Compensation of parasitic effects for a silicon tuning fork gyroscope

This paper refers to a silicon micromachined tuning fork gyroscope, which is driven via two piezoelectric thin film actuators. The device responds to an external angular rate by a torsional motion about its sensitive axis due to the Coriolis effect. The shear stress in the upper torsional stem, which is proportional to the angular rate, is detected via a piezoresistive readout structure. In addition to the wanted signal corresponding to the angular rate, there are unwanted contributions from the drive motion, e.g., from mechanical unbalances and from asymmetries of the piezoelectric excitation induced by fabrication tolerances. These effects, which disturb the sensor signal with varying contributions in amplitude and phase, have already been examined for capacitive surface micromachined sensors. In this paper, they are identified for a piezoelectrically driven, bulk-micromachined gyro and compared to results of FEM simulations. System-level simulations are performed and show possibilities to compensate the main parasitic effects. Results of eliminating the mechanical unbalance by femtosecond laser trimming are presented and compared with the simulations.     

Compensation of excess noise in a fiber-optic gyroscope with a 3×3 directional coupler

It is shown theoretically that the excess noise of the radiation source can be compensated in a fiber-optic gyroscope with a 3×3 ring directional coupler and a differential amplifier at the exit. This noise is one of the main factors limiting the precision of a fiber-optic gyroscope. Pis’ma Zh. Tekh. Fiz. 23, 36–38 (August 12, 1997)     

Phase modulation spectroscopy using an all-fiber piezoelectric transducer modulator for a resonator fiber-optic gyroscope

The theoretical analysis and experimental demonstration of phase modulation spectroscopy employing an all-fiber piezoelectric transducer modulator for a fiber ring resonator fiber-optic gyroscope is presented for the first time as far as we know. The results support the feasibility of such a technique as a rotation detection scheme for a resonator fiber-optic gyroscope.     

使用光纤陀螺进行精确测量的矢量调制法

以光纤陀螺工程测量为例,提出了精确测量矢性物理量的矢量调制法。依据调制解调原理和线性系统理论,矢量调制法使用机械转动方法,将输入信号在进入传感器之前调制成为正弦波;由于线性传感器的频率保持性和叠加特性,对传感器输出信号解调,将得到准确的输入响应,由此去除常见的传感器偏置、偏置的漂移、干扰与噪声。与其它抑制测量误差的方法(最优估计、滤波等)相比,提高测量精度效果更明显。初步实验表明,使用低精度光纤陀螺能够测量地球自转角速率,能够从 mV 级直流量、峰峰值(-18mV, 1mV)的噪声和干扰中分离出北向地速响应,与北向地速响应的计算值 0.03mV 接近。     

Effective fiber-optic polarization modulator

A fiber-optic polarization modulator based on a piezoelectric ceramic transducer is considered. The device employs the phenomenon of photoelasticity, whereby the polarization of light in the fiber is modulated due to the birefringence variations induced by oscillating transverse pressure applied to the fiber. An analytical expression for the modulation efficiency is obtained. A high efficiency of the proposed modulator is confirmed by experimental data.     

Digital signal processing for an open-loop fiber-optic gyroscope

Open-loop fiber-optic gyroscopes (FOG's) are generally less stable than closed-loop FOG's, yet they offer simpler implementation. We propose a modification of the harmonic division algorithm for an open-loop FOG, which is more stable and also simpler for implementation than the original one. It is shown that when the analog signal is properly sampled and quantized, the performance of our algorithm reaches that of closed-loop FOG's. Our algorithm may be implemented by the use of off-the-shelf component, and does not require an integrated optics circuit.     

