The operation principle of scanning DBR laser was introduced and its multi-channel driving parameters was summarized. Based on FPGA, a multi-channel high-speed and high-precision current drive circuit was designed and fabricated, a scanning laser tuning characteristic testing system was integrated, and parameter control and testing programs were designed to achieve automatic testing. Experimental tests have proven that the developed testing system can well meet the testing requirements of scanning lasers, with a simple structure, high accuracy, and fast speed.
A differential fiber optic gyroscope (FOG) driven by two broadband light sources with different wavelengths was demonstrated theoretically and experimentally, and bias drift and angle random walk both can be reduced considerably due to common-mode error cancellation. A 3-component fiber optic rotational seismometer based on the differential FOG was developed and successfully applied in rotational seismic observation.
The evolution process of characteristic parameters of Fiber Bragg Grating (FBG) during the regeneration process was investigated, and a formation mechanism of regenerated FBG based on non-uniform crystallization in FBG was proposed. The experimental system was built for experimental verification, and the experimental results are consistent with the formation mechanism proposed. The regenerative phenomenon of fibers under different processes, structures, and stress conditions can be well explained with the proposed formation mechanism of regenerated FBG.
The depolarized fiber optic gyroscope (DFOG) uses single-mode fibers (SMFs) to fabricate a depolarized fiber optic coil, which has obvious cost advantages in high sensitivity and precision rotation measurement applications, such as fiber optic rotary seismometers, etc. The depolarized fiber coil assembly (DFCA) is the key component of DFOG, consisting of a SMF coil and at least two polarization maintaining fibers (PMFs) depolarizers. To control the quality of the DFCA, this paper proposes an online evaluation technology for it. A more accurate broad-spectrum light source spectral modulation model is established based on polarization mode interference in the DFCA. The model simulation and experimental testing indicate that the modulated spectrum is a multi-period deep modulated spectrum, and the envelope is the same as the input spectrum. Moreover, the self-coherence curve of the modulated spectrum was calculated, and it contains multiple coherent peaks. It was found that the position and amplitude of self-coherence peaks are determined by the length of PMFs and polarization angular deviation at joint points, respectively. A spectrometer was used to replace the detector of the DFOG and an online testing system for the quality of the DFCA was built and an online evaluation process and algorithm is developed. The exact length of PMFs and angular deviation of depolarizers are obtained. The proposed technology has the advantages of easy implementation and high sensitivity, making it well-suited for monitoring and evaluating the quality of DFCA for an assembled high-precision depolarized FOG.
This paper proposes and demonstrates a practical temperature-insensitive pressure sensor based on the simple reflective birefringence fiber interferometer which consists of only a polarization beam splitter (PBS), two segments of solid core polarization-maintaining photonic crystal fibers (PM-PCFs) with film reflector deposited on the far end of one of the PM-PCFs. We derived its spectrum response equation and the practical temperature insensitive lateral pressure sensor was designed and demonstrated experimentally.
Three types of Fiber Bragg gratings (FBGs) were inscribed in H2-loaded and H2-free fiber with phase mask using 800nm femtosecond (fs) laser, ultraviolet (UV) excimer laser respectively. Their reflection spectra regenerating procedure were observed under different annealing temperature and the models of regeneration process as well as annealing temperature and time were established. Experiments and model fitting show that there were definite regeneration temperature threshold for fs FBGs written in H2-free fiber, H2-loaded fiber and UV FBGs in H2-loaded fiber. The temperature sensing characteristic of RFBGs were investigated and compared experimentally under ultra-wide temperature range.
The transmission spectrum characteristic of two-segment polarization maintaining fibers Sagnac interferometer was investigated and simulated in detail and a temperature-insensitive pressure or strain sensing technology was proposed. An experimental hybrid Sagnac interferometer was built and the solid core polarization maintaining photonic crystal fiber was taken as the sensing probe. The side pressure sensitive coefficients and the temperature crosstalk drift were measured and compared. The experimental results show that the side pressure sensitive coefficient was ~0.2877 nm/N and the temperature drift was less than 0.1 pm/°C.
