained by using the inverse wavelet transform, and the measurement accuracy of optical fiber strain is enhanced also. The results of simulation and experiment demonstrate that the proposed method can suppress noise better; accordingly, the new method can gain more precision optical fiber strain and reduce the wavelet decomposition scales effectively than the conventional wavelet denoising method. Theory analysis and experiment show that the method is reasonable and efficient.

A fiber optic quasi-distributed sensing technique was suggested to use for detecting the location and severity of water leakage. A novel fiber optic sensor probe was devised with a vessel of water absorption material called as water combination soil (WCS) located between two highly reflected connectors. The largest vessel probe provides the highest sensitivity, 0.267 dB/ml, while the small one shows relatively low sensitivity, 0.067 dB/ml, and unstable response. The sensor probe with a high output value provides a high sensitivity with various detection levels while the number of total installable sensor probes decreases.

A novel filter with dual micro-ring in series is theoretically investigated basing on the coupled modes and transfer matrix method in this article. A combiner is added to connect the output of through port and drop port in contrast to conventional structure. Under an ideal condition, the transmission spectrum intensity is worked out by employing transfer matrix method and the final output spectrum is analyzed by the simulation of Matlab. In addition, the effects of the coupling coefficient and other parameters are discussed in detail. The simulation results show that when the coupling coefficient of two micro rings is equivalent to straight waveguide counterpart, the output spectrum appears pseudo-norm and a periodic output spectrum phenomenon any way; In contrast, when the coupling coefficient of dual micro-ring and straight waveguide are different, we can find the free spectral range becomes 3 ,4 times higher than the single micro-ring model structure as dual micro-ring radius is 297.6μm, 396.8μm, respectively. Furthermore, the pseudo-norm is small enough to be neglected. Then, the perfect extinction ratio and the extraordinary narrow bandwidth with quality factor of 10⁵ are maintained. In comparison of conventional dual micro-ring filter, the pseudo-norm in this article is much better restrained and the property of micro-ring resonator achieves a distinct-obvious progress as a result. The proposed filter greatly enhances the free spectral range and has broad prospect of application.

The Brillouin scattering light signal is a wideband signal containing a lot of phase noises and amplitude noises. And the envelope of the Brillouin scattering signal will include some characteristics due to the influences of temperature and strain change on the sensing fiber. In order to obtain the useful temperature and strain change information, the amplitude demodulation of the noise signal should be conducted, and at the same time, it is necessary to effectively suppress the signal noise. In this paper, Morlet wavelet has been used to do the envelope detection since it has band-pass filtering function and signal demodulation function provided by the orthogonal characteristic between real part and imaginary part. Moreover, the Morlet wavelet function has the characteristic of time-frequency analysis, and it can analyze envelope of the signal and extract characteristic of the signal in the whole frequency range by changing the scale factor and translation factor. Meanwhile, it can also suppress the signal noise effectively. The simulation model has been built to verify the validity of envelope demodulation principle by Morlet wavelet algorithm. Theory analysis and experiment show the algorithm is reasonable and efficient.

In recent years, Fiber Bragg Grating (FBG) sensors have been attracted a lot of interest, and widely and increasingly researched in many important areas. In this work, we present the field of railway dynamic monitor concerning the application of FBG sensors. We have built the principle and established the sensing system based on FBG to monitor the situation of train and railway through the analysis of track strain during the train passage. We have illustrated that FBG sensors set on the lateral and underside of the rail can detect the strain of rail and sensors on different positions show distinct results. We have presented that the underside of the rail structure is the most suitable position to monitor the strain in railway.

An integrated fiber-optic turbulence sensor based on non-balanced fiber-optic Mach-Zehnder interferometer with a small air gap as light path difference has been designed for detecting air refractive index fluctuation. For avoiding sensing signal fading and perturbations from circumstance during signal transmission, the phase generated carrier is used. The turbulence induced air refractive index fluctuations are demodulated by the algorithm of correlation. Background noise of the sensor is below10⁻¹⁷ . By comparing with the refractive index structure constant measured by fine-wire resistance thermometer, results show good agreement in both their magnitude and tendency. For its outstanding property of corrosion protection, the sensor is especially suitable for maritime atmospheric optical turbulence research, which is verified by one month sea beach investigation. Some results of the maritime optical turbulence intensity are reported in the end.

Current research on modeling of fiber optic gyroscope (FOG) is mainly concentrate on single digital closed loop FOG under square-wave modulation and demodulation. Little work has been done in modeling and simulation of the second feedback loop of FOG under four-state modulation and demodulation. However, the second feedback loop is very important in improving FOG performance. In order to improve the accuracy and stability more efficient, it’s essential to modeling and does simulation of the second feedback loop for fiber optic gyroscope especially in the field of high precision application. There are three major contributions in this paper. Firstly, the physical model of digital closed loop fiber optic gyroscope is built and the scale factor error of FOG due to gain error is derived in theory. The gain error including half-wave voltage change and driver circuit gain change are mainly caused by temperature fluctuation in practical environment. To solve this problem, the second feedback loop based on four-state modulation and demodulation method is provided, and the control model of this method is then set up theoretically by means of transfer function. In the end, simulation of the second feedback loop of FOG is performed by Labview to demonstrate the efficiency of this method. According to our theoretical analysis of the control model and the simulation result, this method can track and compensate the variation of driver circuit gain and half-wave voltage in real-time. Therefore, the nonlinear error of FOG scale factor is reduced by the control of the second feedback loop, which leads to improvement of FOG accuracy.

