A measurement method of distributed birefringence dispersion (BD) for polarization-maintaining fiber is presented. This method is based on white light interferometry and optimization method. The sharpness function proposed in this paper is theoretically proved that will reach its maximum at the proper BD value. In addition, it is robust to noise demonstrated via simulation experiment. Eventually, the measurement result of average distributed BD for a 500m-long PMF coil with splicing points is -392.6 fs2/m and the relative error for every splicing point is less than 0.5‰.
The subject of this work is the strain characteristic of fiber-optic flexural disk accelerometer. In the presented investigation, the strain distribution of flexural disk is studied and the result shows that the position of fiber coil has a significant effect on the strain of fiber coil. We simulated the strain distribution of fiber-optic flexural disk accelerometer that based on multilayer fiber coils and on the optimized position. In experiment, corresponding sample accelerometer is fabricated and tested in the Brillouin Optical Time-Domain Analysis. The experimental result is in good agreement with the simulated result, provides this theoretical approach is effective in designing the fiber-optic flexural disk accelerometer.
We propose an improved optical coherence domain polarimetry (OCDP) calibration scheme by using polarization mode crosstalk (PMC). The scheme can be used to calibrate the OCDP system's measurement result about intensity of PMC. The intensity of 1st order PMCs are measured by polarization extinction ratio (PER) meter as the scale to transfer the standard into OCDP system, and the higher order PMCs formed by 1st orders are used to expand the scale. Specifying alignment angle of joint points and analyzer, we successfully use 3rd order PMCs and expand the range of calibration over -100 dB.
We present a method for measuring polarization extinction ratio (PER) of multi-functional integrated optic chip (MFIOC) based on White light interferometry (WLI) against birefringence dispersion (BD) and noise. Instead of reading peak value, this method obtains PER via calculating the energy of the interferogram, which is theoretically proved that is independent of BD and proportional to the square of its peak value. In addition, the results of simulation demonstrate the method has an advantage of noise robustness versus the conventional peak value method. Eventually, experiment results of 100 measurements for a MFIOC are agree with the theory and simulation results.
In this paper, we propose an improved method of phase generated carrier (PGC) combined with 3×3 coupler to extend dynamic range and compensate low-frequency drift of modulation depth. The small amplitude signal(≤10-2 rad) is figured out by the PGC method to keep the minimum phase resolution and the large amplitude signal(≥10rad) can be calculated by the 3×3 fixed phase difference algorithm to extend the maximum amplitude of the dynamic range. We can get the same result to the signal with the normal amplitude(10-2 rad≤D≤10rad) by any two kinds of methods. Furthermore, the modulation carrier wave amplitude and frequency information can be monitored by the 3×3 auxiliary algorithm to compensate low-frequency drift of modulation depth and keep the system stability as a feedback. According to the result, the interferometer is able to resolve 2.0 ×10-5 rad/√Hz with a dynamic range of 182.2dB@10Hz frequency and 2Mbps sample rates.
This paper proposed a calibration scheme of optical path correlator(OPC) for optical coherence domain polarimeter (OCDP), the calibration scheme employs a dual Mach-Zehnder interferometers multiplexing one OPC by dual wavelength wave division multiplexer, one interferometer as target interferometer is used to sensing measurement, another interferometer with 3×3 coupler as reference interferometer is used for OPC scan speed and positon calibration to improve the target interferometer signal-to-noise ratio(SNR) and interference envelope positioning accuracy, this calibration scheme is used OCDP to measure polarization crosstalk, the experimental results show that SNR is achieved 95dB and the polarization crosstalk position accuracy is achieved submicron.
We present a method to measure the polarization mode dispersion (PMD) of the LiNbO3 multifunctional integrated waveguide modulator (MFIWM) which is consist of a Y-waveguide, two extended polarization maintaining (PM) fibers, lead-in PM pigtail and lead-out PM pigtail. This method is based on an all-fiber time-domain scanning white light interferometer and utilizes fast Fourier transform (FFT) technology to obtain interferometric phase. The PMD of each part of MFIWM was measured and distinguished accurately. It’s demonstrated that, the PMD of Y-waveguide is 13.5 ps/nm/km@1555nm which is approximately 40~160 times of the PMD of PM fibers in the MFIWM under test.
We propose a calibration scheme of the white light interferometer based optical coherence domain polarimetry (OCDP), which could be used to measure the ultra-weak polarization mode crosstalk (PMC) or the ultra-high polarization extinction ratio (PER) of different polarization optical devices. The calibration depends on the first and second order PMC effect of different polarization devices in series. The first and second PMCs between 0 and -90dB, established by five pieces of polarization maintaining fiber (PMF) and a Y-waveguide, is used to prove its feasibility.