KEYWORDS: Fiber Bragg gratings, Femtosecond phenomena, Reflectivity, Temperature metrology, Near infrared, Sensors, Ultraviolet radiation, Reflection, Oxygen, Chemical species
We reported a Bragg grating inscribed in gold-coated fiber (FBG) by NIR femtosecond laser (fs) for space application. Gold coating can shield the FBG from ultraviolet radiation and oxygen atom erosion. Cryogenic test, high temperature test, and gamma irradiation test were carried out. The reflectivity of the H2-free FBG remained stable at ± 120 °C for 100 h or with 50.4 krad γ irradiation, and the central wavelength shifted within 5 pm and 1.6 pm respectively. Regeneration of the fs-FBG was observed in case the FBG was annealed at 800 °C for 5 h, and the remained 5% in reflectivity after 19 h. Such fs-FBGs inscribed in gold-coated fiber could be employed as high performance fiber sensors for space application.
A high resolution and absolute phase interrogation algorithm for Sagnac interferometer based polarization maintaining fiber (PMF) sensor is proposed. Taking wavenumber instead of wavelength as the function variable, the output spectrum will be a standard cosine spectrum function. After Fourier transform, the frequency and relative phase of this spectrum function can be obtained and the precise absolute phase due to optical path difference between the two polarization modes in sensing PMF can be determined. A typical Sagnac interferometer based PMF temperature sensor was built and the absolute phase was determined by use of the proposed algorithm. Experiments show that 0.1°C temperature resolution and up to 900°C temperature can be measured with good linearity.
A gap fiber Bragg grating (g-FBG) is fabricated by cutting a uniform FBG in the middle to introduce a small air gap between the two sections. Numerical and experimental investigations show that the g-FBG has the characteristics of both a phase shifted FBG and a Fizeau interferometer. The influence of the air-gap shift longitudinally or transversely with respect to the fiber central axis and temperature to g-FBG's spectrums are investigated with numerical simulation and experiments, and the mathematic models are made. Based on g-FBG's different sensitivity to gap width and temperature, a micro-gap and temperature simultaneous measurement sensor was demonstrated. And a g-FBG based tunable fiber ring laser with a narrow line-width is demonstrated.
Fiber Bragg gratings (FBGs) in gold-coated SMF have been successfully inscribed with NIR femtosecond laser and a phase mask for high temperature sensing application. The spectrums of FBGs inscribed by femtosecond laser are broader and asymmetrical with flat-toped profile which degrades the accuracy of FBGs interrogation with common peak detection techniques. A smart interrogation algorithm based on pattern matching (PMSIA) is reported in this paper. In this algorithm, an adjustable fitting spectrum template was proposed which enables the ability to suit for various spectrum patterns was proposed. The results of simulation and experiment demonstrate the noise immunity and threshold reliability of PMSIA. Less than 7pm interrogation error PMSIA was obtained even if the spectrum changes greatly in the very large sensing temperature range (up to 700°C).
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.
An intrinsic optical fiber hydrogen sensor based on polarization-maintaining photonic crystal fiber (PM-PCF) Sagnac interferometer was proposed. The facing target sputtering technique with special Pd/Ag plate target structure was developed to deposit Pd/Ag composite film on PM-PCF. The characteristic of Pd/Ag film was measured and analyzed. An experimental setup for hydrogen sensing was built. The wavelength at different hydrogen concentration and the temperature interference were tested. The results showed the sensitivity was higher at low concentration range and good repeatability was obtained within measuring range of 4%. And the temperature affect was weak with special PM-PCF.