New interferometric fiber-optic gyroscope with amplified optical feedback

A novel interferometric fiber-optic gyroscope with amplified optical feedback by an Er-doped fiber amplifier (EDFA) is proposed and theoretically investigated (the proposed gyroscope is named the feedback EDFA-FOG, FE-FOG in what follows). The FE-FOG functions like a resonant fiber-optic gyro (R-FOG) because of its multiple utilization of the Sagnac loop; however, it is completely different because a low-coherence light source is used. In addition, the gyro output signal is pulsed because the modulation frequency of the phase modulator placed in the Sagnac loop is selected to match the total round-trip time delay of the light, which includes the Sagnac-loop delay plus that of the feedback loop of the fiber amplifier. The sharpness of the output pulse can be adjusted by both the gain of an EDFA and the modulation depth of the phase modulator. When rotation occurs the peak position of the output pulse is shifted as a result of the Sagnac effect. The resolution of the rotation measurement depends on the sharpness of the output pulse. The techniques of both the open-loop and closed-loop methods are described in detail, which shows the great advantage of the proposed gyroscope over the to the conventional interferometric fiber-optical gyroscope (I-FOG).     

Analysis of polarization properties of a mode-locked fiber laser gyroscope

We investigated the polarization characteristics of a mode-locked fiber laser gyroscope (MLPLG) formed with a Nd-doped fiber as an optical gain medium and a Sagnac loop mirror. The output pulse patterns and the polarization states were found to be determined by fiber birefringence in the different sections of the MLPLG. We describe the conditions for the MLPLG to operate with automatic reciprocity leading to the possibility of phase-error-free operation.     

Inline fiber-optic polarization analyzers for sensor application

Theoretical and experimental investigations of a new type of inline fiber-optic polarization analyzer are described in this paper. The discussed devices are based on a polarimeter, as well as a Sagnac interferometer configuration, and give the possibility to detect the full polarization changes. Detection of the polarization state as well as its degree in real time by the systems containing a standard single-mode fiber and application of appropriate modulation technique is a new property of the arrangement. The comparison of the described systems based on experimental device investigation is also presented in this paper.     

Two mechanisms of phase modulation in multimode fiber-optic interferometers

The mechanisms of phase modulation of optical radiation in multimode light guides are treated, namely, the first mechanism with equal relative phase increments for all modes and the second mechanism including the mode interaction and characterized by different relative phase increments for each mode. It is demonstrated theoretically that, in the case of several modulating effects on the light guide, the behavior of signals of modal interference from each one of those effects upon variation of the parameters of the medium surrounding the fiber depends on the type of effect. The variations of signals from the effects of the first type are in full agreement. Signals from effects of the second type or of different types may vary differently. In experiments with an intermode fiber-optic interferometer 500 m long, modulators associated with the mechanism of the first type exhibited a high correlation (97%) of the behavior of signals upon drift of the light guide temperature. The variations of signals from modulators of the second type and of different types were almost uncorrelated (6 and 1%).     

Analysis and modeling for fiber-optic gyroscope scale factor based on environment temperature

To explore and reduce the nonlinear error and temperature dependency of fiber-optic gyroscope (FOG) scale factor, a scale factor modeling method based on temperature is presented in this paper. A hyperbolic curve fitting is proposed according to the characteristic of scale factor under stable temperature at first. Compared to traditional modeling methods, it shows that a higher precision model of scale factor can be obtained. Then the influence of temperature on scale factor is analyzed and then the hyperbolic curve fitting method is extended based on temperature, making it possible to work over the whole potential temperature range of the FOG without degrading the performance. This paper also provides the experimental and verification results. It can be seen that a high precision model of scale factor has been established, the temperature dependency of scale factor has been reduced effectively, and the error due to environment temperature is reduced by one order at least.     

伪随机调制在全数字闭环光纤陀螺中的应用

伪随机调制信号的抗干扰能力强,获得同样的信号,对系统正常运行的干扰程度比其他测试信号低。光纤陀螺的输出信号微弱,背景噪声强,在频域随机分布,增加了信号处理的难度。结合伪随机调制的优势,在原有的数字闭环信号处理的基础上,提出了一种新的信号处理方案:伪随机调制解调方案,与数字闭环方案相互配合,有效提取环境因变量,反馈至系统使之实时做出补偿,提高陀螺稳定性。     

Orthogonal polarization fiber gyroscope with increased stability and resolution

The orthogonal polarization fiber gyroscope (OPFG) is an interferometric fiber gyroscope design that requires no phase bias in the fiber ring and is insensitive to light-source intensity noise. However, in the original OPFG [Hitachi Rev. 33, 215 (1984)], environmental changes caused first-order false rotation signals. We propose and experimentally verify modifications that eliminate the first-order sensitivity to environmental changes and that improve the gyroscope's resolution as well. We believe that this modified OPFG is the first interferometric fiber gyroscope capable of stable, high-sensitivity measurement that contains only reciprocal optical elements.     

