Research On The Setup Of Spacial Distance Standard Based On The Temporal Coherence Detection Of The Femtosecond Laser Source

Length is one of the seven physics constants,meanwhile length is the most essen-tial information in the mechanical geometrical measurement.From spatial coordinates systems?e.g.GPS,Beidou Satellite?,to three-dimentional coordinate measurement sys-tems on the manufacturing technology,even on the micro-nano scale observation sys-tems,length measurement serves the critical role.Femtosecond optical frequency comb?FOFC?opens a new era for the length measurement,the length and time information could be directly linked with it,as a result of which,the measurement results are traced to the definition of meter.Based on the its narrow pulse width and the broad spectrum features,varieties of absolute distance measurement techniques have mushroomed re-cently.As a novel absolute distance measurement technique,coherence detection in the time domain has plenty of advantages over other techniques,such as the measurement resolution within a pulse length,simple structure setup,wide range of measurement.All these advantages make it more suitable to set up a spatial distance standard in the large scale space.This paper has studied key techniques on the spacial distance standard setup based on the first order coherence detection.The main research contents are as follows:1.After the analysis of the principle of first order coherence detection,the paper lists the advantages and disadvantages of phase measurement method and the time of flight measurement method.In this paper,the first order coherence detection is analyzed,the influences of ambient factors?temperature,humidity,pressure?and system error on measurement precision are analyzed.The absolute distance measurement experiment are designed and performed,within the measurement distance of 3m,the max measure-ment error is 5.58?m,the standard deviation is 2.20?m.2.Due to the limitations of the traditional coherence detection,such as mechanical scan range and the repetition scan range,an optical sampling measurement method based on FOFC is designed.The method utilizes the fibre noise cancelation technique based on the optoelectronic oscillators?OEO?,and provides a stable long fiber reference arm for the absolute distance measurement system.3.The principle of OEO is analyzed,as well as the oscillation conditons and the oscillation frequency.The models of distance measurement by single loop OEO and dual loop OEO are discussed in details.The experiment of locking the long fibre is designed and performed,which is capable of providing a stable reference arm.Within the 90 minutes locking times,the shift of the long fibre is less than the 10^-10 of the total long fibre length,which satisfies the need of the experiment..