T型反馈网络在谐振式光纤陀螺频率锁定中的应用

谐振式光纤陀螺（R-FOG）的频率锁定是陀螺信号检测的关键技术,尤其在长时间的测试中,谐振频率的锁定稳定度决定了陀螺的输出性能。根据光纤环形谐振腔的传输理论,分析了其谐振特性及其一次谐波特性;搭建了R-FOG测试系统,采用正弦波相位调制解调技术实现谐振谱线一次谐波的输出;在分析由运算放大器构成的传统模拟比例积分（PI）电路的漂移误差源的基础上,给出了可以有效抑制漂移误差的T型反馈网络,应用到谐振式光纤陀螺的谐振频率锁定中,得到了较好的锁定效果,经Allan方差分析,谐振频率长时间（4000s）的锁定稳定度优于910-12。     

A single-mode optical fiber ring resonator using a planar 3×3fiber coupler and a Sagnac loop

We present the first theoretical analysis of an optical fiber ring resonator using a planar 3×3 fiber directional coupler and a fiber Sagnac loop. In the planar 3×3 fiber directional coupler, the three fibers inside the coupler lie in the same plane. Expressions for the circulating (resonant) and the output fields of the fiber ring resonator are obtained. It is found that this fiber ring resonator has a special property where there are two or more main resonance peaks or dips inside a period 2π of the phase change of the fiber ring resonator. This ring resonator may have applications as a sensor with high-phase sensitivity and a densely spaced two-channel wavelength division multi/demultiplexer     

Reduced thermal sensitivity of hybrid air-core photonic band-gap fiber ring resonator

A novel hybrid air-core photonic band-gap fiber (PBF) ring resonator with twin 90° polarization-axis rotated splices is proposed and demonstrated. Frist, we measure the temperature dependent birefringence coefficient of air-core PBF and Panda fiber. Experimental results show that the relative temperature dependent birefringence coefficient of air-core PBF is 1.42×10-8/°C, which is typically ~16 times less than that of Panda fiber. Then, we extract the geometry profile of air-core PBF from scanning electron microscope (SEM) images. Numerical modal is built to distinguish the fast axis and slow axis in the fiber. By precisely setting the length difference in air-core PBF and Panda fiber between two 90° polarization-axis rotated splicing points, the hybrid air-core PBF ring resonator is constructed, and the finesse of the resonator is 8.4. Environmental birefringence variation induced by temperature change can be well compensated, and experimental results show an 18-fold reduction in thermal sensitivity, compared with resonator with twin 0° polarization-axis rotated splices.     

光纤环形谐振腔输入功率波动对谐振式光纤陀螺的影响

谐振式光纤陀螺是一种基于Sagnac效应的高精度惯性传感器。作为一种互异性噪声,光纤谐振腔输入功率的波动会造成陀螺的检测误差。首先,分析了光纤谐振腔输入功率波动产生噪声的机理。通过对不同输入功率下的谐振腔传输特性和陀螺解调输出的理论及实验分析得到了谐振腔输入功率波动引起的检测误差的表达式。当输入角速度为500（）/s、输入功率为0.69 mW时,0.007 5 mW的功率波动会引起5.26（）/s的检测误差。其次,研究了谐振腔输入功率波动对陀螺标度因数的影响。通过计算发现随着输入功率波动的增大,解调曲线的线性区将会发生扭曲,同时陀螺的标度因数非线性度会恶化,为谐振式光纤陀螺中输入功率波动噪声的估测提供了参考。     

Bias of a resonator fiber optic gyro composed of apolarization-maintaining fiber ring resonator with the photoinducedbirefringent grating

A theoretical study of the polarization-fluctuation induced bias of an resonator fiber optic gyro (R-FOG), which employs a polarization-maintaining fiber ring resonator with a photoinduced birefringent grating, is presented. The polarization conversion due to the photoinduced birefringent grating can stabilize the resonator output, which result in the reduction of the bias in the R-FOG output. The influences of the parameters, such as the fluctuation of the input polarization, the resonator finesse, and the photoinduced index change of the dielectric tensor, on the bias in the gyro-output have been investigated. Our results show that with the help of a photoinduced birefringent grating the bias in the gyro-output can be limited around 10^-7 rad/s (0.02 deg/hr), a typical specification for the aircraft-navigation     

谐振式光纤陀螺的研究进展

谐振式光纤陀螺作为新一代惯性旋转传感器的代表，被广泛研究．文章通过大量的文献调查和深入研究，对谐振式光纤陀螺的发展历史、基本工作原理、主要噪声因素及相应的补偿措施等进行了详细分析，并对谐振式光纤陀螺未来的发展趋势作了展望．     

CORDIC algorithm based digital detection technique applied in resonator fiber optic gyroscope

A digital detection technique based on the coordinate rotation digital computer (CORDIC) algorithm is proposed for a resonator fiber optic gyroscope (R-FOG). It makes the generation of modulation signal, synchronous demodulation and signal processing in R-FOG to be realized in a single field programmable gate array (FPGA). The frequency synthesis and synchronous detection techniques based on the CORDIC algorithm have been analyzed and designed firstly. The experimental results indicate that the precision of the detection circuit satisfies the requirements for the closed-loop feedback in R-FOG system. The frequency of the laser is locked to the resonance frequency of the fiber ring resonator stably and the open-loop gyro output signal is observed successfully. The dynamic range and the bias drift of the R-FOG are ±1.91 rad/s and 0.005 rad/s over 10 s, respectively.     

