Suppression Of Optical Noises And Signal Detection Technique Of Resonant Fiber Optical Gyro

Resonant fiber optical gyro is an angular velocity transducer base on Sagnac effect.With the strength of anti-abrasion,wide dynamic range,no preheating time,great resistance to shock,easy to miniaturization,low cost and so on,there is a huge market application prospect,it quickly became a research hot spot.However the optical signal base on Sagnac effetion is extremely weak,thus it is very easy to be covered in noise.Therefore,suppress the influence of noise to improve accuracy of resonant fiber optical gyro is of great importance.For the problem of backscattering noise,polarization noise and demodulation technique,this paper's research contents and achievement is as following.The backscattering noise is constituted by Rayleigh backscattering and stimulated Brillouin scattering,its influence including the backscattering intensity itself and the interference between backscattering lightwave and signal lightwave.The source of Rayleigh backscattering is nonuniform spot in fiber,including the melting point,thus its triggering condition is similar to random,which leads to a huge fluctuation of backscattering power.As for stimulated Brillouin scattering,it is caused by electrostrictive effect,which is introduced by excess optical power,its triggering condition is steady,therefore the fluctuation of stimulated Brillouin scattering power is usually small.In this paper,a backscattering detecting optical path is built,on the basis of backscattering power fluctuation,Stimulated brillouin scattering threshold power is acquired,which is 5.90 mW.As to Rayleigh backscattering,a common suppression is to modulate the optical signal in different frequency,and optimize the voltage amplitude of modulation wave to suppress the carrier amplitude.The relationship between the modulation voltage and carrier amplitude can be obtained through the self heterodyne optical pathway.This paper inferred the transmission process of the optical wave in self heterodyne optical pathway to confirm the feasibility of this experiment and finally the optimal carrier suppression voltage value is obtained.The resonant signal is smoother than unoptimized modulation and linearity of linear region is improved by three times.The source of polarization noise is the unexpected error of coupler in optical system,it causes a polarization coupling,both two polarization eigen states will exist in resonant ring.Also,the environment changing may lead to the birefringence changing,thus the phase difference between two polarizations is not stable,eventually the two polarization will disturb each other and influence the dectection.The influence,characteristic and source of polarization noise is analysed and two main cause of polarization noise is polarization coupling and polarization phase instability.This paper choose the reflecting resonant ring as construction,and rotated polarization axis in 90 degree to suppress the polarization noise.In experiment,the polarization ratio error of resonant ring is about 0.653%,after using sawtooth wave to scan the frequency of laser module,resonant depth fell by 50% to 0.4975,demodulation linearity is 0.001238.Within the temperature range of to,the total FSR fluctuated around 3.084 MHz,standard deviation is 0.194.And the relative distance of two polarization eigenstate is maintaining between 2.72 rad and.A common demodulation technique for sinusoidal modulation is CORDIC algorithm.For the problem of FIR filter such as(1)FIR filter occupies too much resource in FPGA,(2)filter parameter is difficult to design,(3)using demodulation curve from CORDIC algorithm will easily influenced by zero wander,this paper proposed a new demodulation technique to obtain the amplitude of overlaid sinusoidal wave in resonant signal by sampling and subtracting,using this amplitude as error input can avoid from zero wander.,Due to fluctuation of resonant curve caused by sinusoidal wave modulation,an algorithm to acquire the judgment of entering in the resonant valley is designed in this paper,the locking module can achieve a fast locking time using the judgment In the experiment,the locking time of 2.77 ms is obtained,and the steady state error of frequency locking is °.At last,a self scan module is designed to recalculate judgment of entering in the resonant valley due to the fluctuation of laser optical power,which enhenced the stability of gyro system.After optimizing,the scale factor of gyro is 22.22,under 10 s integral time,the zero bias is and zero-bias stability is.