In this paper, we present an improved fixed phased demodulation method combined with phase generated carrier (PGC) and ellipse fitting algorithm (EFA) to enhance the phase resolution and suppress the total harmonic distortion (THD) caused by the laser intensity disturbance (LID) of modulation phase. We make the subtraction operation to the outputs of the two 1×2 couplers to get the differential signals without DC offset, which is used to achieve the fixed phase demodulation. The EFA is applied to construct the standard quadrature signals with the two signals. The last output is utilized to finish the small amplitude (<2π rad) demodulation in PGC method, which can increase the phase resolution. The distortion signals caused by the LID effect can be eliminated by the EFA. According to the result, the phase error of the EFA is 0.03rad, the amplitude error is 5% and the phase resolution of system is 2.0×10-6rad/√Hz@1kHz (-106.3dB) with the THD is 5%.
A method of simultaneous evaluation for two branches of a multi-functional integrated optic chip (MFIOC) with a dual channel system is proposed. The difference between the two branches of the MFIOC can be tested simultaneously with a high precision. In the system, the chip is used as a 1×2 splitter and its two branches are combined by a 2×2 coupler. The characteristic peaks of the two branches are distinguished by selecting proper length of the extended fibers which connected to each polarization-maintaining (PM) pigtails. Temperature responses of the two branches of the MFIOC are experimented. Results show that the dual channel system can simultaneously measure the characteristics of the two branches of MFIOC with resolution of over -85 dB and dynamic range of 85dB.
This paper focus on the strain characteristic of the fiber-optic flexural disk accelerometer based on the multilayer sensing fiber coils. The strain state is analyzed in theory, and by using the simulation software, we built the simulation model and obtain the strain distribution of the multilayer sensing fiber coils in different bonding position of the flexural disk. The strain theoretical model agrees well with the strain distribution obtained by the simulation model. According to the results, a flexural disk accelerometer is produced. Experiment results show that the phase sensitivity is 6814rad/g, which is equivalent to the acceleration sensitivity of 15ng/Hz1/2.
A high-sensitivity fiber accelerometer based on multilayer fiber coils is proposed. Acceleration sensing principle of the sensor is analyzed in theory, and with the finite element software, simulation model is built. Two kinds of fiber optic accelerometers with different multilayer fiber coils are designed, and the performance tests are conducted as well. Experimental results show that the sensitivity of accelerometer based on multilayer fiber coils can reach thousands rad/g, and the equivalent transfer coefficient between different layers in multilayer fiber coils is 0.39.
An all-fiber optical coherence domain polarimetry (OCDP) is presented, which can increase the detection sensitivity and dynamic range simultaneously. An all-fiber OCDP system has been built, and the detecting sensitivity of polarization crosstalk can reach -98dB, meanwhile, the dynamic range can keep in 98dB. This method realizes the highest performance of the date OCDP technology, and provides an effective measurement and evaluation tools for high performance fiber optic devices and sensor system.
Online calibration technique for a long-baseline laser interferometer has been studied, which can be used for nanoscale
displacement and vibration measurement. The method combined laser interferometer calibration with measurement to
meet the needs of online calibration and state detection of long-baseline laser interferometer. Based on Phase Generated
Carrier (PGC) demodulation technique, we add a calibration signal which we have already known to phase-modulated
carrier, and according to the amplitude variations of calibration signal, we can achieve work condition monitoring of
laser interferometer and measurement of environmental changes and the instruction of fluctuations. In the paper, a laser
interferometer with 22-meter-long arm, resolution of 20pm and frequency range of DC ~ 200Hz used for displacement
and vibration measurement was constructed, completed the online calibration software and hardware design,
experimental results show that: by adding a calibration signal with frequency of 400Hz, amplitude 600nm, online
condition monitoring of the laser interferometer can be realized. The advantages of this method is,that it can achieve
online calibration for laser interferometer without increase burden in hardware, simplify the interferometer debugging
process, improve operational efficiency, at the same time, it is of great significance and value to practical application of
long-baseline laser interferometer .
A compact fiber optic Michelson interferometer based accelerometer is proposed and demonstrated. In this sensing
system, two optical fibers have been used as the differential sensing element. By way of demodulating the different
optical phase, we can obtain the acceleration which proportional to the initial force applied on the central position
of the two fibers. A simple model has been built to calculate the sensitivity and resonant frequency. The
experimental results show that such an accelerometer has a sensitivity of 0.42rad/g at the resonant frequency
600Hz.
A compact in-fiber integrated fiber-optic Michelson interferometer based accelerometer is proposed and investigated. In
this sensing system, the sensing element consists of a twin-core fiber acting as a bending simple supported beam. By
way of demodulating the optical phase shift, we can obtain the acceleration which proportional to the initial force
applied on the central position of the twin-core fiber. A simple model has been established to calculate the sensitivity and
resonant frequency. The experimental results show that such an accelerometer has a sensitivity of 0.09rad/g at the
resonant frequency of 700Hz.
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