Study On The Absolute Length Measurement Based On Cross Correlation Of A Femtosecond Optical Frequency Comb

Large-scale precise equipment manufacturing such as satellites and aircrafts is one of the most important developement direction of advanced manufacturing.So we have to study new large-scale length measurement method with high efficiency and wide dynamic range to satisfy requirements from industry.Laser is a powerful tool for length measurement after it was developed.The development in laser sources will obviously boost length measurement research.Femtosecond optical frequency comb is a new pulse laser source invented in 21 st century,it's a powerful tool for high-percision distance measurement with its advantages like ultra-fast pulses,stable optical spectrum,abundant modes,potential for traceability and so on.Aiming to find a new length measurement method which could satisfy large-scale measurement requirements from industry,we studied several important methods of absolute distance measurement based on cross correlation of a femtosecond optical frequency comb in this thesis.First-and second-order cross-correlation functions were analyzed detailedly and simulated with numerical models.The influence of dispersion was studied.Then,we proposed a strategy to choose the cross-correlation function for different measurement applications.After that,acquisition error in cross-correlation functions caused by translation stages was analyzed.To solve this problem,a compensation method based on interference fringes was proposed.Finally,distance measurement based on optical sampling by cavity tuning was studied and all methods were proved by experiments.The main contents are as follows:1.Requirements of distance measurement from advanced manufacturing and limitations of traditional methods were analyzed.Besides,backgrounds,properties and advantages of the femtosecond optical frequency comb were introduced.Researches on distance measurement based on comb were summarized.2.Numerical models of first-and second-order cross-correlation functions were established after studying basic principle.The influence of dispersion was studied and a strategy to choose the cross-correlation function was proposed.3.Pulse-to-pulse alignment based on cross-correlation functions was studied by comparing hilbert transform and gaussian fitting.A method was proposed to compensate cross-correlation functions obtained by translation stages.Then time of flight by scanning reference beam was analyzed deeply.4.To improve measurement efficiency,optical sampling by cavity tuning was studied.After uncertainty analysis of the whole measurement system,the importance of long fiber stabilization was proved clearly.With long fiber stabilized by an optoelectronic oscillator,the design scheme was proposed.5.Experimental platform was established to verify methods proposed above.First,a standard rule of 1.5 meter was built by time of flight with an uncertainty better than one micrometer.Second,optical sampling by cavity tuning method was proved with a setup in which there was an optical path difference of about 1500 m,then absolute distances were measured in a range of 22 mm with an uncertainty of several micrometers.