| Fast,real-time,and high-precision distance measurement is a key technology in the fields of satellite formation flying,large-scale equipment manufacturing,and gravitational wave detection.Femtosecond optical frequency comb has the characteristics of ultra-wide spectral range,ultra-narrow pulse width and ultra-stable pulse sequence interval.It can not only use periodic pulses of the time domain to achieve large-scale time-of-flight ranging,but also use the coherence spectrum of the frequency domain.The line obtains high-precision interference information,which can give full play to its advantages in the field of large-scale,high-precision absolute distance measurement.Among the many ranging technology routes that use optical frequency combs as light sources,the dual-comb ranging method uses a pair of phase-locked combs with a small repetition frequency difference as signal light and local light,through asynchronous optical sampling,the cross-correlation interferogram between the two optical combs is presented at radio frequency,without any mechanical or electronic scanning device to artificially adjust the pulse alignment between the signal light and the local light to quickly achieve a large measurement range and high-precision distance measurement.Therefore,the dual-comb ranging method has become a research hotspot at domestic and foreign in the past decade.The target distance measured by the dual-comb ranging method is actually the optical path difference between the signal light and the reference light.When applied to free space,the unique wide-spectrum characteristics of the optical comb will inevitably make the measurement results be affected by the atmospheric environment;at the same time,it is also closely related to the system parameters.This thesis focuses on this problem.First,it presents the theoretical model of dual optical comb ranging;secondly,it analyzes the relationship between the measured target distance and system parameters and atmospheric environmental factors,and artificially adds different types of noise(time,frequency,phase,etc.)To simulate the noise in actual measurement,and correct the measurement results through subsequent software signal processing;finally,a set of dual optical comb experimental demonstration system was established to verify the system’s ranging ability.The main research content of this paper is divided into the following parts:1)The theoretical basis of the dual optical comb ranging system is studied.This part firstly gives the theoretical model of the optical frequency comb from the perspective of the time domain and the frequency domain,and proves that the two satisfy the Fourier transform relationship and are equivalent;secondly,it discusses the principle of dual optical comb asynchronous optical sampling in detail.The relationship between the measurement results of the dual optical comb,the setting of system parameters and the elements of the atmospheric environment is deduced;finally,the principle of the software noise correction technology is explained.2)A detailed simulation of the dual optical comb ranging system is carried out.This part uses Matlab numerical simulation to analyze the influence of system parameters and atmospheric environment factors on the system measurement results.System parameters include repetition frequency,repetition frequency difference,repetition frequency difference jitter,bandwidth,spectral shape within bandwidth,relative line width between two optical combs,carrier envelope frequency shift jitter;atmospheric environment factors include temperature,humidity,and atmospheric pressure.The simulation results show that: as the repetition frequency increases,the effect of repetition jitter on the ranging results will decrease;the smaller the repetition frequency difference between the local light(LO)and the signal light(SIG),the longer the period of the radio frequency interferogram,the finer the interferogram,which is more conducive to the extraction of the peak position,thereby improving the ranging precision;the increase of the optical bandpass filter(BPF)bandwidth has little effect on the ranging precision;the spectral shape within the BPF bandwidth has little effect on the measurement precision;with the increase of the relative line width between the two optical combs,the ranging precision gradually decreases;the carrier envelope frequency shift has a influence on the shape of the RF interferogram,but after envelope fitting,it has little influence on the target optical path drift;the influence of atmospheric environment temperature jitter on the measurement distance is1μm/(m? ℃);the influence of atmospheric pressure jitter on the measurement distance is 2.6μm/(m?k Pa);the influence of atmospheric humidity on the distance measurement is small.In addition,the error correction algorithm is used to correct the artificially added time,frequency,and phase noise;after correction,the system’s ranging precision has been improved by 2×105 times.3)Carried out the experiment of dual optical comb ranging system.Using two free-running optical combs with a difference in repetition frequency,a set of dual optical comb ranging experiment verification system was established,and the parameter settings of the experimental device were introduced in detail.When the dual optical comb is running freely and the repetition frequency difference jitter is in the range of about 10 Hz,the distance measurement precision obtained is in the order of 10 microns;the paper analyzes the experimental results in detail.The research work of this paper ranges from theoretical analysis,to simulation,and finally to experimental verification.Theoretically,the factors affecting the measurement results of the dual optical comb ranging system have been fully grasped,and the ranging capability of the dual optical comb ranging system has been verified experimentally.The research conclusions and research methods obtained in the thesis have laid a certain foundation for the dual optical comb experimental system to go out of the laboratory and into practical application. |
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