In this paper, a novel density sensor based on high-birefringence fiber loop mirror is proposed and studied. The high-birefringence fiber is pasted to a ring shaped rubber gasbag and placed in the liquid. Fasten the gasbag to the bottom of the container. When the density of liquid is changed, the liquid level keeps the same. The change of the pressure outside the gasbag leads to the variation of the volume of the air in the gasbag. Eventually, the strain of high-birefringence fiber varies with the variation of the volume of the air and the transmittance of high-birefringence fiber loop mirror shifts with the density change. The experimental result indicates that the shifts of wavelengths are in good linear relationship with the density of liquid. The experiment shows that the sensitivity is 8.024nm/(kg/m³). The novel density sensor has the advantages such as high sensitivity, polarization independent, low cost and good repeatability.

Fiber-Optic Gyroscope (FOG) scale factor nonlinear error will result in errors in Strapdown Inertial Navigation System (SINS). In order to reduce nonlinear error of FOG scale factor in SINS, a compensation method is proposed in this paper based on curve piecewise fitting of FOG output. Firstly, reasons which can result in FOG scale factor error are introduced and the definition of nonlinear degree is provided. Then we introduce the method to divide the output range of FOG into several small pieces, and curve fitting is performed in each output range of FOG to obtain scale factor parameter. Different scale factor parameters of FOG are used in different pieces to improve FOG output precision. These parameters are identified by using three-axis turntable, and nonlinear error of FOG scale factor can be reduced. Finally, three-axis swing experiment of SINS verifies that the proposed method can reduce attitude output errors of SINS by compensating the nonlinear error of FOG scale factor and improve the precision of navigation. The results of experiments also demonstrate that the compensation scheme is easy to implement. It can effectively compensate the nonlinear error of FOG scale factor with slightly increased computation complexity. This method can be used in inertial technology based on FOG to improve precision.

This paper introduces a new kind of electronic product — Package Security Recorder of Vibration. It utilizes STC89C54RD+ LQFP-44 MCU as its main controller. At the same time, it also utilizes Freescale MMA845A 3-Axis 8-bit/12-bit Digital Accelerometer and Maxim DS1302 Trickle Charge Timekeeping Chip. It utilizes the MCU to read the value of the accelerometer and the value of the timekeeping chip, and records the data into the inner E²PROM of MCU. The whole device achieves measuring, reading and recording the time of the vibration and the intensity of the vibration. When we need the data, we can read them out. The data can be used in analyzing the condition of the cargo when it transported. The device can be applied to monitor the security of package. It solves the problem of responsibility affirming, when the valuable cargo are damaged while it transported. It offers powerful safeguard for the package. It’s very value for application.

A selective-filling technique was demonstrated to improve the optical properties of photonic crystal fibres (PCFs). Such a technique can be used to fill one or more fluid samples selectively into desired air holes. The technique is based on drilling a hole or carving a groove on the surface of a PCF to expose selected air holes to atmosphere by the use of a micromachining system comprising of a femtosecond infrared laser and a microscope. The exposed section was immersed into a fluid and the air holes are then filled through the well-known capillarity action. Provided two or more grooves are fabricated on different locations and different orientation along the fibre surface, different fluids may be filled into different airholes to form a hybrid fibre. As an example, we filled half of a pure-silica PCF by a fluid with n=1.480 by carving a rectangular groove on the fibre. Consequently, the half-filled PCF became a bandgap-guiding structure (upper half), resulted from a higher refractive index in the fluid rods than in the fibre core, and three bandgaps were observed within the wavelength range from 600 to 1700 nm. Whereas, the lower half (unfilled holes) of the fibre remains an air/silica index-guiding structure. When the hybrid PCF is bent, its bandgaps gradually narrowed, resulted from the shifts of the bandgap edges. The bandgap edges had distinct bend-sensitivities when the hybrid PCF was bent toward different directions. Especially, the bandgaps are hardly affected when the half-filled PCF was bent toward the fluid-filled region. Such unique bend properties could be used to monitor simultaneously the bend directions and the curvature of the engineering structures.

The paper conducts a research on a new type of long period fiber grating with a local micro-structured defect, we analyze and simulate its spectral characteristics by the coupled mode theory and transfer matrix method. Gaining this new type of long period fiber grating method is etching a long period fiber grating by the hydrofluoric acid (HF). This method will etch the local couple of long period fiber grating. The result shows that with the change of the etching depth, length and the position of the defect state, it will open a transmission window and break up into two transmission peaks in the spectra of the stop-band of long period fiber grating, the depth of the two transmission peaks have some relationship with the etching depth, length and the position of the defect state. When the corrosion depth is shallow, the depth of the left peak is higher than the right peak, with the increase of the corrosion depth, the depth of right peak gradually is increasing and over the left peak, the two peaks will return to the state of a single peak, if the corrosion depth continues to increase. With the increase in the length of the corrosion, the depth of the left transmission peak is greater than the right peak, with the continued increase of the corrosion length, the right peak’s depth will gradually increase and over the left peak, if the corrosion length continues to increase, showing that the depth of the two peaks are equal, however, compared with previous cycles the transmission peaks depth decreases. With the change of the corrosion position L_TH off the center, the transmittance of the peak’s depth gradually decreases. This research offers a theoretical basis for making the new type of local micro-structured long period fiber grating and achieving double parameters sensing applications.

