Jianjie Zhang

Resonant micro-optic gyro using a short and high-finesse fiber ring resonator

A novel hybrid integrated scheme is proposed for a high-performance resonant micro-optic gyro (RMOG), which requires a low-loss micro-ring resonator for mass production. A new record for the RMOG is established experimentally with a short fiber ring resonator and an integrated signal detecting and processing circuit. The finesse of the short fiber ring resonator with a length of 60 cm and a diameter of 4.77 cm is as high as 202, and the theoretical sensitivity of the RMOG is better than 0.3°/h assuming the average optical intensity at the photodetector is 1 mW. The 60 cm long spliceless micro-ring resonator is experimentally proved to be sufficient for a tactical-grade RMOG. An angle random walk coefficient of 0.64°/√h and a typical bias stability below 9.6°/h for the integration time of 50 s are successfully demonstrated using an innovative open-loop approach for an operation time of 1600 s.

Double closed-loop resonant micro optic gyro using hybrid digital phase modulation.

It is well-known that the closed-loop operation in optical gyros offers wider dynamic range and better linearity. By adding a stair-like digital serrodyne wave to a phase modulator can be used as a frequency shifter. The width of one stair in this stair-like digital serrodyne wave should be set equal to the optical transmission time in the resonator, which is relaxed in the hybrid digital phase modulation (HDPM) scheme. The physical mechanism for this relaxation is firstly indicated in this paper. Detailed theoretical and experimental investigations are presented for the HDPM. Simulation and experimental results show that the width of one stair is not restricted by the optical transmission time, however, it should be optimized according to the rise time of the output of the digital-to-analogue converter. Based on the optimum parameters of the HDPM, a bias stability of 0.05°/s for the integration time of 400 seconds in 1 h has been carried out in an RMOG with a waveguide ring resonator with a length of 7.9 cm and a diameter of 2.5 cm.

Development and Evaluation of Optical Passive Resonant Gyroscopes

In this paper, the development and evaluation of passive optical ring resonator gyroscopes (OPRGs) are critical reviewed. Attention has been paid to the countermeasures against the parasitic noise sources which are encountered in the OPRG including backscattering, backreflection, polarization error, nonlinear Kerr effect, and laser frequency noise. The new progress in a feasible OPRG is shown. In addition, the advanced and complex digital signal processing in the OPRGs is also addressed.

Tilted Waveguide Gratings and Implications for Optical Waveguide-Ring Resonator

In this paper, a novel optical waveguide-type ring resonator by inserting titled waveguide gratings (TWGs) with the Brewsters angle is proposed. Using the Marcatili approximation, the electric fields for a rectangular waveguide is obtained. Then, the volume current method (VCM) is first developed for rectangular-core TWGs. By the VCM, the feasibility of the TWGs to filter the s-polarized light propagating in the resonator is proved. When a 4-cm-long 45°-titled TWG is applied to a silica waveguide-ring resonator, a polarization extinction ratio of 40 dB is obtained. The influences of the angular misalignment as well as the grating period of the TWGs are also evaluated.

Resonant micro optic gyro using tens of centimeters long optical fiber coil

A resonant micro optic gyro (RMOG) is a promising candidate for applications requiring small, light and robust gyros. A high-performance RMOG requires a low-loss micro-ring resonator, and thus a resonator having a high finesse. We experimentally create a new record for high-finesse micro-ring resonators by using 30-cm long low-loss fiber coils laid into the V-groove on a silicon substrate. Both the simulation and experimental results indicate that the 30-cm long micro-ring resonator is sufficient to build a tactical-grade RMOG. Experimentally, a bias stability of 0.046/s in 1800 s with an integration time of 1 s is successfully demonstrated.

Test and Analysis of the Optical Kerr-Effect in Resonant Micro-Optic Gyros

As one kind of the main optical error sources in the resonant micro-optic gyro (RMOG), the optical Kerr-effect brings a nonzero bias to the output of the RMOG. The optical Kerr-effect induced bias error is proportional to the difference between the clockwise (CW) and counterclockwise (CCW) light-intensities input to the resonator. A new method for testing the optical Kerr-effect induced bias error in the RMOG is proposed and demonstrated. A square-wave intensity-modulated optical signal with a symmetrical duty ratio of 50% is achieved by an acousto-optic modulator (AOM), thus making the input-intensity mismatch between the CW and CCW lightwaves change periodically. In this way, we obtain the optical Kerr-effect induced bias errors that vary periodically in accordance with the variation of the square-wave signal. The experimental results show a good agreement with the theoretical value. Moreover, the testing result of the closed-loop RMOG is consistent with the open-loop one. The above method is insusceptible to other noise, such as the backscattering-induced noise and the polarization fluctuation.

Performance of closed-loop resonant micro-optic gyro with hybrid digital phase modulation

A double closed-loop resonant micro optic gyro (RMOG) employing a hybrid digital phase modulation technique is demonstrated, showing encouraging progress. In this hybrid modulation scheme, the width of one stair of the stair-like digital serrodyne wave is optimized according to the rise time of the digital-to-analogue converter to obtain the maximum sideband suppression. Based on the optimum parameters of the hybrid modulation scheme, a typical bias stability of 0.05/s in 1 hr is demonstrated in an RMOG with a silica waveguide ring resonator having a ring length of 7.9 cm. This is the best long-term performance which has ever been reported in an RMOG to our knowledge.

High finesse silica waveguide ring resonators for resonant micro-optic gyroscopes

A high-finesse silica waveguide ring resonator (WRR) is designed and a new record is demonstrated experimentally. The finesse and the resonant depth of the silica WRR with a length of 7.9 cm and a diameter of 2.5 cm are 196.7 and 98%, respectively. In addition, the silica WRR is pigtailed with single-polarization fiber to improve the polarization extinction ratio thus to reduce the polarization error. With the application of this high-finesse and high polarization extinction ratio WRR to the resonant micro-optic gyroscope (RMOG), a bias stability of 0.004°/s was observed over a one-hour timeframe.

High-frequency Pound-Drever-Hall sensing of a short and high-finesse fiber ring resonator

A resonant micro optic gyro (RMOG) equipped with a short and high-finesse fiber ring resonator employing the high-frequency Pound-Drever-Hall (PDH) modulation is proposed and demonstrated. The modulation frequency and index of the PDH modulation are optimized to maximize the slope of demodulation curve. Based on the optimum parameters, the lock-in accuracy of the resonant frequency servo loop in the RMOG is improved to 0.178°/h, which is almost improved by two orders of magnitude compared with that obtained for the low-frequency phase modulation.