Lishuang Feng

Transmissive resonator optic gyro based on silica waveguide ring resonator

A transmissive resonator optic gyro (TROG) based on silica waveguide ring resonator with improved long-term bias stability is reported in this paper. The modeling of a transmissive resonator used in optic gyro is carried out. The polarization dependence of resonator and the influences of phase modulators residual intensity modulation on the gyro output are analyzed. The resonator is simulated, designed, fabricated, tested and used to build up a TROG prototype. A bias stability of 0.22°/s over one hour test with an integration time of 10s is successfully demonstrated. No obvious drift has been found from the Allan variance analysis result of a 10000s test data, which means that the TROG prototype has an improved long-term drift characteristic.

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.

Suppression of backreflection error in resonator integrated optic gyro by the phase difference traversal method

The phase difference traversal (PDT) method is proposed to suppress the backreflection-induced error in resonator integrated optic gyro (RIOG). Theoretical analysis shows that the backreflection-induced zero-bias fluctuation is periodical and sine/cosine-like. By forcing the phase difference between the CW and CCW incident light to traverse the interval [0, 2π] repeatedly and rapidly enough, the fluctuation can be low-pass filtered and, hence, the backreflection-induced error can be effectively suppressed. A RIOG apparatus is built up, with multi-wave hybrid phase modulation to traverse the phase difference and in-phase modulation to set the operation point. A short-term bias stability of 0.0055 deg/s and a long-term bias stability of 0.013 deg/s are successfully demonstrated which, to the best of our knowledge, are the best results reported to date for the buried-type silica waveguide ring resonator-based RIOG.

High-Stability Er-Doped Superfluorescent Fiber Source Incorporating Photonic Bandgap Fiber

A tunable photonic bandgap fiber filter was incorporated in an Er-doped superfluorescent fiber source to improve its mean wavelength thermal stability. This simple filter was able to successfully compensate the mean wavelength to less than 10 ppm from −40 °C to 70 °C. When the environmental temperature was controlled to ±0.5 °C, the SFS exhibited a long-term mean wavelength stability of ±1 ppm over 11 hours. With 60 mW pump power at 974.2 nm, an optimal Er-doped fiber length of 8m was found, and the final output power of the compensated SFS reached 8 mW.

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 angle random walk by in-phase triangular phase modulation technique for resonator integrated optic gyro

In a resonator integrated optic gyro (RIOG) employing a planar optical waveguide ring, the interference between backreflected light and signal light will not only cause nonreciprocal drift of cw and ccw resonance frequencies, but also deteriorate the original signal waveform of the resonator output. If contra-phase triangular phase modulation (CPM) were applied, a cosine-like ripple, whose initial phase varies randomly, would superpose upon the quasi-square waveform of the resonator output, resulting in increment of noise and the gyros angle random walk (ARW). Therefore, in-phase triangular phase modulation (IPM) technique is proposed and used to eliminate the ripple and improve the waveform quality of the resonator output, and the gyros ARW is obviously reduced from 3 to 0.8 deg/h1/2 compared to that of CPM. This enlightens a new way to design the scheme of backreflection/backscattering suppression.

A Generally Optimized FDTD Model for Simulating Arbitrary Dispersion Based on the Maclaurin Series Expansion

An optimized solution to the discrete numerical model for simulating arbitrary dispersion by the finite-difference time-domain (FDTD) method is derived for both the single-pole and two-pole frequency responses of dispersive media. Based on the method of Maclaurin series expansion, the derivation is aimed to suppress the redundant truncation errors into minimum levels by eliminating the first several series terms of difference between the numerical and theoretical solutions to a modeled susceptibility. The accuracy of numerical approximation to theoretical dielectric functions based on our proposed approach is shown to be exactly equivalent to the bilinear transformation model for the single-pole dispersion response of the modeled dispersive material, but higher than those of other two previously reported models for a two-pole dispersion response of a modeled dispersive material. The explicit coefficients of the proposed model for several classical types of dispersive materials are derived and their corresponding dominant truncation errors are given as well. Both the analytical and simulation results obtained from the FDTD modeling of an exemplified material, silver, demonstrate that the new model outperforms the other models when they are incorporated into the fourth-order accurate FDTD algorithm with small numerical dispersion error rather than in the second-order one with large numerical dispersion error.

Design of Out-of-Plane MOEMS Accelerometer With Subwavelength Gratings

A novel out-of-plane MOEMS accelerometer based on near-field evanescent wave coupling by means of variable period subwavelength gratings has been proposed. First, the diffraction order number was calculated. Then, structure parameters were optimized by finite element analysis to achieve high sensitivity in an ideal vibration mode. Results show that the accelerometer has displacement sensitivity at 2033 nm/G with a measurement range of 0.12 G, corresponding to first diffraction beam optical sensitivity 0.46%/mG. Finally, we designed the fabrication method to form such MOEMS accelerometer and successfully fabricated the uniform and well-designed subwavelength gratings with the period of 1.0 μm by FIB/SEM dual beam system. The subwavelength gratings fabricated are very close to those designed within the experimental error to lay the foundation for the subsequent fabrication. These results provide a theoretical basis for design and fabrication of an out-of-plane MOEMS accelerometer with subwavelength gratings.

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.