Investigation of polarization-induced fading in fiber-optic interferometers with polarizer-based polarization diversity receivers

A technique is described to eliminate polarization-induced fading in fiber-optic interferometers with two or three polarizers. Modeling and simulation show that two polarizers should be angularly spaced by 90 degrees to alleviate polarization-induced fading. A test system is set up with two 6.5 km fiber coils to link the data. A bistate polarization diversity receiver is tested for reducing polarization-induced fading. The signal is demodulated using a digital phase-generated carrier and the system demonstrates self-noise up to 7.7 microrad/square root Hz (at 1 kHz).     

Cross-phase modulation in polarization shift-keying lightwave systems

We investigate the effect of cross-phase modulation in wavelength-division-multiplexed polarization-modulation lightwave systems. Analytical expression for the Q factor penalty in terms of signal power, the number of channels, and other parameters are derived. The theory is compared with numerical experiments.     

Open-loop operation experiments in a resonator fiber-optic gyro using the phase modulation spectroscopy technique

A detection system in the resonator fiber-optic gyro is set up by the phase modulation (PM) spectroscopy technique. The slope of the demodulated curve near the resonant point is found to affect the ultimate sensitivity of the gyro. To maximize the demodulated signal slope, the modulation frequency and index are optimized by the expansion of the Bessel function and optical field overlapping method. Using different PM frequencies for the light waves, the open-loop gyro output signal is observed. The modulation frequency in this PM technique is limited only by the cutoff frequency of the LiNbO3 phase modulators, which can reach several gigahertz. This detection technique and system can be applied to the resonator micro-optic gyro with a less than 10 cm long integrated optical ring.     

Performance analysis of a time-division-multiplexed fiber-optic gas-sensor array by wavelength modulation of a distributed-feedback laser

The results of an investigation of the performance of a time-division-addressed fiber-optic gas-sensor array by means of wavelength modulation of a distributed-feedback (DFB) laser are reported. The system performance is found to be severely limited by the extinction ratio of the optical switch used for pulse amplitude modulation. Formulas that relate the cross-talk level to the extinction ratio of the switch, the modulation parameters of the DFB laser, and the optical path differences among sensing channels are derived. Computer simulation shows that an array of 20 methane gas sensors with a detection sensitivity of 2000 parts in 10(6) (ppm) (10-cm gas cell) for each sensor may be realized with a commercially available single Mach-Zehnder amplitude modulator (-35-dB extinction ratio). An array of 100 sensors with a 100-ppm detection sensitivity for each sensor may be realized if a double Mach-Zehnder amplitude modulator is used.     

High-rate-long-distance fiber-optic communication based on advanced modulation techniques.

The presence of fiber attenuation and chromatic dispersion is one of the major design aspects of fiber-optic communication systems when one addresses high-rate and long-distance digital data transmission. Conventional digital communication systems implement a modulation technique that generates light pulses at the fiber input end and tries to detect them at the fiber output end. Here an advanced modulation transmission system is developed based on knowledge of the exact dispersion parameters of the fiber and the principles of space-time mathematical analogy. The information encodes the phase of the input light beam (a continuous laser beam). This phase is designed such that, when the signal is transmitted through a fiber with a given chromatic dispersion, high peak pulses emerge at the output, which follows a desired bit pattern. Thus the continuous input energy is concentrated into short time intervals in which the information needs to be represented at the output. The proposed method provides a high rate-distance product even for fibers with high dispersion parameters, high power at the output, and also unique protection properties. Theoretical analysis of the proposed method, computer simulations, and some design aspects are given.     

Standard apparatus for measuring polarization mode dispersion in fiber-optic data transmission systems

Methods and instruments for ensuring the uniformity of polarization mode dispersion measurements in fiber-optic data transmission systems are described. The results of the development of a standard measuring instrument and working standards of the unit of dispersion are presented. The results of metrological investigations of a standard measuring instrument are also given.