Performance parameters of a wavelength-division demultiplexer madewith a single 3×3 coupler optical fiber ring or loopresonator

The performance parameters of a two-channel demultiplexer made with a single 3×3 coupler fiber ring or loop resonator are evaluated theoretically. These parameters include crosstalk, output intensity of the selected channel, and channel separation. Their dependence on the parameters of the coupler and the fiber such as the coupling length of the coupler, kd, the phase change of the fiber delay line, &thetas;, and the round-trip amplitude transmission coefficient of the fiber ring or loop G, which is the product of the amplitude transmission coefficients of the coupler and the fiber delay line and the amplitude gain of the degenerate two-wave mixing, is investigated. It is found that the best performance can be obtained at G=1     

Analysis of four-port optical fiber ring and loop resonators usinga 3×3 fiber coupler and degenerate two-wave mixing

A theoretical analysis of four-port optical fiber ring and loop resonators using a 3×3 fiber directional coupler and degenerate two-wave mixing is presented. Expressions for the circulating (resonant) and output fields and intensities, as well as resonance conditions for two slightly different configurations of the loop resonator and for the ring resonator are obtained. It is found that the use of the degenerate two-wave mixing greatly improves the characteristics of these resonators. For example, the crosstalk of the ring or loop resonators when used as a wavelength division demultiplexer can be significantly deduced     

Analysis of fiber Brillouin ring laser composed ofsingle-polarization single-mode fiber

A fiber Brillouin ring laser made of SPSM fiber is analyzed. The eigenstate of polarization (ESOP) is strictly considered both for the pump and the Stokes light. It is clarified that the laser intensity fluctuation caused by the interaction between two kinds of ESOP is highly suppressed in this structure. The numerical computations using the typical values show that the fluctuation within 7.5% can be realized for the output Stokes light. While this ring-resonator does not offer high-grade performance when applied to the passive resonator fiber optic gyro, it could realize the high-grade performance when applied to the Brillouin fiber optic gyro     

Dynamic behavior of reflection optical bistability in a nonlinearfiber ring resonator

We present an analysis of the dynamic behavior of a nonlinear fiber ring resonator when an optical pulse with an arbitrary shape envelope is incident into it through a fiber directional coupler. The transient analysis is based on the extension of a well-known multiple-beam interference method to non-linear transmission problems. The steady-state analyses reported so far predict that the ring resonator exhibits reflection optical bistability in the input-output characteristics under appropriate conditions. But, our transient analysis shows that a nearly periodical oscillation of the transmitted power always takes place at a suitable initial detuning when the resonator has no loss or a small loss. It seems that the present instability is caused by the repetition of accumulation and release of the power in the ring resonator. We can obtain a bistable hysteresis loop by introducing a loss to the directional coupler. The dynamic behavior of bistability in a nonlinear fiber ring resonator with coupler loss is then investigated. It is found that a remarkable undershoot and overshoot occur in the switch-off curve and switch-on curve, respectively     

两光纤激光器同相锁定的实验研究

基于自成像共焦腔,利用一个设计灵活的实验装置,实现了两路掺镱光纤激光器的同相模式锁定。改变近场填充因子为10.86%,15.2%,25.33%时,干涉条纹旁瓣数量逐渐减少,主瓣能量占总能量比例分别为13.58%,18.98%,31.42%。在8.8 W泵浦功率下得到1.44 W相干合成激光输出,相干合成效率93.4%。研究发现选用合适长度的增益光纤和较小反射率的外腔输出耦合镜可以提高激光斜效率,进而增加相干合成输出功率。     

An optimal open-loop multimode fiber gyroscope for rate-grade performance applications

We report the realization of a new version of a fiber optic gyroscope (FOG), using low-cost multimode fiber components. This is achieved by an optimal choice of the components such as fiber, coupler, light source and photodetector. The aim behind this work is to demonstrate the versatility of the low-cost multimode FOG for rate-grade performance applications. Both analog signal processing and open-loop operation are used in the proposed FOG experiment. The obtained sensitivity is ∼7°/h and the angle random walk is about 0.087°/. The influence of the coupler technology on the performances is investigated.     

An Open-Loop Test of a Resonator Fiber Optic Gyro

谐振式光纤陀螺是基于光学Sagnac效应来测量载体旋转角速度的一种新型传感器.利用调相谱检测技术,建立了谐振式陀螺的开环响应测试系统.利用自行研制的锁相放大器和反馈控制电路,得到了线性度很好的解调曲线.从解调曲线的线性工作区可进一步得到系统的动态范围高达 4.2～-4.2rad/s.通过对顺时针和逆时针光路采用不同的频率调制,成功地观察到对应两个不同旋转方向的陀螺开环响应输出信号.最后,对系统的零漂进行了测试,在5s时间内观察到系统的零漂为0.02rad/s.     