A method for building a 1×N fiber coupler based on a single polyhedral gradient-index lens (p-GRIN) is proposed. One end of the p-GRIN has polyhedral convex cone shape with N surfaces and is used as the light input port, while the other end is flat and used as the output port. When light from a single mode optical fiber illuminates the input end of the p- GRIN, N spatially separated light beams are generated at the output end and coupled respectively into N different output fibers. Results obtained from ray-tracing agree well with simulation results from the ZEMAX software. The output beam positions and light coupling efficiency to optical fibers could be optimized by adjusting the input cone angle and the distance between input fiber end and cone tip. This method may be adapted for any type of optical fibers and provide a practical solution for light coupling between single- and multi-core fibers.
We demonstrated an active radiation hardening technology for fiber optic source developed for high performance fiber optic gyroscope. The radiation characteristic of erbium-doped fiber was studied experimentally. The radiation induced attenuation (RIA) at 980nm pump light was identified to be the main reason for the degradation and there was photo-bleaching effect in EDF too. A variable parameters control technology was proposed and taken to keep the 980nm and 1550nm light energy stable and high stability and radiation-resistance fiber source with gauss profile spectrum was realized .The source can stand against more than 50 krad (Si) total radiation dose.
Eigen frequency is a very important parameter in a fiber optic gyroscope (FOG). To establish an accurate measurement of eigen frequency, we propose a new measurement method based on employing the square-wave, over-bias modulation with double eigen frequency. We investigate the proposed method both experimentally and theoretically. Experimental results show the measurement accuracy of eigen frequency is better than ±5 Hz, which satisfies the eigen frequency measurement of most FOGs. A theoretical model of the method gives a good explanation of the experimental results. The method is simple, low-cost, and easy to implement. In addition, it can greatly improve the accuracy of the eigen frequency measurement without needing additional hardware for existing gyro systems.
We characterized the temperature sensitivity of birefringence of typical solid core polarization maintaining photonic
crystal fiber (PM-PCF). Mainly the temperature dependence of birefringence is determined by two factors which are
thermo-optic effects and thermal expansion. Numerical simulation with ANSYS and RSOFT show that the birefringence
temperature susceptibility can be described as a polynomial function of Λ (distance between small holes) and zero
temperature coefficient may be obtained at optimum Λ. A high precision birefringence measure setup was built and the
birefringence of five PM-PCFs samples with different Λ were measured under different temperature. The experimental
result agreed well with the simulation.
An Arc Discharge Erasing (ADE) technique was proposed to erase the refractive index modulation at selective area in
Fiber Bragg Gratings (FBGs) and was taken to fabricate Phase Shift FBGs (PSFBGs). The ADE effect and the PSFBGs
fabrication technology was demonstrated experimentally first. The capability and fabrication technique was investigated and the full control of the transmission spectral characteristics of PSFBGs, including the peak wavelength position, intensity and bandwidth, was demonstrated. To get optimum technique parameters, the experimental studies were done under different discharge electric current, time and position, and the effect of annealing processing were investigated experimentally too. With this technique, an in-line distributed feedback fiber laser with 1.16 kHz line-width was made.
The evolutions of residual pump power and forward Raman Stokes scattering light power with increasing pump
power level are investigated by numerical simulation. The Stokes power variation shows obviously threshold
characteristic which is similar to that of laser diode, and the pump power corresponding to the maximum of the second
derivative of the Raman Stokes signal vs. pump power curve was defined as the pump threshold. A threshold equation
was obtained by fitting the results obtained for different fiber characteristic parameters β. Simple experiments were
carried out with a pulse pump laser and a 24 km long single mode fiber, and the experimental results agree well with the
result obtained threshold equation numerically.
A gap fiber Bragg grating (g-FBG) is fabricated by cutting a uniform FBG in the middle to introduce a small air gap
between the two sections. Numerical and experimental investigations show that the g-FBG has the characteristics of both
a phase shifted FBG and a Fizeau interferometer. The peak transmission wavelength of the g-FBG can be tuned by
adjusting the air-gap longitudinally or transversely with respect to the fiber center-axis. With a g-FBG as tunable
intra-cavity filter, a tunable fiber ring laser with a narrow line-width is demonstrated. The wavelength tuning range of the
laser is 0.12 nm with a output power flatness better than 0.9 dB. The 3 dB spectral line-width is less than 12 pm and
output power is 3.68 dBm.
