Research On Precision Length Measurement Technology Using On-chip Microresonator Based Soliton Microcomb

Optical frequency comb,as a revolutionary light source with discrete and equally-spaced frequency modes,has gradually become the cornerstone of many fields.Thanks to the ultra-small size and energy enhancement effect of microresonator,the ultrahigh-repetition-frequency soliton microcomb(SMC)with smooth coherent spectrum emerges,showing its unique advantages and application potential.Length measurement is one of the most basic and universal measurements,and accurate measurement and traceability of length measurements play a vital role in scientific research and industrial production.In this paper,the application of SMC in precision length measurement is studied by combining the SMC with dispersive interferometry(DPI)and fiber Bragg grating(FBG).The main work and innovation points of this paper are summarized as follows.The generation technology of optical frequency comb and precision length measurement technology are reviewed.The sensing principle,demodulation methods and peak tracking algorithms of FBG sensors are summarized too.The principle and main parameters of SMC based DPI are detailed analyzed and the main problems such as long dead zone and low resolution are pointed out.An improved DPI data processing method aimed to eliminate the dead-zone and improve the resolution based on spectral reconstruction and peak position fitting is proposed which has the advantages of small computation and strong adaptability.The characteristics and key parameters of the optical microresonator are studied and based on the LLE equation,the generation theory of SMC in microresonator is analyzed.A high-index doped silica glass(hydex)with high Q value is fabricated and standardized butterfly encapsulated,based on which a SMC with high repetition frequency is generated definitively using an auxiliary optical heating scheme.A high-speed peak tracking algorithm based on SMC for sparse FBG reflectance spectrum(FPTM-ss)is proposed where all matrix operations are eliminated successfully by decomposinging the Moore-Penrose matrix.The common nonlinear errors in FBG interrogation field is analyzed and compensated,and the interrogation speed can be improved by more than 10 times using the FPTM-ss without sacrificing the interrogation accuracy.An interrogation system based on FPGA was designed and developed.At the interrogation speed of 16 k Hz,the accuracy is better than 0.1pm,and the measurement resolution is better than 1pm.An ultra-fast FBG interrogation method based on SMC(SMC-Based-UFI)is proposed which avoids the time-consuming process of spectral acquisition and peak finding fitting,and directly calculated the central wavelength according to the FBG spectral characteristics,thus has a very fast demodulation speed and is suitable for multiplexing system.The key parameters,time efficiency,error and other parameters of the method are analyzed,and the experimental verification is carried out too.Under the interrogation speed of 91 k Hz,the interrogation precision is better than 2pm,and the waveform of high frequency vibration(10k Hz)was well reconstructed.Based on the developed SMC light source and the proposed improved DPI signal processing method,a SMC-DPI based precision ranging system is designed,and the SMC-DPI combined with the phase-modulated laser ranging is used to realize the long-distance,high-speed,real-time measurement with kilometer magnitude and nanometer accuracy.The ranging system is instrumented and designed,and the multi-scene ranging experiment research of SMC ranging system is carried out at super clean laboratory,80 m underground marble guide rail and 1200 m outdoor baseline field scene respectively,where static and dynamic distance are measured.On the ultraclean environment,measurement error is less than 1 microns within 80 m.At1179 m outside,the measurement standard deviation is 5.9μm,the minimum Allan variance is 5.6μm@0.2ms,and the minimum Allan variance is 27nm@1.8s after high-pass filtering.Besides,the high frequency vibration signal with a range of tens of microns is accurately measured.Finally,the error source in length measurement is analyzed systematically,and the uncertainty analysis report is given.