sagnac和光纤陀螺

Sagnac干涉仪与光纤陀螺哈尔滨工程大学理学院光子科学与技术研究中心2007年3月SagnacEffectFirstexperimentsconcerninglightpropagationinrotatingmediawerecarriedoutbyF.Harressin1911.GeorgeSagnacpublishedhisresultsin1913andiscreditedwiththeeffectsinceHarressmadenumerouserrorsininterpretationofhisexperimentAthoughtexperiment:ctRRttRcR22LcttRcLcA()4282RcRttRRct22SagnacEffectLetusputinsomenumbers:d=10cm,A=45cm2,l=633nm,Ω=15deg/hr=7.3×10-5rad/sΔφ=4.3×10-8radB.Poganyexperimentedwithan80kgdevicetryingtorotateat1600rpm.Hereportedthatallopticalpartsweredamagedduetovibrationby600rpm.Michelsonused5milesofevacuatedsewerpipestomeasuretherotationoftheEarth.光纤陀螺（FiberOpticGyro）陀螺仪（gyroscope）作为一种主要的惯性敏感器件，用于测量运载体的姿态角和角速度，是构成惯性系统的基础核心器件，是决定其性能的关键。光纤陀螺(FOG)是一种基于Sagnac原理的光纤角速度传感器，与传统的陀螺相比，它内部没有机械旋转元件，工作启动时间短，稳定性好，寿命长，动态范围宽，质量轻，易于微型化，保持着较高的性价比。目前，光纤陀螺已经发展成为惯性技术领域具有划时代特征的新型主流仪表，其原理、工艺及其关键技术与传统的机电式仪表有很大的差别，我国已经将光纤陀螺列为惯性技术领域重点发展的关键技术之一。OpticalGyroscopesTwolaserbeamsarerotatingoppositedirectionsinaclosedloop;Whenthebeamsarecombinedtherotationrateanddirectioncanbecalculatedfromtheinterferencefringes;Twobasicprinciples:opticalresonatorandopticalinterferometer•Activeopticalresonator:LaserGyro•InterferometerFiberOpticGyro:Openloopfibreopticinterferometer(anal.)Closedloopfibreopticinterferometer(digit.)•Passiveopticalresonator:FibreopticresonatorActiveRing-laserGyroActiveopticalresonatorResonatorisalaseritself(active)Ifgyroisrotatedcounter-clockwisedirection,thecounter-clockwisebeamistravellingslightlylongerthantheoppositebeamThechangeinthepathlengthisproportionaltotherotationrateInverysmallrotationratesthereisadead-bandbecauseoffrequencylock-inLaserGyroIntroduceanactivelasermediumintothecavity.Thiseffectivelyconvertsphasechangestofrequencychanges.Theintensityismodulatedatthebeatfrequency:d=10cm,A=45cm2,=633nm,=15deg/hr=7.3×10-5rad/sn=7HzLmmcLLcLLcLALnnn()24IIto(cos())12nLaserRingGyroFiberOpticGyroToincreaseeffectivearea,wecanwindNloopsoffiberopticcable.Theoutputintensityismodulatedbythephaseshiftbetweenthetwobeams.IIo(cos())12LDcLNDFiberGyroSignalThedynamicrangeofthedeviceiseasilyconfigurableusingthelengthandthediameterofthefiberloop.Forexample,=850nm,L=1km,D=10cm=73deg/sFor1mradsensitivitym0.084deg/hForexample,=850nm,L=100m,D=3cm=2400deg/sFor1mradsensitivitym2.8deg/hcLD2互易性互易性——高精度光纤陀螺实现的保证。实际中，光纤环形干涉仪的理论噪声为1μrad/Hz1/2。光波沿100m~1km长的光纤传播时的绝对相位累计高达109~1010rad，而通过积分，可以测量10-7~10-8rad的相位差。这就意味着上述测量的稳定性需要达到10-18。如此高的测量精度和稳定性，看似不可能实现，只有借助于光波在媒质中传播的“互易性”原理来完成。光波的互易性——波动方程的共轭解。求解光波动方程可以得到相互共轭的一对解，表示他们具有完全相同的传播延迟和相前衰减，只是传播方向不同。实现方法：单模工作时，两个沿相反方向的波自动具有互易性。分束器的互易性——反射和投射次数相等。光路结构的互易性——正反传输的光波，经过相同的路径。Open-LoopInterferometricFiber-OpticGyroPolarizationmaintainingsingle-modefiberisemployedtoensurethetwocounter-propagatingbeamsintheloopfollowidenticalpathsintheabsenceofrotation.Whengyroisrotatedtherateofrotationisproportionaltothephaseshiftbetweenthebeams(Sagnacphaseshift)Open-LoopInterferometricFOG+low-price+notsensitivetoshocksandvibrations+notsensitivetogravitynoraccelerations+shortinitializationtime+goodsensitivity+thegeometryofthefibercoilisnotcritical+noneedtocontrolthelengthoftheopticalpath–verylongsinglemodefiber–thedynamicareaissmallcomparingtoring-lasergyros–driftcausedbytheanalogcomponentsSuitableforlow-costapplicationswherebestperformanceisnotrequiredHeadingof(robots,cars)TiltandrollsensingHitachiFiber-OpticGyroHitachiCableLtd.ismanufacturingone-axisopenloopfiberopticgyroscopesHitachigyrosareusedinmobileroboticsandautomotiveapplicationsDemonstratedGyroHitachiFOG-XDrift~5deg/hourClosed-LoopIFOGFormoresophisticatedapplicationslikeaircraftnavigationDigitalsignalprocessingismorecomplicatedthananalog,whichisusedinopen–loopsystemsBenefitcomparingtoopen–loopsystems:NotsensitivetolightsourceintensityvariationsNotsensitivetogainsofsinglecomponents=verysmalldrift~0.001–0.01deg/hLinearityandstabilitydependonlyfromthephasetransducer陀螺性能的基本概念陀螺在静止状态下，其输出信号可以看作是由一个噪声信号和一个缓慢变化的均值（零漂）信号的叠加。随机游走（噪声）：用单位带宽角速率的标准差表示，单位：deg/h1/2零漂：缓慢变化的均值信号的峰峰值，用deg/h表示。噪声与零票的相对重要性取决于应用场合。如对稳定性或控制用的速率陀螺，带宽相对较宽，噪声的大小相对重要。而对于导航应用来说，重要的是角速度积分后的方向信号，积分过程较低了噪声信号，使零漂显得比较重要。标度因子的线性度和稳定性。陀螺性能的基本概念GyroperformanceClassificationaccordingtobiasdriftRategrade10–10000deg/hTacticalgrade0.01–10deg/hNavigationgrade0.01deg/hDynamicarea:fewHz–500HzSourcesofNoiseFundamentalLimitationsSensitivityislimitedbyshotnoisethatgoesasthesquarerootofthepower.Thepowerreceivedatthedetectordecreaseswithfiberlength:However,theSagnaceffectincreaseswiththelengthofthefiber.Thesetwocompetingeffectssetthelengthofthefiberforagivensensitivity.Forasensitivityof10-3deg/h,Lisroughlyfewkilometers.PPeoLSourcesofNoiseThermalNoiseTimedependenttemperaturegradientalongthelengthofthefibercanintroducespuriousphaseshiftsduetothetemperaturedependenceoftheindexofrefractionandthecable.Fort=1h,D=20cm,L=1.56km,dn/dT=10-5/0C,=5*10-7/0C,n=1.45,andcalculatedshotnoiselimitof0.0078deg/h,Tneedstobe6.7*10-3/0