Research On IFOG Light Path Noise’s Suppression And Correlation

High performance interference fiber optic gyroscope (IFOG) adopt all digital close loopcontrol scheme. The components of light path are erbium-doped super fluorescent fibersources (SFS), single mode optic fiber coupler, integrated optical chip (Y waveguide) andpolarization maintaining fiber ring. SFS has wide spectral type, stable wavelength and highpower. Ceteris paribus, high power means high signal noise ratio (SNR), but the SNR will notincrease when the light power reaches a threshold value, in order to improve IFOG’sprecision it is necessary to depress the noise of light source. This thesis analysis themechanism of light source noises, propose a method to depress them. The work includefollowing aspects:First, the Sagnac effect and reciprocity principle were introduced. It adopt step wave asmodulation wave, four state square wave as offset wave.Secondly, all kinds of light path noises were analyzed and the structural model of lightsource was established in light-emitting mechanism. In erbium-doped fiber the concentrationof Er3+can affect the performance of light source, so it is important to control theconcentration. Then the mechanism of thermal noise, shot noise and relative intensity noise(RIN) were researched in chapter three. For low values of detected signal power, RWC ofIFOG will be dominated by shot noise, however, when detected signal power is greater than afew microwatts, RWC will be dominated by RIN. Thus for high power SFS light source inhigh precision FOG, it is necessary to reduce RIN.Thirdly, when cross-correlation coefficient between FOG’s output and coupler’s freeport signal is low or the delay of interference signal is not precisely evaluated, RIN willincrease after noise subtraction. According to this situation, the relation betweencross-correlation coefficient and noise subtraction’s result was analyzed theoretically, and amethod of pre-estimate noise subtraction’s result by using signal cross-correlation waspresented. This will enhance the reliability of IFOG.Lastly, a model of IFOG was built by using MATLAB/Simulink, a simulation with therealistic parameters was carry out and result shows that noise subtraction can enhance IFOG’sperformance.