Transfer Of Laser Frequency Stability Based On Optical Frequency Comb

Narrow linewidth laser has important and extensive applications in atomic optical clock,gravitational wave detection,precision spectroscopy,and determination of physical constants.With the development of optical frequency comb,the link between optical frequency and microwave frequency is realized,so that optical frequency can be measured accurately and the optical frequency standard can be established.At the same time,the optical frequency comb spans a very wide spectrum.The optical frequency synthesizer based on the optical frequency comb enables the frequency stability of continuous laser with different optical frequencies to transfer to each other.Starting from the realization of frequency stable narrow linewidth CW laser,the frequency stability of narrow linewidth CW laser is transmitted to microwave frequency and another CW laser by using optical frequency comb.The transmission of frequency stability is studied.Frequency stabilization technology of CW lasers,locking technology of optical frequency combs and mutual locking technology of CW lasers and optical frequency combs are the keys to realize the above frequency chains.Therefore,the locking technology used in this paper is also theoretically analyzed and experimentally validated.The main research contents and achievements are as follows:1.We used PDH frequency stabilization technology to lock a 972 nm semiconductor laser to high precision Fabry-Perot cavity.The precision of Fabry-Perot cavity is 2086000,which can support narrow line-width output of CW laser in Hertz order.The locked972-nm CW laser can be stabilized for tens of days,which provides a guarantee for subsequent experiments.2.Locking Yb-doped optical frequency comb into microwave frequency reference source and optical frequency reference source respectively.The carrier envelope phase-shifted frequency signal of optical frequency comb is obtained by constructing f-2f interference system.The pump current of optical frequency comb is controlled by feedback of phase-locked loop circuit,and the carrier envelope phase-shifted frequency is locked.After locking,the frequency stability can reach 2.36×10^-17/s.There are two ways of repetitive frequency locking of optical frequency comb,i.e.locking to RF reference source and optical frequency reference source respectively.The repetition frequency is locked into the RF reference source by the piezoelectric ceramics of the fiber optic oscillator which is controlled by the circuit feedback directly.The frequency stability of the locked repetition frequency signal is 4.6×10^-14/s.To lock the optical frequency comb onto the optical frequency reference source,beat signals of the comb in the optical frequency comb domain and the optical frequency reference source need to be obtained.In this experiment,the selected optical frequency reference is a 972-nm narrow-linewidth CW laser stabilized by PDH technology to high-precision Fabry-Perot cavity.The supercontinuum spectrum covering 972 nm is obtained by amplifying and supercontinuum generation of Yb-doped fiber optical frequency comb.The beat frequency of 972 nm narrow linewidth CW laser is obtained,and the beat signal with signal-to-noise ratio of 40 dB is obtained.The piezoelectric ceramics and EOM of the fiber optic oscillator are feedback controlled by the phase-locked loop circuit,and the optical beat signal is locked,that is,the optical frequency comb is locked to 972 nm optical frequency reference source.The relative frequency stability of the locked optical frequency comb is 2.4×10^-18/s,the relative linewidth is 0.91 mHz,and the integrated phase noise of 1Hz-10MHz is 360 mard.The optical frequency comb stabilizes to the optical frequency reference source,which provides the basis for the subsequent coherent transmission experiment of optical frequency stability.3.The frequency stability and narrow linewidth of 972 nm CW laser are transferred to 1064 nm CW laser by locking a 1064 nm CW laser onto the Yb-doped fiber optical frequency comb.In order to solve the complex problem of phase-locked loop?PLL?technology in the process of CW laser to optical frequency comb locking,the pre-feedback locking technology is adopted to achieve 280 kHz wide bandwidth locking.Compared with the 1064nm CW laser before and after lock-in,the relative linewidth is narrowed by 1.14mHz from kHz magnitude,and the frequency stability is increased by three orders of magnitude from 2.4×10^-14/s before lock-in to 1.5×10^-17/s after lock-in.The measured integrated phase noise from 1Hz to 10MHz is 381 mrad,and the integrated phase noise from 1mHz to 10Hz is only 20.5mrad.This locking technique for optical frequency stability transfer and stable light source can play an important role in optical frequency synthesis and gravitational wave detection experiments.