An embedded pressure sensor was made by sandwiching a polarization maintaining photonic crystal fiber (PM-PCF)
between two polymer foils. The excess birefringence induced by transverse pressure applied along the slow-axis of a
PM-PCF was numerically simulated with a finite element method. Experiment was carried out with a Sagnac
interferometer with the embedded PM-PCF as part of the Sagnac loop. The output interference fringes were found shift
linearly with applied transverse pressure with a wavelength to pressure sensitivity of 1.764 nm/MPa, The measurement
precision of 0.2%, and a dynamic range of 2.5 MPa were achieved.
Polarization maintaining (PM) photonic crystal fiber (PCF) and Er-doped PCF technologies are investigated for
interferometer fiber optic gyroscope (IFOG) applications. A PM-PCF optimized to achieve low-loss and high
polarization extinction splice-joints with conventional PM fiber pigtails of a multifunction integrated optical circuit
(MIOC) was drawn and tested under different temperature conditions. The loss and polarization crosstalk
properties of a fiber coil made from the PM PCF were measured and compared with conventional PM fiber. An
erbium-doped PCF was designed and fabricated, with which a superfluorescent fiber source (SFS) was made and tested.
The results show that an IFOG with the PM-PCF coil and the Er-doped PCF source could achieve better temperature
performance. An experimental PCF-based prototype IFOG was built and tested , and preliminary results was obtained.
KEYWORDS: Calibration, Sensors, Temperature sensors, Polarization maintaining fibers, Polarization, Signal processing, Temperature metrology, Polarizers, System on a chip, Optoelectronics
A reflection type polarization maintaining optical fiber temperature sensor was designed. The operation principle was
introduced and the sensing equation was made. Analysis shows that the propagation loss variety is the main factor which
will let the sensing equation parameters change. Compared the sensing equation and the expanded equation, the
propagation loss coefficient can be separated with the sensor intrinsical parameters and a simple and practical field
calibration method, with which the whole sensing equation parameters can be calibrated when certain temperature at the sensor probe was given, was proposed and the calculation equation was made. An experimental sensor system was built and the calibration experiments were done by change the propagation loss and the date obtained were analyzed and compared with polynomial fitting and model calculating. The result proved the field calibration technology and the sensing temperature precision can be better than ±0.5°C before and after calibration.
The effect of gamma ray radiation on the performance of a compact Er-doped super-fluorescent fiber source was
investigated experimentally. It was found that the output power and spectrum of the source vary significantly with
radiation dosage and probably the induced background loss for the pump would play a significant role in the observed
variations. A double-pass backward source configuration with an output edge filter was implemented experimentally, and
with proper feedback control pump driving circuitry, such a configuration demonstrated good resistance to gamma ray
radiation.
Selective opening and closing of air-holes in photonic crystal fibers (PCFs) are realized by using a femtosecond infrared
laser and a CO2 laser. By heating/tapering the PCFs while pressurizing those opened holes, the birefringent properties of
the PCFs can be modified. High birefringence of 3.6×10-4 and 1.5×10-3 were obtained by post-processing commercial
LMA-10 and HC-1550-02 fibers.
A hollow-core photonic bandgap fiber polarization controller was made by applying
lateral pressures to three segments along the fiber. The applied lateral pressures result in variable
birefringence along the fiber, which modifies the state of the polarization. This approach may be
applicable to a hollow-core photonic bandgap fiber with little or no inherent birefringence.
Two type of output spectrum profile, flat and gauss profile were realized with gain flatten filter and edge filter
respectively. For high performance fiber optic gyroscope application, a vary parameters control technology was taken
and the less than 0.5 ppm/ °C mean wavelength stability and less than 1% output power stability were achieved within
operation temperature -45 °C - +70 °C .To developing radiation-resistance broadband source, the erbium-doped fiber
radiation characteristic was studied experimentally and the super-fluorescent fiber source configuration parameters and
pump laser diode power were optimized. The radiation-resistance super-fluorescent fiber source module was made.
