Huilan Liu

Suppression of backreflection noise in a resonator integrated optic gyro by hybrid phase-modulation technology

A method to suppress backreflection noise due to facet reflection in a resonator integrated optic gyro (RIOG) is demonstrated using hybrid phase-modulation technology (HPMT). First, calculations are carried out to evaluate the effect of the backreflection. Although its amplitude has been remarkably decreased by angle polishing, residual backreflection noise is still a severe factor in RIOGs. Next, a hybrid phase-modulation method to eliminate the backreflection noise is constructed, and the frequency spectra of the photodetector outputs before and after adopting HPMT are analyzed. Theoretical analysis shows that the backreflection noise spectra will split from each other as a result of the hybrid phase modulation. In association with the pectinate-filter characteristics of digital correlation detection, the backreflection noise can be suppressed. Finally, the RIOG experimental setup is established and compared with opposite-slope triangle phase-modulation technology. HPMT has the advantage of suppressing backreflection noise, with the RIOG bias stability greatly improved from 2.34 to 0.22 deg/s (10 s integration time).

Current modulation technique used in resonator micro-optic gyro

Resonator micro-optic gyro (RMOG) is a promising candidate for the next generation inertial rotation sensor based on the Sagnac effect. A current modulation technique used in an external cavity laser diode is proposed to construct the gyroscope system for the first time. The resonance curves before and after eliminating accompanying amplitude modulation are theoretically analyzed, calculated, and simulated; the demodulation curves with different modulation currents are formulated theoretically; and the optimum modulation current corresponding to the maximum sensitivity is obtained. The experiment results from the established RMOG experimental setup demonstrate that a bias stability of 2.7 deg/s (10 s integrated time) over 600 s, and dynamic range of ±500 deg/s are demonstrated in an RMOG with a silica optical waveguide ring resonator having a ring length of 12.8 cm.

Effect of intensity variation of laser in resonator integrated optic gyro

The performance of the resonator integrated optic gyro (RIOG) is inevitably influenced by the intensity variation of the laser. In this work, the effect of intensity variation of the laser is mathematically formulized, analyzed, and experimentally validated, to our knowledge for the first time. First, the demodulated curves with different light intensities input of the integrated optical resonator (IOR) are simulated; the relationship between the slope of the demodulated curve near the resonant point and the light intensity input of the IOR is obtained. Second, the amplitudes of the output square waveforms with different zero biases are demonstrated, and it can be concluded that the effect of intensity variation has a high correlation with the nonzero bias between the clockwise and counterclockwise resonant frequency. Third, the experimental setup is constructed and the related measurements are performed, the test results are in good agreement with the analytical and numerical simulation, and in order to reach the limited ultimate sensitivity of the RIOG, it is necessary to restrict the nonreciprocal zero bias within 8.1 deg/s under an open-loop output scheme. Furthermore, to eliminate the noise induced by intensity variation of the laser and realize a high performance RIOG, a closed-loop operation is required.

Reduction of backreflection noise in resonator micro-optic gyro by integer period sampling

In resonator micro-optic gyros (RMOGs), the interference between the backreflection light beam of one pathway and the signal light beam of the other pathway deteriorates the gyro output waveforms, resulting in severe reduction in the gyros accuracy. In this paper, an integer period sampling (IPS) method is introduced to minimize the sampling error caused by backreflection in RMOG for the first time to our knowledge. The experimental results show that both the bias repeatability and the short-term bias stability become better when the IPS condition is satisfied. A bias stability of 0.41°/s over one hour with an integration time of 10 s has been realized in a RMOG that employs a silica waveguide ring resonator.

In-line polarizer used in all-0°-splice resonator fiber-optic gyro

A method to suppress the polarization-fluctuation-induced drift in a resonator fiber-optic gyro is proposed in this paper. By inserting one in-line polarizer whose polarization extinction ratio is 30 dB into a polarization-maintaining fiber resonator with 0° polarization-axis splices, the unwanted resonance is introduced to high loss and therefore the ratio of the resonance height of the desired eigen-states of polarization (ESOP) to the unwanted ESOP is 74 dB theoretically; thus the polarization-fluctuation-induced drift is adequately suppressed. The new scheme has excellent operability and high temperature stability simultaneously. Compared to the resonator with twin 90° polarization-axis rotated splices, this scheme does not need precise length difference control. This work is of great importance in the research on resonator integrated optic gyros.

Design on waveguides coupler for integrated fiber optical gyroscope based on SOI wafer

The application of SOI wafer in integrated optical components provides a novel method of increasing the density of integration, as well as reducing unit cost. This paper designed a new kind of waveguides coupler for an integrated optical transceiver unit of an interferometric fiber optic gyroscope system. Based on effective index method and beam propagation method (BPM), mathematic model of the waveguides coupler was founded, and theory calculation and analysis were finished for key parameters, such as coupling ratio, effective coupling length, division radio and returning loss, etc. Also these parameters were optimized in practice coupler design which used in integrated optical transceiver. The design results indicated that its division radio is 50%:50%, coupler core size is 6μm×5.5μm, length of the chip is 25mm and width between two export ports of the waveguides is 400μm. With electron beam lithography machine the mask of silicon-on-insulator (SOI) waveguides coupler was fabricated. The mask fabrication parameters were developed and optimized in this paper. Detect results shown that this optical waveguides coupler can be used in integrated optical transceiver unit for the interferometric fiber optic gyroscope system. This result can provide significant theory basic for research on high integrated, high reliably, low cost integrated optical components used for interferometric fiber optic gyroscope.

Closed-loop experiment of resonator integrated optic gyro with triangular wave phase modulation

A closed-loop resonator integrated optic gyro (RIOG) scheme based on triangular wave phase modulation is proposed. Only one integrated optic modulator (IOM) is employed. Triangular wave is applied on the IOM to modulate the passing light wave, and the feedback serrodyne wave is superimposed upon the triangular wave to compensate the resonant frequency-difference. The experimental setup is established and the related measurements are performed. The results show that the proposed scheme can realize the closed-loop RIOG employing an IOM, which has the advantage of miniature size. A bias stability of 0.39 deg/s (10 s integration time) over 1 hour is achieved. Moreover, good linearity and large dynamic range are also experimental demonstrated.

Research on a novel MOEMS interferometric gyroscope

MOEMS (Micro-Opto-Electro-Mechanical System) gyroscope is one of the research hotspot of international inertial domain. It combines advantages of optical detect principle of optical gyroscopes and MEMS (Micro-Electro-Mechanical System) fabrication technique. It is solid-state. It has little volume, light weight, good stability, and large dynamic scale. And it can be batch fabricated. These make it has large applications in inertial technology domain. A MOEMS interferometric gyroscope which uses spatial optical paths to sensitive Sagnac effect is presented. A spatial helical optical structure composed of micromirrors was designed. Light traveled in free space, which could reduce wastage. The gyroscope has no coupling problem, no back scatter, and no movable parts. The structure of the gyroscope has advantages in microminiaturization. It could be manufactured using MEMS technics. Theoretical analyses were made to parameters of the spatial optical path from the viewpoint of improving the fundamental detection limit. Theorem proving experiment was researched. Based on experiment design, output signals of the gyroscope on rotate platform were measured using Lock-in amplifier and other instruments. Theorem proving of the Sagnac effect is realized, and the bias stability of the gyroscope system is about 8 °/h.