Linglan Wang

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.

Effect of Fresnel reflections in a hybrid air-core photonic-bandgap fiber ring-resonator gyro

A novel hybrid polarization-maintaining (PM) air-core photonic bandgap fiber (PBF) ring resonator is firstly demonstrated by using a conventional solid-core PM fiber optical coupler formed by splicing a section of PM air-core PBF into the resonator. Due to Fresnel reflections exist at the two junctions between the air-core PBF and the solid-core fiber, the forward output signal of this hybrid ring resonator is the normal resonant curve with the superposition of the lightwaves that experienced even numbers of Fresnel reflections and the backward output signal is composed of lightwaves that experienced odd numbers of Fresnel reflections. Rigorous derivations of the forward and backward output signals are given out. The biggest resonant depth and finesse of the hybrid air-core PBF ring resonator predicted are 0.352 and 6.3 respectively by assuming a splice loss of 1.8 dB per junction. These predictions are finally confirmed by testing both the forward and backward output signals of the hybrid ring resonator. With the countermeasures against the influences of the odd numbers of Fresnel reflections, a bias stability of 0.007°/s is successfully demonstrated in a hybrid PM air-core PBF ring-resonator gyro.

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.

Laser frequency noise induced error in resonant fiber optic gyro due to an intermodulation effect.

For the first time, a significant noise source in the resonant fiber optic gyroscope (RFOG) called intermodulation induced error is proposed and deeply analyzed in this paper. The intermodulation error is produced by the laser frequency noise at even multiples of the modulation frequency due to an intermodulation effect, which will seriously limit the random noise performance of the RFOG. Experiments are designed and conducted to verify and measure the intermodulation induced error in the RFOG. The experimental results confirm the existence of intermodulation error, and fit well with the theory. As for the design of the RFOG, light sources with a narrow intrinsic linewidth and a high modulation frequency are preferable to achieve a high rotation-rate sensitivity.

Resonant fiber optic gyro based on a sinusoidal wave modulation and square wave demodulation technique

New developments are made in the resonant fiber optic gyro (RFOG), which is an optical sensor for the measurement of rotation rate. The digital signal processing system based on the phase modulation technique is capable of detecting the weak frequency difference induced by the Sagnac effect and suppressing the reciprocal noise in the circuit, which determines the detection sensitivity of the RFOG. A new technique based on the sinusoidal wave modulation and square wave demodulation is implemented, and the demodulation curve of the system is simulated and measured. Compared with the past technique using sinusoidal modulation and demodulation, it increases the slope of the demodulation curve by a factor of 1.56, improves the spectrum efficiency of the modulated signal, and reduces the occupancy of the field-programmable gate array resource. On the basis of this new phase modulation technique, the loop is successfully locked and achieves a short-term bias stability of 1.08°/h, which is improved by a factor of 1.47.

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.

Resonant fiber optic gyro based on total internal reflection photonic crystal fiber ring resonator

We realize the first optical-fiber “meta-tips” implementing in the near-infrared the beam-steering with increasing angles, up to the limit case of surface-waves excitation. We also explore their capability to work as local refractive index sensor.

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.

Hybrid air-core photonic bandgap fiber ring resonator and implications for resonant fiber optic gyro

A novel hybrid polarization-maintaining (PM) air-core photonic bandgap fiber (PBF) ring resonator is demonstrated by using a conventional PM fiber coupler formed by splicing a section of air-core PBF into the resonator. The coupling loss between the PM air-core PBF and the conventional solid-core PM fiber is reduced down to ∼1.8 dB per junction. With the countermeasures proposed to reduce the backscattering induced noise, a bias stability of approximately 0.007 °/s was observed over a 1 hour timeframe, which is the best result reported to date, to the best of our knowledge, for RFOGs equipped with a hybrid air-core PBF ring resonator.