A novel composite interferometer sensor is presented and its sensing characteristics are investigated. Based on the infiber integrated Michelson interferometer, a quartz tube is used to encapsulate the ends of the twin-core fiber and single mode fiber to form the dual extrinsic FP cavities. Thereby, the Michelson and FP configurations are integrated into a single fiber, which we call it Michelson-FP composite interferometer sensor. The novel sensor can respond to the axial strain and radial bending simultaneously. We have derived and analyzed the interferometer principle of the new structure. The analysis results show that the interferometer sensor could be considered as the superposition of Michelson interferometer and FP interferometer. Moreover, we establish a testing system and conduct a series of experiments to investigate the strain and bending characteristics. We measure the reflection spectra with the spectrum analyzer. The spectral response of the composite interferometer sensor presents two pattern fringes with different frequencies due to the respective optical path interferometers. The experimental results indicate that the composite interferometer sensor is very sensitive to the strain and bending characteristics, and the presented sensor has different strain and bending sensitivity coefficients. Due to these characteristics, the presented sensor might be able to measure the strain and bending characteristics simultaneously. In conclusion, the presented novel interferometer sensor is of compact structure, high integration and good strain and bending sensing characteristics. Thus, many types of fiber-optic sensors may be built based on it.

A fiber Bragg grating (FBG) sensor packaged with a thin-wall alloy tube for simultaneous measurement of temperature and pressure is proposed. The influence of the structural parameters on the pressure sensitivity is investigated both numerically and experimentally. Experimental results agree well with the simulations. The pressure sensitivities of 7.8 pm/MPa and temperature sensitivity of 20.1 pm/°C are obtained in the measurement range of 0-60 MPa and 0-150°C, respectively. High repeatability and high linearity of the pressure measurement are confirmed by the experiment. By changing the materials with different elastic modulus, the inner diameter and thickness of the alloy tube, the measuring range and sensitivity of the sensor can be further optimized. The sensing performance of the sensor is also compared with a FBG sensor with another packaging structure. Preliminary results indicates that the sensor has good sensing performance and is promising to be used for long-term pressure sensing in harsh environments.

A distributed feedback (DFB) fiber laser is compact, and is very suitable for using as a hydrophone to sense acoustic pressure. A DFB fiber laser hydrophone was researched. In the fiber laser hydrophone signal demodulating system, an unbalanced Michelson fiber interferometer and a Phase Generated Carrier (PGC) method were used. The PGC method can be used to demodulating the acoustic signal from the interference signal. Comparing with the Naval Research Laboratory (NRL) method and Naval Postgraduate School (NPS) method, the digitized PGC method requires a greater amount of computation because of the high signal sampling, but it demands only one interference signal which makes the less fiber connections of the fiber laser hydrophone array. So the fiber laser hydrophone array based on the PGC method has lower complexity and higher reliability than that based on the NRL method or NPS method. The experimental results approve that the PGC method can demodulate acoustic signal between 20~2000 Hz frequency range with good signal-to-noise ratio (SNR) when the PZT driving frequency is 20 kHz.

The core and cladding modes exhibit different refractive index sensitivities, while temperature and stress sensitivities are approximately equal. Because of the characters of cladding mode, the solution refractive index(SRI) sensor is designed and studied. In order to increase the sensitivity of SRI sensor, 45nm thick gold film is deposited on the surface of cladding of TFBG to excite surface plasmon resonance(SPR). The quality and uniformity of gold surface were investigated with aid of a thermal field scanning electron microscopy and the effect is satisfactory. After that, the refractive index(RI) sensing characteristics of both bare and gold deposited TFBGs were studied by experiments of different concentration solutions of NaCl、MgCl2 and CaCl2 respectively. The result proved that the TFBG-SPR increase the RI sensitivity dramatically by 1.5 nm/RIU to 500 nm/RIU. And SRI of TFBG-SPR is 250 to 400 times larger than that of the bare-TFBG. The linear fittings of the center wavelength of cladding modes and SRI of bare and gold-coating deposited SPR sensor are good when refractive index is changed from 1.333 to 1.3941. Meanwhile, the influence of temperature on SPR was taken in consideration and compensated.

The property of polarization is a nature of light. In this paper, the polarization of optical fiber sensor is mainly studied and the control of optical fiber polarization is achieved by using a controller of optical torsion polarization instead of coil type polarization controller. A novel combined optimum type of single-mode fiber interferometer is designed and the expression of output waveform is acquired through theoretical derivation. Accordingly, with MATLAB simulation, it can be analyzed and obtained that while the phase difference between the two arms of the interferometer is Δφ = 90°, the output light is not under the influence of the frequency doubling and it is the most sensitive at this moment . The performance of the developed optical fiber sensor system which is composed by the combined interferometer is verified by a preliminary test that we generate the AE (acoustic emission )signals by knocking a piece of marble slab, then the AE signals could be detected by the system. The test results demonstrate that the developed fiber-optic sensors have emerged as effective means of detecting AE signals, which solves the polarization fade-out problem using a controller of optical torsion polarization, then the output signals could be achieved with higher visibility.

