Research On Resonator Fiber Optic Gyroscope Based On Novel Photonic Crystal Fiber

Resonator fiber optic gyro?RFOG?as the second generation of FOG obtains rotation angular by detecting the resonant frequency difference between clockwise and counterclockwise directions in a fiber ring resonator.To achieve the same accuracy,the necessary length of fiber coil in RFOG theoretically is only one of tens or hundreds of that in IFOG,and therefore RFOG is highly competitive in the future development of miniaturization,integration and low cost of FOG.However,the performance of RFOG is limited due to the influence of optical noises in the fiber ring resonator,such as back scattering noise,polarization fluctuation noise and so on.Photonic crystal fiber?PCF?,characterized with radiation insensitivity,high thermal stability,and good polarization mainting ability,shows great potential in the field of FOG.In this article,considering the superior performance of PCF and advantages of RFOG,we put forward to apply the PCF into RFOG,and conduct a study on some key problems,such as the structure optimization of PCF resonator,the backscattering noise suppression,the modulation and demodulation technique of phase modulation spectrum,and the polarization fluctuation noise suppression.Meanwhile,considering the development of new type of PCF and its potential applications in RFOGs,we also discuss the novel type of PCF structure and analyze its characteristics.The main contents of this article are as follows:?1?In order to design a high performance PCF resonator,the resonator transmission characteristics and the relationship between its performance and structural parameters are studied.The amplitude condition and phase condition for the optimum resonant state in the fiber resonator are deduced,and the influence of the structure parameters on the output light intensity,the circularing light intensity and the fineness of the resonator is further analyzed,which provides a theoretical basis for optimizing the resonator structure.Considering the influence of the linewidth of laser spectrum and large splice loss of PCFs,we also analyze the limit sensitivity of RFOG determined by the shot noise of photodetector.It is found that the fineness and theoretical limit sensitivity are limited because of the large splicing loss between the PANDA tail fiber of the coupler and PCF.Further,the mode matching technique is analyzed and applied to reduce the splice loss,and the test results show that the splicing loss of the PCF is reduced by the mode field matching technology,which improves the fineness of PCF resonator to a certain extent.?2?For the issue of backscattering noise in RFOGs,the mechanism and suppression method are analyzed.In order to reduce the influence of backscatter interference noise,we firstly invesetigate impacts of modulation parameters on the carrier component,spectrum distribution and carrier suppression ratio in the carrier suppression technique.In order to estimate the gyro bias caused by the backscatter noise,a test platform is built to measure the backscattering coefficients of PCF and PANDA fiber resonators.The test results show that the backscattering coefficient of the PCF cavity is relatively small.In addition,the theoretical simulation shows that if the carrier suppression ratio of modulation signal meets certain requirements,the gyro bias caused by back scattering can be reduced to the order of theoretical limit sensitivity.?3?The signal detection process of RFOG is deeply and comprehensively analyzed,and the dynamic response model of resonantor with phase modulation spectroscopy technique is established,and the impacts of the modulation parameters on the dynamic response of the PANDA fiber and PCF resonator are discussed.The results show that there is a serious overshoot phenomenon in the dynamic output waveform when the modulation frequency gradually increases.When the modulation frequency is too large,the linearity of the demodulation curve becomes worse,and then the dynamic range of the gyro output is limited.Compared with the PANDA fiber resonator,the PCF RFOG has a larger theoretical dynamic detection range,but the smaller slope of the demodulation curve in PCF RFOG means lower detection sensitivity.Finally,the experimental platform of signal detection based on phase modulation spectrum is set up,and the theoretical model is verified.?4?The polarization characteristics of optical fiber resonator are studied by the Jones matrix method,and the impact of the splice misalignment angle and temperature change on eigenstates of polarization and the inclined angle of its principal axis are dicussed in detail.The results show that the eigenstates of polarization of the resonator is affected by many factors,and may be linear polarization,elliptical polarization,or circular polarization.When the phase difference caused by the temperature is an integer multiple of 2?,the principal axis will deviate from the polarization axis of the fiber to the greatest extent.After,the influence of temperature change on the resonance curve is theoretically and experimentally analyzed,and find that the separation distance between the resonance curves of two eigenstates of polarization varies with different temperatures,which is verified by the actual test.In addition,to meet the requirement of high birefringence for RFOG,a new type of hight birefringence PCF with the defected core is designed.The simulated results show that the birefringence of the proposed PCF can reach 10^-2 order of magnitude.?5?In view of the polarization crosstalk in the traditional polarization maintaining coupler,a novel single-mode single-polarization PCF coupler with dual cores is designed.We apply the full vector FEM and beam propagation method?BPM?to investigate its property,including fundamental space-filling mode?FSM?,single polarization operating region and coupling charateristics.The simulated results show that the single polarization region can be freely tunned by adjusting the structure parameters,and it possesses a wide bandwidth of the single polarization region.It provides a potential solution to suppress the fluctuation noise caused by polarization crosstalk in conventional polarization maintaining couplers.