谐振式光纤陀螺开环响应测试

谐振式光纤陀螺是基于光学Sagnac效应来测量载体旋转角速度的一种新型传感器.利用调相谱检测技术,建立了谐振式陀螺的开环响应测试系统.利用自行研制的锁相放大器和反馈控制电路,得到了线性度很好的解调曲线.从解调曲线的线性工作区可进一步得到系统的动态范围高达+4.2～-4.2rad/s.通过对顺时针和逆时针光路采用不同的频率调制,成功地观察到对应两个不同旋转方向的陀螺开环响应输出信号.最后,对系统的零漂进行了测试,在5s时间内观察到系统的零漂为0.02rad/s.     

二氧化硅光波导环形谐振腔

利用宽角光束传输法(WA-BPM)对二氧化硅平面波导环形谐振腔进行了优化设计,详细分析了不同环形腔长度下,谐振腔清晰度与环形腔耦合器耦合系数的关系,并进一步分析了由光探测器散弹噪声所限制的谐振型光学陀螺极限灵敏度和环形腔光路参量之间的关系。在此基础上,在硅衬底上利用火焰水解化学掺GeO2的二氧化硅波导上制作成带输入/输出耦合器的环形谐振腔芯片。并通过实验测试了所研制的光波导环形谐振腔,其清晰度高达60,理论分析表明采用上述环形谐振腔研制的陀螺,其极限灵敏度可达1°/h。     

Analysis of a fiber-optic passive loop-resonator gyroscope: Dependence on resonator parameters and light-source coherence

Analysis has been made of a fiber-optic passive loop resonator, the heart of the gyroscope. The performance characteristics are heavily dependent on the resonator parameters, such as coupling intensity loss of the input light, coupling coefficient between two fiber lines in an evanescent-field directional coupler, and losses of the light traveling in the fiber loop, as well as on the temporal coherence of the input light. A two input and two output system is considered for a passive loop-resonator gyroscope. Differential output operation of the two output signals is described.     

Experimental optimization of an erbium-doped super-fluorescent fiber source for fiber optic gyroscopes

Double-pass forward and double-pass backward erbium-doped super-fluorescent fiber sources(EDSFSs) were combined in one configuration.A 980 nm laser diode pumped the same erbium-doped fiber from both directions using a coupler as a power splitter.The double-pass configuration was achieved by coating the fiber end face.Firstly,an optimal fiber length was found to obtain a high stability of output light wavelength with pump power, and then 1530/1550 nm wavelength division multiplexing was used for spectrum planarization,which expanded the bandwidth to more than 22 nm.The final step was a test of temperature stability.The results show that the rate of the central wavelength change kept to below 3.5 ppm/℃in the range of -40 to 60℃and 1-2 ppm/℃in the range of 20-30℃.Considering all the three factors of the fiber optic gyro applications,we selected 80 mA as the pump current,in which case the central wavelength temperature instability was calculated as 2.70 ppm/℃, 3 dB bandwidth 22.85 nm,spectral flatness 0.2 dB,output power 5.17 mW and power efficiency up to 9.92%.This experimental result has a significant reference value to the selection of devices and proper design of ED-SFSs for the application of high-precision fiber optic gyroscopes.     

数字调制谐振式光纤陀螺中阶梯波复位误差的分析

谐振式光纤陀螺(R-FOG)是采用环形谐振腔来增强Sagnac效应的，其检测方案可以分为开环和闭环，在电路实现上，根据相位调制器控制信号的不同，又分为模拟调制和数字调制。相比而言，其数字闭环检测方案具有动态范围大、灵敏度高的特点。在数字调制的谐振式光纤陀螺中，其阶梯波的复位高度V2π是否精确，会对旋转角速度的测量和标度因数的线性度产生影响。从理论上分析了不精确的复位高度V2π对系统的影响，指出不精确的V2π将使谐振腔中的交叉耦合电场和直通耦合电场之间不会形成最佳相消干涉，从而产生误差。利用探测器输出总电场的表达式，以双频率调制的谐振式光纤陀螺为例，对引入的误差作了定量的数值计算，最后给出了克服误差的几种方法。     

Receiver analysis for synchronous coherent optical fiber transmission systems

A receiver sensitivity expression applicable for both PSK homodyne and heterodyne optical fiber transmission systems is derived taking account of polarization misalignment, reduced modulation depth, preamplifier thermal noise, power coupling ratio of the fiber coupler, local oscillator excess intensity noise, and reference phase errors. From a comparison of recent studies on system performance degradation due to laser phase noise a generalized expression relating beat linewidth to phase error variance for pilot carrier and Costas phase-locked-loop receivers is defined.