In this paper, a kind of special optical fiber bonding high-temperature aging plan is raised. The armored optical fiber technology is applied to guarantee the long-term stability of the optical properties of the standard instrument itself. The temperature compensation encapsulation technology is adopted for optical fiber grating, that is, the wavelength will remain constant under the standard atmosphere pressure and chamber temperature. It becomes the optical fiber grating sensing wavelength standard instrument. The optical fiber grating standard instrument based upon this kind of new-type structure is tested, and the result has its word that the temperature shift of this optical fiber grating standard instrument after encapsulation is less than 0.5pm/℃. Coupled with the simple temperature control, the wavelength accuracy of the optical fiber grating standard instrument will be controlled below ±1pm and its long-term stability will be smaller than 2pm/℃. Differ from F-P standard instrument, this optical fiber grating standard instrument is one without mechanical device and is purely physical. So, it features more reliable performance and is applicable to mass production. The costs of this kind of optical fiber grating standard instrument is under control and will see an important application in the optical fiber grating sensing technology.

A novel Cantilever-based two-axis FBG accelerometer (FBGA) is presented. By installing two fiber Bragg gratings on the cantilever, the proposed FBGA can detect the acceleration, both its magnitude and direction. Theoretical analyses including acceleration response and natural frequency are given. The experimental results show an acceleration sensitivity of 40 pm/g in the X-axis, 18 pm/g in the Y-axis, a directivity of better than 20 dB, and a natural frequency of about 100 Hz. These results agree well with theoretical expectations.

The relations and correlation coefficients (CCs) between the OCT signal and the modified state entropy (MSE) of electroencephalogram (EEG) have been studied. Three dimensional (3D) OCT images of rat brains through the thinned skull and EEG have been measured simultaneously anesthetizing to reduce brain activity with the quadrature fringe widefield OCT. Measured 3D volumes are 4mm × 4mm × 2.8mm (Depth). MSE is the product of state entropy of EEG and its effective value. Depth profiles were obtained at the selected three points on the surface of thinned skull. For chosen each depth, the relative signal intensity (RSI) is defined as the ratios of signal intensity to first signal intensity. Deepening the anesthesia RSI increased and MSE decreased to show negative correlation and CCs from -0.31 to -0.56. These results indicate enhancements of the feasibility of OCT as a tool for monitoring/diagnosing the brain tissue viability.

The polarization maintaining fiber has been playing an important role in the fields of optical fiber sensing, communication, and so on. The beat length is one of the main parameters of polarization maintaining fiber, and it usually represents its polarization maintaining performance. In this paper, the beat length variation of Panda fiber with external force is investigated. The simulation results indicate that the beat length variation was determined both by the external force value F and the angle θ between the external force direction and the slow axis of Panda fiber. When F is a constant, the beat length of polarization maintaining fiber is changed in sinusoidal form whose various cycle is π with the variation of θ. Meanwhile, the minimum and maximum values of beat length will be obtained when the angles are even multiple of π/2 or odd multiple of π/2, respectively. When θ is a constant, the beat length is changed in linear form with the increasing of external force value. Finally, the experimental system of beat length measurement based on Sagnac interferometer loop is illustrated, and the result shows an excellent agreement with the theoretical analysis.

Heat transfer is very complicate in fusion splicing process of photonic crystal fibers (PCFs) due to different structures and sizes of air hole, which requires different fusion splicing power and offsets of heat source. Based on the heat transfer characteristics, this paper focus on the optimal splicing offset splicing the single mode fiber and PCFs with a CO₂ laser irradiation. The theory and experiments both show that the research results can effectively calculate the optimal fusion splicing offset and guide the practical splicing between PCFs and SMFs.

The development of sensitive fiber-optic accelerometers is a subject of continuing interest. To acquire high resolution, Michelson phase interferometric techniques are widely adopted. Among the variety structures, the compliant cylinder approach is particularly attractive due to its high sensitivity that is defined as the induced phase shift per applied acceleration. While the two arms of Michelson interferometer should be at the same optical path, it is inconvenient to adjust the two arms’ length to equal, also the polarization instability and phase random drift will cause a signal decline. To overcome these limitations, a novel optical fiber accelerometer based on differential interferometric techniques is proposed and investigated. The interferometer is a Sagnac-like white light interferometer, which means the bandwidth of laser spectrum can be as wide as tens nanometers. This interferometer was firstly reported by Levin in 1990s. Lights are divided to two paths before entering the coupler. To induce time difference, one passes through a delay arm and another goes a direct arm. After modulated by the sensing component, they reflect to opposite arm. The sensing part is formed by a seismic mass that is held to only one compliant cylinder, where the single-mode optical fiber is wrapped tightly. When sticking to vibrations, the cylinder compresses or stretches as a spring. The corresponding changes in cylinder circumference lead to strain in the sensing fibers, which is detected as an optical phase shift by the interferometer. The lights from two arms reach the vibration source at different time, sensing a different accelerate speed; produce a different optic path difference. Integrating the dissimilarity of the accelerated speed by time can obtain the total acceleration graph. A shaker’s vibration has been tested by the proposed accelerometer referring to a standard piezoelectric accelerometer. A 99.8% linearity of the optical phase shift to the ground acceleration is achieved. The acceleration sensitivity is 300 rad/g. It proves to have a simple structure, good practice, reliable measurement and stable performance.