Experimental test shows that two type of SFS, include gauss and flat profile spectrum, can stand against more than
50Krad(Si) radiation dose.
A Fiber Bragg gratings (FBG) Interrogation scheme with scan fiber laser was demonstrated. The ring cavity scan fiber
laser was investigated and the scan fiber laser module was made and test, the 200Hz scan frequency, ~0.02nm line width,
more than 40nm scan range and more than 1 mW output power were obtained. A 12 channels, 20 FBGs per channel FBG
interrogator was made with this laser module and the high speed signal process circuit base on FPGA. The centroid
finding method which has advantage on interrogation speed and accurate was taken for finding the peak of the return
FBG spectrum. The FBG interrogator was test and less than 3pm standard deviation with 200Hz scan frequency were obtained.
The temperature or/and strain measurement accuracy, resolution and response of distributed optical fiber sensors based
on Rayleigh, Raman and Brillouin scattering are mainly limited by their weak signals and low signal-noise ratio (SNR).
To improve the SNR and response characteristic simultaneity, the wavelet transform de-noising technology was
introduced to distributed optical fiber sensor system. The mother wavelet and the processing of thresholds were
optimized in order to get better SNR and minimize the impact to signal response. A Raman scattering distributed optical
fiber sensing experimental system was set and the signal process arithmetic was realized. Experimental tests indicate that
wavelet de-noising method can notably improve SNR and guarantee the spatial resolution simultaneously. Final contrast
tests suggest that not only the temperature resolution was improved by more than 50%, but also the measurement
accuracy and period were improved greatly.
A novel scheme for tunable optical pulse generation based on fiber sagnac loop was proposed and studied. The key
parameters of the optical pulse were analyzed and testified by simulations and experiments. The repetition rate of optical
pulse is twice the frequency of external square wave modulation signal and can be tuned directly by varying modulation
frequency. The maximal peak value can be achieved when the peak-peak value of the square wave modulation signal
was equal to the half-wave voltage of the phase modulator. Experimental results agree well with theoretical predictions
and simulations.
A wavelength division multiplied (WDM) polarization-maintain fiber sensor system for simultaneous temperature
and pressure measurement is proposed. The system comprises a PANDA fiber polarimetric temperature sensor and a
highly birefringent photonic crystal fiber (PCF) polarimetric pressure sensor, which are multiplexed by use of a
WDM beam splitter/combiner and interrogated in wavelength domain by using a combination of a broadband source
and an optical spectrum analyzer. Preliminary experiments demonstrate a temperature sensitivity of about 1.16nm/oC
and a pressure sensitivity of 2.42nm/MPa with respectively 162.7mm of PANDA fiber and 262.8mm of PCF.
A wavelength demodulation detection scheme was proposed based on the polarization mode interference in polarization
maintaining optical fiber (PMF), and the sensing equation was obtained. Compared to the conventional intensity-based
detection technique, this wavelength demodulation technique overcomes the effect of the source power fluctuation and
the variation of optical loss that occurs in the transmission fiber. An experiment system was setup and the relationship
between the frequency of wavelength domain and temperature was obtained within the temperature range -40 °C to 80 °
C. Experimental results agree well with theoretical prediction.
Brillouin distributed optical fiber sensing system based on spontaneous Brillouin scattering frequency shift measurement
may measure temperature in the optical fiber, due to the dependence of spontaneous Brillouin scattering frequency shift
on temperature. In this paper, nonlinear theoretical models of the Brillouin spectrum in the BOTDR temperature sensing
system are analyzed. The model parameters are optimized with Levenberg-Marquardt algorithm. By numerical
calculation, it is indicated that pseudo-Voigt function can approach approximated the Voigt profile well and quickly.
