Search

Abstract: A resonator fiber optic gyro is a high accuracy inertial rotation sensor based on the Sagnac effect. Fiber ring resonator is the core-sensing element in the resonator fiber optic gyro. The dynamic response of the resonator has been studied, and the ringing phenomenon is observed when sweeping the laser frequency. The dynamic characteristics of the resonator, which are related with the frequency sweep rate, have a decisive effect on the dynamic performance of the gyro system. In order to further analyze and better design the gyro system, deep analysis of the dynamic resonance characteristics is in urgent need. This paper gives out the condition for the ringing phenomenon, and analyzes the parameters for the ringing and the dynamic resonance curve through simulation. It is concluded that increasing the sweep rate will lift the ringing and deteriorate the parameters of the resonance curve, and finally have negative effects on the performance of the gyro system. [Copyright &y& Elsevier]

Based on the digital bipolar serrodyne and sine phase modulations, a closed-loop RFOG with two LiNbO 3 phase modulators is proposed and studied. Through theoretical simulation, the bipolar serrodyne waveform is optimized to improve the detection sensitivity. By the characteristic analysis of the practical serrodyne phase modulation spectrum, the sine modulation frequency is optimized to reduce the two loops' spectrum overlapping, which would lead to the backscatter noise. The optimization result is verified by the gyro output signal tests under the different sine phase modulation frequencies. It is concluded that in order to avoid the spectrum overlapping, the difference between the sine modulation frequency and serrodyne modulation reset frequency should be properly increased, and the sine modulation frequency is required to be close to an even multiple of the serrodyne modulation repetition frequency. Finally, using the optimized phase modulation parameters, the gyro output signal is tested with an integration time of 0.1 s over 1 h, and the bias stability around 7.1 deg/h based on the Allan deviation analysis is obtained. [ABSTRACT FROM AUTHOR]

In this paper, how the phase modulation index’s drift affects an open-loop resonator fiber optic gyro’s (RFOG’s) performance is discussed. By using the ratio of the second to fourth harmonic (2nd/4th harmonic), a harmonic feedback technique is proposed to suppress this drift. It is found that the phase modulation index’s drift would lead to a significant measurement error, which increases with rotation rate. It is proven that there exists an approximately linear correlation between phase modulation index and 2nd/4th harmonic. Using this correlation, the 2nd/4th harmonic feedback technique is applied to the open-loop RFOG to stabilize the phase modulation index. Although the phase modulation index slightly deviates from its optimal value in the dynamic state with this technique, it is proven that the induced backscatter noise could be neglected. The test results indicate that the phase modulation index’s drift with this technique is reduced to about 22% of that without suppression technique, and the stabilities of gyro output signal are respectively improved by about 29% and 31% under 5deg/s and 10deg/s when this technique is used. It is concluded that the 2nd/4th harmonic feedback technique does work in suppressing the phase modulation index’s drift. [ABSTRACT FROM AUTHOR]

Based on second harmonic difference between two counter-propagating beams, a harmonic subtraction technique is proposed to suppress the intensity modulation induced Kerr effect drift in a closed-loop RFOG. The linear relationship between Kerr effect induced drift and second harmonic difference is established, and based on this relationship, the harmonic subtraction algorithm is proposed. The intensity modulation induced Kerr effect drift is tested in the practical closed-loop RFOG, and it is found that the intensity modulation does cause a significant Kerr effect drift, which becomes larger as the initial second harmonic difference increases. The tests for gyro output signal are carried out with harmonic subtraction technique to verify its effectiveness. It is indicated that this technique could achieve a noise suppression ratio of better than 7.95%. It is concluded that the harmonic subtraction technique really works in suppressing the intensity modulation induced Kerr effect drift in a closed-loop RFOG. [ABSTRACT FROM AUTHOR]

Aiming at the demodulation signal compensation technique for intensity modulation noise suppressing in a digital RFOG, which is based on the detection of closed loop’s second-harmonic, the quantization precision for second-harmonic is discussed and optimized. By analyzing second-harmonic’s fluctuation under the intensity modulation noise equal to shot noise limited sensitivity, the expression for the required minimum quantization bits of second-harmonic signal is obtained. Based on this expression, numerical simulations are carried out to optimize the quantization bits in a digital RFOG in detail. Based on over-sampling technique, the stability of gyro output signal with different quantization bits and rotation rates is tested to verify the theoretically analyzed results. It is concluded that the minimum quantization bits of second-harmonic is related to the rotation rate and the ratio of second-harmonic’s maximum to minimum, and it gets larger as these two parameters are increased. Especially, the required minimum quantization bits for second-harmonic would generally exceed that supported only by hardware circuits, which leads to the adoption of over-sampling technique. And it is proven that the quantization precision improvement for second-harmonic, realized by the over-sampling technique, does work in improving the effect of intensity modulation noise suppressing. [ABSTRACT FROM AUTHOR]