Optical Coherence Tomography (OCT) was successfully applied in the microstructure imaging of biological tissue after being proposed firstly in 1991 by the researchers of MIT. As a novel optical imaging technology, it mainly uses interference principles to achieve noninvasive and high resolution visualization of samples. OCT works analogously to an ultrasound scanner, the major difference is that ultrasound pulses are replaced by broadband light. According to whether need for mechanical axial scan in the depth direction, it can be classified into the time-domain OCT (TD-OCT) and frequency-domain OCT (FD-OCT). The FD-OCT system overmatches the TD-OCT in imaging speed because of its depth collection advantage. But in the reconstructive image of FD-OCT detection, the complex-conjugate ambiguity will seriously deteriorate the imaging effect of tomogram. So the technique of removing the complex-conjugate image is employed that is called complex FD-OCT. The complex FD-OCT has widely application in many fields, especially in the refractive index measurement. The refractive index is an important parameter characterizing light propagation in the medium. In the paper, we present a method to measure the average refractive index of the sample with substrate calibration by using complex FD-OCT method, in which we can calculate it without depending on the parameters of system such as spectral width of light source. Due to the measurement of average refractive index relative to the actual thickness and optical length, it is necessary to obtain them of the sample experimentally. The complex FD-OCT method can easily achieved the optical length via measuring the positions of the sample’s front and rear surfaces. In the experiment, the coverslip (the borosilicate glass) is chosen as the sample and the calibration substrate. We make use of the substrate to load the sample on it, and then the tomogram of the sample can be achieved by means of OCT’s lateral scan in the edge of the sample and complex FD-OCT method. According to the experimental results, we can acquire the sample’s tomographic information and position of the substrate. The ratio of actual thickness and optical length can be indirectly calculated out with the pixel number obtained by analyzing the image data. So with only one time scan, we can complete the measurement of average refractive index of the sample without aid of other instruments.

As a class of hollow core photonic bandgap fiber (HC-PBGF), hollow core Bragg fibers (HC-BFs) with broadband transmission for multi-component trace-gas sensing have attracted much interest in recent years. In this paper, we numerically investigate the PBG characteristics of HC-BFs with the conventional periodic cladding (CPC) and with our previously proposed linearly-chirped cladding (LCC). The results show that the LCC structure is more suitable for broadening the omnidirectional PBG (OPBG) range by regulating the linear increment of cladding period or the layer number, which provide us with more degrees of freedom for designing a broadband HC-BF. Based on that, an optimized Te/PS (tellurium/polystyrene)-based HC-BF with the LCC for the wavelength range of OPBG covering the whole range of 3 to 5μm is designed. Moreover, by using the ray-optics method, the transmission loss of HE11 mode is also calculated, verifying the feasibility of the Te/PS-based LCC with mid-infrared broadband low-loss transmission ranging from 3 to 5μm.

A novel all-fiber vibration velocity measurement system with high contrast of interfering fringes is proposed and demonstrated. The configuration utilizes polarization beam splitters to remove the unwanted reflected light beams. With a shaker vibration measurement experiment, it is shown that the system can successfully improve the interfering fringe contrast to 69.8% significantly and the results can be better if there is no counter reflecting light in 3×3 coupler. The system is also convenient in free-surface velocity measurement application of the shock wave and the experiment achieves long time measurement (700μs) in strong disturbance.

A type of Michelson interferometer with two optical fiber loop reflectors acoustic emission sensor is proposed in the article to detect the vibrations produced by ultrasonic waves propagating in a solid body. Two optical fiber loop reflectors are equivalent to the sensing arm and the reference arm instead of traditional Michelson interferometer end reflecter Theoretical analyses indicate that the sensitivity of the system has been remarkably increased because of the decrease of the losses of light energy. The best operating point of optical fiber sensor is fixed by theoretical derivation and simulation of computer, and the signal frequency which is detected by the sensor is the frequency of input signal. PZT (Piezoelectric Ceramic) is powered by signal generator as known ultrasonic source, The Polarization controller is used to make the reflected light interference，The fiber length is changed by adjusting the DC voltage on the PZT with the fiber loop to make the sensor system response that ΔΦ is closed to π/2. the signal basis frequency detected by the sensor is the frequency of the input signal. Then impacts the surface of the marble slab with home-made mechanical acoustic emission source. And detect it. and then the frequency characteristic of acoustic emission signal is obtained by Fourier technique. The experimental results indicate that the system can identify the frequency characteristic of acoustic emission signal, and it can be also used to detect the surface feeble vibration which is generated by ultrasonic waves propagating in material structure.

Pulse polarization switching is an important new method to eliminate the polarization-induced fading (PIF) in the interferometric fiber sensing system. An integrated Ti-indiffused LiNbO3 Mach–Zehnder modulator is used to achieve high-speed switch of the polarization state by switching the voltage between two appropriate voltages applied to the modulator. The stability of the polarization switching is affected by environmental factors, especially the temperature. In this paper, the stability of the polarization switching is studied. Firstly, the structure of the modulator and the principle of the polarization switching are introduced. Secondly, a feedback control method to overcome the switch instability is proposed. The output polarization state could be obtained by monitoring the intensity of the output light. Finally, the high-speed and high-accuracy stable switching between two orthogonal polarization states is realized using this method and experimentally demonstrated.

