Parameters optimizationofinterferometricfiberopticgyroscopeforParameters optimization of interferometric ?ber optic gyroscope for improvement of random walk coef?cient degradation in space radiation environmentJing Jin n ,Song LinSchool of Instrument Science and Opto-electronics Engineering,BeiHang University,Beijing 100191,Chinaa r t i c l e i n f oArticle history:Received 17April 2012Received in revised form 5June 2012Accepted 5June 2012Available online 29June 2012Keywords:Fiber optic gyroscope Radiation effectsRandom walk coef?cient Parameter optimizationa b s t r a c tA random walk coef?cient (RWC)prediction model of interferometric ?ber optic gyroscope (IFOG)in radiation environment has been developed,combining a radiation-induced attenuation (RIA)model of ?ber and a RWC expression of digital closed-loop IFOG,and veri?ed by the radiation experiments results of two ?ber coils and an experimental http:/www.wendangku.net/doc/daec004058fafab068dc0225.htmling the RWC prediction model the effects of source power,?ber length and modulation phase on the RWC of IFOG were investigated in space radiation environments.Based on the prediction model and its parameters analysis,a parameters optimization method was proposed for IFOG design to improve the RWC degradation in space radiation environments.Finally,the three parameters of the experimental IFOG were redesigned according to the optimization method.&2012Elsevier Ltd.All rights reserved.1.IntroductionRecently,the space industry is increasingly showing a lot of interest in using IFOG because of their high performance,low weight,low power consumption and high reliability 13.However,during their stay in orbit,the IFOG components face a harsh radiative environment of various types.The most important effects of radiation on optical heads include the increase of ?ber attenuation and the fall-off of source power and detector responsivity,which would cause RWC degradation and bias drift on IFOG 37.In-orbit calibration can compensate most of the long-term bias drift,but not improve the RWC performance 4,8,9.The RWC degradation must satisfy the requirement for application over the whole mission time.Therefore,RWC prediction in space radiation environment,parameters margin design and vulnerable parts redundancy are indispensable measures to increase IFOG lifetime and reliability 3,4.The main idea of this paper is to propose a parameters optimization method for IFOG design in order to improve the radiation-induced RWC degradation of IFOG in space.A novel prediction model of RWC was developed to predict measure-ments at a given dose rate,and how the RWC of an IFOG might be affected by radiations at lower dose http:/www.wendangku.net/doc/daec004058fafab068dc0225.htmling this prediction model,we analyzed the effects of source power,?ber length and modulation phase on the RWC degradation in space radiationenvironment.Based on this analysis,a parameters optimization method was proposed for IFOG design to guarantee the RWC performance during whole space mission.2.RWC prediction modelThe most relevant noise sources affecting optoelectronic sys-tems performance may be listed as shot noise,source intensity noise,thermal noise in the detector load resistor and dark current noise in detector 10,11.To take an account of these noises,RWC of the digital closed-loop operational IFOG with square wave modulation can be expressed as 1,7,10RWC ?l c2p LD ?2e e1tcos f T2I esin f Tte1tcos f T2D v esin f Tt2el d eI sin f Tt4kTR eI sin f T,s e1Twhere k is the Boltzmann constant,T is the absolute temperature,e is the electron charge,D v is the source spectral bandwidth in the frequency domain,l is the wavelength of light,c is the light speed in vacuum,R is the detector load resistance,I d is the detector dark current,L is the length of ?ber coil,D is the diameter of ?ber coil,f is the modulation phase,and I is the detected photocurrent and can be expressed as I ?Z P o 10?A c teA i tA TL =10,e2Twhere P o is the source power coupled to the optical circuit,Z is the responsivity of the detector,A is the radiation-inducedContents lists available at SciVerse ScienceDirectjournal homepage:http:/www.wendangku.net/doc/daec004058fafab068dc0225.html/locate/optlasengOptics and Lasers in Engineering0143-8166/$-see front matter &2012Elsevier Ltd.All rights reserved.http:/www.wendangku.net/doc/daec004058fafab068dc0225.html/10.1016/j.optlaseng.2012.06.004nCorresponding author.E-mail address:jinjinghttp:/www.wendangku.net/doc/daec004058fafab068dc0225.html (J.Jin).Optics and Lasers in Engineering 50(2012)15421547attenuation (RIA)of ?ber coil in dB/km,A i is the initial ?ber coil loss in dB/km,and A c includes all the other optical circuit losses due to the ?ber couplers,IOC and splices.The RIA in a ?ber obeys a