KEYWORDS: Attenuators, Temperature metrology, Control systems, Photodetectors, Prototyping, Optical filters, Optical isolators, Temperature sensors, Data conversion, Semiconductor lasers
The mean-wavelength stability of broadband fiber source is analyzed: The model between the mean-wavelength and the
pump optical power is revealed based on the theoretical and experimental study on the change of mean-wavelength
under different pump optical power. To promote the temperature stability, a mean-wavelength control scheme is
proposed based on the relation of mean-wavelength, pumping current and environment temperature. The output power
was stabilized with a close-loop control technology by taking a adjustable attenuator. Prototype fiber source was made
and tested. The Mean-wavelength stability 0.5×10-6/°C and output power stability 3% within -45°C ~+70°C was
achieved.
A wavelength domain technique based on the detection of peak wavelength in the interference pattern was proposed and
applied to a reflection type polarimetric temperature sensor made of polarization maintaining fibers. The measurement
equation that relates the temperature variation linearly to the shift of the peak wavelength in the interference pattern was
derived. An experimental sensor was setup to verify the effectiveness and the accuracy of the detection technique over
an applied temperature range from -40°C to 80°C. Experimental results agree well with theoretical prediction.
A broadband, compact in-fiber polarizer was fabricated by using a pulsed CO2 laser to modify the air-holes along oneside
of a hollow-core photonic bandgap fiber. The polarizer has a length of 3 to 6mm and exhibits a polarization
extinction ratio of better than 20 dB over a wavelength range of 100nm around 1550nm.
The stability of the mean wavelength of Er-droped superfluorescent fiber sources with a direct sampling control unit,
intended for fiber-optic gyroscope applications, are explored theoretically and experimentally. The mean wavelength
variation versus ambient temperature is measured, and the experimental result shows that the mean wavelength is
correlated to the sampling voltage, which is in good agreement with theoretical analysis. The thermal effects are modeled
to reduce the influence of temperature variation based on the characteristic of monitoring photodiode, and the control
algorithms based on the temperature model are implemented in a standard microprocessor system without additional
hardware. The results show that the temperature stability of the SFS mean wavelength is better than 1ppm/°C over the
entire range of operating temperature, which confirm that this method is effective, and meet the stringent requirements of
the FOG.
The coating resin performance of the Polarization-Maintaining fiber coil is an important fact to affect the performance of
the FOG. It is one of some problems in the fact during the industrialization of the FOG. From the action and effect on the
two important performance parameters such as temperature and vibration of the fiber ring and Fiber Optical Gyroscope
(FOG). In allusion to the factual conditions of the FOG, all aspects of experiments are done and the experiment results
are analyzed. The experiment and analysis results show that the facts to affect coating resin performance of the
Polarization-Maintaining fiber coil is brought due to the unsuitable coating adhesive. The amount and uniformity of
coating resin are the two main facts of the effect. In addition, the temperature performance of the resin and the remaining
stress which are the facts to affect the coating resin performance of the Polarization-Maintaining fiber coil can not be
ignored.
KEYWORDS: Sensors, Temperature sensors, Polarization, Fiber optics sensors, Fiber optics, Digital electronics, Environmental sensing, Signal detection, Temperature metrology, Polarizers
A time-division multi-point precision temperature sensor based polarization mode interference in polarization maintain fiber was
proposed. The sensing principle was demonstrated and a practical mathematical model was obtained. With time division technology,
the digital multi-points temperature sensor system was designed and realized. An experimental system was set with digital circuit
based on micro-processor. The linearity technology and its precision were investigated. With the mathematical model, the linear
output was obtained within -15°C~+55°C and this scheme was proved. The physical 0°C environment was formed with the
mixer of ice and water and one hour sensor output in 0°C environment was recorded. Experimental result shows the resolution and
stability of the temperature sensor can be better than 0.01°C.
Temperature sensing with Sagnac-like fiber interferometer is investigated. Experiments demonstrated very good linearity, repeatability, and a noise-equivalent minimum detectable temperature resolution of better than 0.01°C.