The mutual restriction relationship between the acceleration sensitivity and the resonant frequency blocked the improvement of the performance of the common fiber optic F-P accelerometer. A new type of optic fiber accelerometer based on the folding F-P cavity was introduced in this article. The phase changes caused by a certain acceleration signal are amplified through the multiple reflections of the light in the F-P cavity. Since the optical structure has no effects on the resonance frequency of the system, the acceleration sensitivity can be improved while the resonance frequency remains unchanged. The theoretical sensitivity and resonant frequency are analyzed. A collimator lens with the gradient index fiber is used to reduce the losses of the longitudinal displacement in the F-P cavity. The results show that the improvement of the sensitivity is directly proportional to the times of reflections of the light in the cavity. The theoretical sensitivity can reach 26~30dB 30dB while the resonant frequency of the accelerometer is kept at 800Hz

Melamine is an insalubrious chemical, and has been frequently added into milk products illegally, to make the products more protein-rich. However, it can cause some various diseases, such as kidney stones and bladder cancer. In this paper, a novel optical fiber sensor with high sensitivity based on absorption of the evanescent field for melamine detection is successfully proposed and developed. Different concentrations of melamine changing from 0 to 10mg/mL have been detected using the micro/nano-sensing fiber decorated with silver nanoparticles cluster layer. As the concentration increases, the sensing fiber’s output intensity gradually deceases and the absorption of the analyte becomes large. The concentration changing of 1mg/ml can cause the absorbance varying 0.664 and the limit of the melamine detectable concentration is 1ug/mL. Besides, the coupling properties between silver nanoparticles have also been analyzed by the FDTD method. Overall, this evanescent field enhanced optical fiber sensor has potential to be used in oligo-analyte detection and will promote the development of biomolecular and chemical sensing applications.

We have fabricated a novel microfluidic chip based on fiber sensor with casting PDMS method. The optical fiber is used to transmit excitation light, so the diameter of the excitation beam is decreased to 93μm. In order to improve the coupling efficiency of the excitation light in the fiber, the optical fiber collimation device is used to couple beam. The microfluidic chip consists of multimode optical fiber, PDMS cover slab and PDMS base slab. The mould of cover slab is made through twice exposal, however the base slab is achieved using once exposal only. The depths of microfluidic channel and optical fiber channel in the PDMS cover slab are 50μm and 90μm, respectively, and the optical fiber channel in the PDMS base slab is only 40μm. This design can make the centers of the microfluidic channel and the fiber channel in the same point, so the microfluidic channel and the optical fiber can be aimed at easily. In addition, the size of microfluidic channel depth is near the size of light spot of optical fiber, so the detection sensitivity is improved without using the optical focusing system. The detection system of the microfluidic chip is manufactured and it composed of high voltage modules, darkroom, LED light source, photomultiplier and data acquisition circuit, moreover, the software of the detection system is developed. The high voltage modules with four 2kV are used to control the sample amount in the separation channel, so the sensitivity is improved. The microfluidic chip is placed in the darkroom to avoid the interference of external light. The high brightness blue light emitting diode (LED) is used as excitation light sources for inducing fluorescence detection through coupling the LED light into the optical fiber. The photomultiplier is used to amplify the fluorescence signals and the function of data acquisition circuit is data collection and data processing. Under the control of software, the experiment process can be implemented easily. As an application, the microfluidic chip is tested on the detection system for the separation experiment of FITC fluorescein and FITC-labeled amino acid. The experiments justify the feasibility of the chip.

In this presentation, fibers with 2 and 3 layers of coatings are made and their sound sensitivities are tested. It’s found that the interface between coating layers could weaken the acoustic transmission, and the acoustic impedance is mainly due to the difference of coating material’s density and velocity of sound. The fiber with 1.0mm diameter has the highest sound sensitivity of about 6×10^-12/dyn/cm² when commercially available coating material used. This paper also discusses the method of testing, including how to process the fiber and how to wind fiber. In the end of this contribution, some coating materials and coating diameters are compared.

The measurement accuracy of polarization cross-coupling strength based on white-light interferometry obviously decreases in long-distance polarization maintaining fiber (PMF), due to the difference of dispersion between two eigenmodes (birefringence dispersion). In this paper, we demonstrate a bidirectional measurement method with the scheme including a polarization maintaining coupler, a magnetic optical circulator and an Optical Coherence Domain Polarimeter (OCDP). The experiment setup and results are described in detail. The cross-coupling distribution results from each direction measurement were processed to mitigate the influence of dispersion. The compensation is conducted on coupling strength results, instead of raw interference signal in traditional method. The method saves the investigation of birefringence dispersion coefficient and light source parameters compared with compensation in frequency domain. Our experiment with a PMF coil of 200m length demonstrates the effectiveness in improving strength accuracy with absolute deviation less than 0.31dB, and spatial resolution recovered to 8.4cm.

In this paper, we study the birefringence of polymer photonic crystal fibers with elliptical air holes and squeezed triangular lattice in the cladding. We use the modified squeezing ratio to describe the squeezed degree reduced by both squeezed lattice and elliptical air holes. By using the supercell lattice method, the study on the influence of the squeezing on the birefringence of photonic crystal fibers is given. Studies show that the birefringence on the order of 10^-3 can be easily achieved. Based on these numerical simulations, it is noted that a simple function is given to express the relation between birefringence and the modified squeezing ratio of polymer photonic crystal fibers in a certain range.

