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Research On Key Deyices In Resonator Fiber Optic Gyroscope

Posted on:2014-09-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:X H YuFull Text:PDF
GTID:1268330425481390Subject:Microelectronics and Solid State Electronics
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Fiber optic gyroscope is a high accuracy inertial rotation sensor based on the Sagnac effect. It plays an important role in the field of navigation and guidance. A resonator fiber optic gyroscope (RFOG) has the potential to achieve the inertial navigation system requirement with a short sensing coil. It is a good choice of the fiber optic gyroscope with a small volume and light weight.To improve the stability and linear dynamic range of the RFOG, the dissertation will do the reaserch on the laser frequency noise, polarization noise and closed detection. The main innovational work and achievements are further highlighted as follows:(1) A highly coherent light source is a key component in the RFOG. The possibility of employing a miniature semiconductor laser in the RFOG is investigated both theoretically and experimentally. The phase modulation spectrum technology is always used in the RFOG for achieving a high sensitivity detection. Both the theoretical analysis and the experimental results show that the laser frequency noise is amplitude modulated to the modulation frequency, which is a huge noise source for the RFOG. To suppress the laser frequency noise, an active frequency stabilization is applied in the dissertation. The model of the stabilization loop and the related loop parameters, including the loop (direct current) gain, the loop delay and the low-pass filter, are also demonstrated. Benefiting from the high finesse fiber resonator, an on-line and sensitive laser frequency noise observation compatible with the RFOG itself is built, as a powerful optimum criterion for the loop parameters in the experiment. With the help of the built observation window, we improve and optimize the loop, and decrease the laser frequency noise down to0.021Hz (lα) for the integration time of10s, which is equivalent to a rotation rate of0.07°/h, and close to the shot noise limit for the RFOG. This successful work provides a promising technical solution to the miniaturization of the laser source in the RFOG.(2) A novel fiber ring resonator is configurated by inserting two in-line polarizers in a polarization-maintaining fiber (PMF) resonator with twin90°polarization-axis rotated splices. This solution effectively solved the temperature-related polarization noise that has restricted the long-term stability of the RFOG. Using the Jones Matrix, a simulation model used to analyze the thermal-related poarization charactersitics in the resonator is set up. Both the theoretical analysis and the experimental results show that this novel polarizing resonator is insensitive to environmental temperature variations. Then, an RFOG empolying this novel polarizing resonator is built. The total fiber length of the resonator is14m. A stable open-loop output in an hour is achieved with the random walk coeffcient of0.083°/h and the bias stability below1°/h.When the temperature of the resonator is changed from36.2℃to33℃in eight minutes, the open-loop gyroscope output is stable and do not drift with the temperature. It shows that the polarization-fluctuation noise is suppressed and the long-term stability of the RFOG is improved effectively by employing this novel resonator. To the best of our knowledge, these results are the best ever demonstrated in an RFOG in a temperature varied environment.(3) An improved frequency shifting module is designed and constructed on a LiNbO3phase modulator. Its frequency resolution is reduced to0.01Hz/LSB and frequency shifting range is widend to±1.25MHz. With the frequency shifter applied in the RFOG, a closed-loop detection is demonstrated, whose bias stability is around2.1°/h approximately equal to that of the open-loop output. Compared to the open-loop detection, the closed-loop RFOG has a wider linear range and a lower scale factor nonlinearity. The measured result shows that the open-loop linear detection range of±215°/s is improved to±1076°/s. It is improved by a factor of5. The open-loop scale factor nonlinearity of1.2%is decreased to0.02%(200ppm), which is improved by a factor of60.In a word, the gyro bias stability below1°/h is successufully demonstrated by suppressing both the laser frequency noise and the polarization-fluctuation noise. Good linearity is also achieved thanks to the closed-loop detection. These achievements open up the possibility to the commercialization of RFOG.
Keywords/Search Tags:Resonator fiber optic gyroscope, Laser frequency noise, Polarizationnoise, Fiber resonator, Closed-loop detection, High accuracy frequency shifter
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