A temperature sensor based on polarization non-reciprocity in fiber Sagnac interferometer was proposed and investigated theoretically and experimentally. Special signal detection schemes were proposed and an experimental system with an all polarization configuration was setup. The temperature measurement experiment was done within -40°C ~ +60 °C range and the stability were investigated at absolute 0 °C in mixture of ice and water respectively. The result agrees with theory well and good performance has been obtained with parameters optimized. Discussion shows that this kind of temperature sensor can achieve high precision and has great application potential.
A double-pass super-fluorescent fiber source with a wavelength-selective reflector fabricated using thin film filter technology was demonstrated. The simulation on output power and bandwidth and meanwavelength were made. The optimized parameters have been obtained and the desired reflector has been fabricated. A practical prototype was made and tested, its output power is great than 8.5 mW, the bandwidth is great than 28nm. The instability of power and meanwavelength are less than 3% and 3ppm/°C within -40 °C ~+60 °C temperature range respectively.
Based on the characteristic of thermal induced nonreciprocity in coil of fiber optic gyroscope (FOG) and the heat-conduction model, a simple and universal model was worked out. It is a low-pass and time delay response to temperature. The model was digitized with a digital smooth filter process and a time delay process and the experimental study was done with an open-loop FOG. The bias drift due to temperature was reduced to 18.2% of that before compensation.
The characteristic of Erbium-doped superfluorescent fiber source was introduced. The double pass backward configuration superfluorescent fiber source was demonstrated mainly and two wavelength selected reflector, thin file filter and fiber bragg grating, were taken to form two superfluorescent fiber source. Their whole parameters, including power, spectrum and spectrum width, were tested, the coherence was calculated and the mean wavelength temperature stability is tested too. The result proved the superfluorescent fiber source with thin film filter and fiber bragg grating are both suitable to inertial grade fiber optic gyroscope.
A mathematic model about split ratio and polarization crosstalk of polarization-maintain fiber couplers have been built and the experimental study has been done. The result showed that the split ratio and polarization crosstalk both varied with the temperature and the variation is linear approximately. The split ratio variation due to the induce light polarization orientation change was measured too. Experimental result were coincident with the theory model exactly.
The temperature characteristic of components used in open-loop fiber-optic gyroscope (FOG) were studied independently and their relevant temperature models of thermal induced error were obtained A digital compensation method, in which a simple phase sensitive detection electric circuit and a microprocessor were adopted and the error compensation was realized with digital processing technology, was proposed. Experimental study showed that the bias drift of FOG tested was reduced abut 80% in the temperature range of 20 degrees Celsius - 55 degrees Celsius after compensation.
A high-precision measure scheme for half-wave voltage V(pi ) of Y-tap MIOC is proposed. This scheme is based on Sagnac interferometer and a saw-tooth wave with special period is used. With this scheme, the temperature characteristics of V(pi ) of a type of MIOC is studied experimentally. The result shows that its half-wave voltage is temperature-dependent. In the range of -10 to +55, the varying value is 0.162V, the temperature coefficient is 662 PPM/degrees C and the variation is linear and repetitive. Experimental study and detail discussion demonstrate that high accuracy can be achieved with this scheme and it is very suitable to be used in studying and calibrating V(pi ) of the modulator used in close-loop FOG in-site.
Basing on the loop characteristic of closed-loop I-FOG, we propose a novel fail self-diagnosing technique and
get a self-diagnosable closed-loop I-FOG. Using this kind of Gyro in redundant Strapdown inertial measure unit
(RSDIMU), we design a simple and effective fault detection. isolation and system reconfiguration(FDIR) algorithm
and calculate its reliability using Markov reliability evaluation mode. Compared with the old system, the reliability
and the fault tolerant capability are all improved greatly.
The mathematical representation of modulation coefficient and intrinsic phase delay of PZT fiber-optic phase modulator are given. To study the temperature character, this paper design two measure system with a Mach-Zehnder and a Sagnac interferometer and get the experimental result curve which show that both parameters are linear with temperature approximately in set temperature range.
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