By assuming that the light coupled into a single-mode fiber is monochromatic generated by the diffused far field , employing the lens coupling theory and van Cittert-Zernike theorem，we obtain the general expressions of the coupling efficiency of an optical fiber. This subject focuses on the analysis that the incident light is plane wave; we obtain the F number of coupling lens, which provides the theory support for the design of the coupling lens, corresponding to the optimum coupling efficiency. Fiber coupling efficiency is not only related to the mode matching of incident light and the fiber; the optical axis, the symmetrical axis of lens and the fiber center line misalignment also affect. Simulation results of misalignment errors show that the defocus alignment has little effect on the coupling efficiency, while the effect of both lateral alignment error and angle offset on the coupling efficiency is relatively large.

In this paper, we investigate the dispersion and polarization properties of polymer photonic crystal fiber with elliptical air holes and squeezed lattice using supercell lattice method. We introduce the modified squeezing ratio to describe the squeezed degree reduced by both squeezed lattice and elliptical air holes. Based on the supercell lattice method, the highly birefringence and flattened chromatic dispersion can be obtained as the structure parameters of polymer photonic crystal fiber are appropriate simultaneously.

Acceleration measurement plays an important role in a variety of fields in science and engineering. In particular, the accurate, continuous and non-contact recording of the shock acceleration profiles of the free target surfaces is considered as a critical technique in shock physics. Various kinds of optical interferometers have been developed to monitor the motion of the surfaces of shocked targets since the 1960s, for instance, the velocity interferometer system for any reflector, the fiber optic accelerometer, the photonic Doppler velocimetry system and the displacement interferometer. However, most of such systems rely on the coherent quasi-monochromatic illumination and discrete optic elements, which are costly in setting-up and maintenance. In 1996, L. Levin et al reported an interferometric fiber-optic Doppler velocimeter with high-dynamic range, in which fiber-coupled components were used to replace the discrete optic elements. However, the fringe visibility of the Levin’s system is low because of the coupled components, which greatly limits the reliability and accuracy in the shock measurement. In this paper, a compact all-fiber interferometer system for measuring the shock acceleration is developed and tested. The advantage of the system is that not only removes the non-interfering light and enhances the fringe visibility, but also reduces polarization induced signal fading and the polarization induced phase shift. Moreover, it also does not require a source of long coherence length. The system bases entirely on single-mode fiber optics and mainly consists of a polarization beam splitter, a faraday rotator, a depolarizer and a 3×3 single-mode fiber coupler which work at 1310 nm wavelength. The optical systems of the interferometer are described and the experimental results compared with a shock acceleration calibration system with a pneumatic exciter (PneuShock^TM Model 9525C by The Modal Shop) are reported. In the shock acceleration test, the interferometer system measured shock acceleration with peak accelerations of ~100,000 m/s² and the durations of ~0.2 ms which are conformed to the results of the shock acceleration calibration system. The measured relative error of the acceleration is within 3%.

An inter-mode interference sensor based on biconical taped micro/nano optical fibers is presented. And the structural parameters of the sensor are optimized. The device sensitivity has been simulated by the finite element method with commercial software.

The long distance fiber-optic sensing system based on Mach-Zehnder interferometer has been widely used in many fields. We discussed the polarization signal fading caused by the birefringence property of the fiber. Research results show that, due to the birefringence effect of long distance fiber-optic sensing, when incident light polarization state changes, the output power will change which causing interference signal changes. This phenomenon is called "polarization-induced signal fading ". In order to eliminate polarization fading in long distance fiber-optic sensing, add the system with polarization controller to adjust light polarization state, can get a good visibility of interference signal.

In this paper we present a frequency multiplexed optical coherence tomography imaging method in which simultaneous data acquisition is enabled by a multiplexer. The multiplexer is based on a pair of Bragg cells, simultaneously driven at several frequencies that enable multiple paths in the reference arm. Multiple beams are created in the multiplexer and then recombined again so that the resulting beam multiplex can be inserted into a single mode fiber. In this paper we discuss the design principles for a multiplexer that supports the reflectivity measurements as well as polarization sensitive imaging at several different depths. We show how to design a system with a low footprint, while allowing broad optical bandwidth to be used for imaging in multiple channels with little crosstalk between adjacent channels.

Current research on photonic crystal fiber (PCF) for acoustic sensing was focused on the PCF’s pressure sensitivity enhancement. However, whether the enhancement of the PCF’s pressure sensitivity can be actually realized is still controversial. Practical hydrophone, utilizing PCFs, to manifest its superior sensitivity to normal single mode fibers (SMFs) for acoustic sensing, should be made. Account to this point of view, actual hydrophone was fabricated. Index guiding PCF was used, the fiber core is solid silicon dioxide (SiO₂), and the cladding is SiO₂ filled with lots of periodical transverse circular air hollows. The PCF, mounted on an air-backed mandrel for structural sensitivity enhancement, was used as a sensing arm of the fiber Michelson interferometer. The other arm, so called reference arm, was made of SMF. Faraday rotator mirrors (FRM) were spliced in the end of each interferometric arm account for polarization induced phase fading, which is a common scheme in fiber interferometric sensing systems. A similar hydrophone, with all the same structure except that the PCF was exchanged into SMF, was also fabrication to make the contrast. The narrowlinewidth and frequency-tunable optical fiber laser was used to achieve high accuracy optical interferometric measurement. Meanwhile, the phase generated carrier (PGC) modulation-demodulation scheme was adopted to interrogate the measurand signal. Experiment was done by using acoustic standing-wave test apparatus. Linearity characteristics of the two hydrophones were measured at frequency 100Hz, 500Hz, and 1000Hz, experimental results showed that the maximum error of the linearity was 10%, a little larger than the theoretical results. Pressure sensitivities of the PCF hydrophone and the SMF hydrophone were measured using a reference standard PZT hydrophone in the frequency range from 20 Hz to 1600 Hz, the measurement data showed that the sensitivity of the PCF hydrophone was about -162.8 dB re. rad/μPa, with a fluctuation ±1.3 dB over the whole measured frequency range, compared with the sensitivity of -163.6 dB re. rad/μPa and a almost the same fluctuation of the SMF hydrophone. The contrast result shown that the sensitivity of the PCF hydrophone is only a little larger than that of the SMF hydrophone, the reason was that the structure sensitivity enhancement played a weightier role in pressure sensitivity.