A harmonic division technique is proposed for an open-loop resonator fiber optic gyro (RFOG) to suppress semiconductor laser diode's (LD's) intensity modulation noise. The theoretical study indicates the RFOG with this technique is immune to the intensity noise. The simulation and experimental results show this technique would lead to a diminished linear region, which still could be acceptable for an RFOG applied to low rotation rate detection. The tests for the gyro output signal are carried out with/without noise suppressing methods, including the harmonic division technique and previously proposed signal compensation technique. With the harmonic division technique at the rotation rate of 10 deg/s, the stability of gyro output signal is improved from 1.07 deg/s to 0.0361 deg/s, whose noise suppressing ratio is more than 3 times as that of the signal compensation technique. And especially, a 3.12 deg/s signal jump is significantly removed with the harmonic division technique; in contrast, a residual 0.36 deg/s signal jump still exists with the signal compensation technique. It is concluded the harmonic division technique does work in intensity noise suppressing under dynamic condition, and it is superior to the signal compensation technique. [ABSTRACT FROM AUTHOR]

A miniaturized compact open-loop resonator fiber optic gyro (RFOG) prototype with main body size of about 10.4 cm×10.4 cm×5.2 cm is reported, and a demodulation signal compensation technique is proposed, aiming to suppress the drift arising from accompanying intensity modulation induced by semiconductor laser diode (LD). The scheme of how to establish this miniaturized RFOG prototype is specifically stated. The linear relationship between the first-harmonic and second-harmonic demodulated signals respectively for the two counter propagating beams in the resonator is verified by theory and experiment, and based on this relationship, the demodulation signal compensation technique by monitoring the second-harmonic demodulated signal is described in detail. With this compensation technique, the gyro output stability under 1°/s rotation rate is effectively improved from 0.12°/s to 0.03°/s, and especially, an about 0.36°/s peak-to-peak fluctuation due to tuning current reset is significantly suppressed. A long term bias stability of about 4.5°/h in 1 h for such a small-sized RFOG prototype is demonstrated, which is of the same magnitude as that of currently reported large-sized RFOG systems utilizing LD as the laser source as well. [ABSTRACT FROM AUTHOR]

Abstract: Resonator Fiber optic gyro (RFOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. The optical fiber ring resonator (OFRR) is the key rotation sensing element. The backscattering characteristics of the OFRR are fully investigated. The Rayleigh backscattering dominates the backscattering spectrum with the input power below the threshold. High carrier suppression is crucial to reduce this Rayleigh backscattering error. Being different from the intrinsic Rayleigh scattering of the fiber, the stimulated Brillouin scattering (SBS) in the OFRR should be avoided. This is because the finesse and the resonance notch depth of the OFRR decrease for the pump depletion through the SBS process. The shot noise limited sensitivity (SLS) of the RFOG is improved by increasing the input power. Through analysis, it is found that the threshold input power is improved after phase modulation. The SLS of the RFOG is analyzed at different modulation parameters and its relevant SBS threshold. Accordingly, the optimized modulation frequency and the corresponding maximum input power are all obtained. A simple method of testing the frequency shift in the SBS is also proposed. In this method, the central frequency of the laser source is locked to the resonance frequency of the OFRR in one direction. A steady SBS light is observed and its frequency shift is measured together. [Copyright &y& Elsevier]

Resonator fiber optic gyro (R-FOG) is a promising candidate for the next generation inertial rotation sensor whose resonant frequency is changed due to the Sagnac effect. Observed from the resonance curve, the free spectral range of the resonator, the full width at half maximum of the resonance curve, the finesse of the resonator, and the resonance depth are 35.7 MHz, 2.21 MHz, 16.2, and 0.95, respectively. In the experiment, there is an acoustic-optical modulator (AOM) in each light loop. When the frequency of the fiber laser is locked to the resonance frequency in the counterclockwise direction, the frequency difference between the driving frequencies of the two AOMs is equivalent to the frequency deviation caused by the gyro rotation. In this locked condition, the gyro dynamic range calculated from the demodulation curve in the clockwise direction is from 13.5 to −13.5 rad/s. From the signal-to-noise of the average intensity arriving in the photodiode, it can be estimated that the shot-noise-limited sensitivity of mis system will be . [Copyright &y& Elsevier]