This paper investigates the effects of fiber bundle on the performance of Full-field swept source OCT (FFSS-OCT) in terms of depth range, depth resolution and transversal resolution. A superfast CMOS camera with full sensor resolution 1024 x 1024 pixels and 60 kHz in maximum frame rate is employed in the testing system. A fiber bundle which contains 18000 single fibers is used to transmit images from interference beam to the camera. Depth range and resolution are assessed by varying optical path difference (OPD) between object arm and reference arm. The operation is repeated under a set of frame rates from 1 kHz to 3 kHz. In addition, an USAF plate is used as a planar object to test transversal resolution. For comparison, above parameters are tested as well with a bulk-optic setup which is built under the same system configuration but without bundle. The results show that the difference between performances of bundle and Bulkoptic setups is not remarkable. As a practical example, 3D profile of a coin is measured using two setups. In sum, this investigation shows that the performance of bundle setup can compete with that of bulk-optic setup in implementing FFSS-OCT. The quantitative results are helpful for researchers to incorporate bundles to FFSS-OCT systems in future.

This paper researches the signal conditioning program of optical voltage/current transformer and the imbalance during the transmission of dual optical path, gives a brief introduction to the basic principle of optical voltage transformer based on electro-optic Pockels effect and optical current transformer based on Faraday Magnetic-optical Effect, and induces a general expression form of output light intensities This paper research on the signal modulation methods for the system: AC and DC modulations. What is more, the advantages and disadvantages of both modulations in the system will be analyzed. Considering the characteristics that the systematic noise and signal have the spectrum overlapping and that when there is any fault, the fact that in the small signal detection system the output SNR of AC modulation is better than that of DC modulation will be proved. For the parameter changes caused by the environment factors, the feedback control linked by the DSP is imported, it automatically adjusts the balance of the two branch parameters, acquires the measured component in the condition of the two branch unbalance parameters. Furthermore, this paper researches on the influence of imbalance of the dual optical path on the signal detection system. It analyzes the error characteristics due to different kinds of losses and to component matching disorders and other intrinsic factors and then put forward the method to calculate balancing factors by means of the RMS of 50Hz signal. The result proves that using this method can improve the output SNR of optical voltage/current transformer to some extent.

In this report, we demonstrate characteristics and parameters of a coherence-gated Shack-Hartmann wavefront sensor (CG/SH-WFS) that is capable of measuring depth-resolved wavefront aberrations. A technique of dynamic centroiding is applied to CG/SH-WFS images and its precision is evaluated. The performance of the CG/SH-WFS system is compared with a commercial SH-WFS measuring a reflective surface. Real-time wavefront measurements from a scattering sample are also presented. The experiments demonstrate that the performance of CG/SH-WFS can replace conventional SHWFS and also provide its unique advantages.

The materials used to fabricate scaffolds for tissue engineering are derived from synthetic polymers, mainly from the polyester family, or from natural materials (e.g., collagen and chitosan). The mechanical properties and the structural properties of these materials can be tailored by adjusting the molecular weight, the crystalline state, and the ratio of monomers in the copolymers. Quality control and adjustment of the scaffold manufacturing process are essential to achieve high standard scaffolds. Most scaffolds are made from highly crystalline polymers, which inevitably result in their opaque appearance. Their 3-D opaque structure prevents the observation of internal uneven surface structures of the scaffolds under normal optical instruments, such as the traditional light microscope. The inability to easily monitor the inner structure of scaffolds as well as the interface with the old bone poses a major challenge for tissue engineering: it impedes the precise control and adjustment of the parameters that affect the cell growth in response to various mimicked culture conditions. The aim of this paper is to investigate the interface between the femur rat bone and the new bone that is obtained using a method of tissue engineering that is based on different artificial matrixes inserted in previously artificially induced defects. For this study, 15 rats were used in conformity with ethical procedures. In all the femurs a round defect was induced by drilling with a 1 mm spherical Co-Cr surgical drill. The matrixes used were Bioss and 4bone. These materials were inserted into the induced defects. The femurs were investigated at 1 week, 1 month, 2 month and three month after the surgical procedures. The interfaces were examined using Time Domain (TD) Optical Coherence Tomography (OCT) combined with Confocal Microscopy (CM). The optical configuration uses two single mode directional couplers with a superluminiscent diode as the source centered at 1300 nm. The scanning procedure is similar to that used in any CM, where the fast scanning is en-face (line rate) and the scanning in depth is much slower (at the frame rate). The results showed open interfaces due to the insufficient healing process, as well as closed interfaces due to a new bone formation inside the defect. The conclusion of this study is that TD-OCT can act as a valuable tool in the investigation of the interface between the old bone and the one that has been newly induced due to the osteoinductive process.