Er-doped-fiber-based Optical Frequency Comb:Application To Optical Frequency Measurement

Optical frequency combs has been deeply studied due to its important applications in optical frequency measurement,optical frequency standard,low noise microwave signal generation,astronomical observation,nonlinear optics,basic physical constant measurement and theoretical verification.Compared with other femtosecond optical combs,the erbium-doped fiber femtosecond optical comb has many advantages such as various types of components,low price,easy design of all-fiber structure,compatibility of working wavelength and optical communication band,and has become a hot research and application.In this paper,we study the key technologies of femtosecond mode-locked lasers,stabilize the comb's frequencies,and explore the application of low-noise,high-reliability application-type erbium-doped fiber femtosecond optical comb technology.The important research content and innovative achievements are as follows:In terms of femtosecond laser,the experimental schemes of the Er-doped fiber femtosecond lasers based on nonlinear polarization rotation?NPR?and semiconductor saturation absorber?SESAM?mechanisms are studied.The characteristics of the two lasers are analyzed,such as the noise level and the systems'environmental sensitivity.The advantages of both femtosecond lasers are discussed.In order to solve the problem of high reliability and low noise of laser based on single mode-locked mechanism,we propose an experimental scheme combining NPR and nonlinear amplifier loop mirror?NALM?.The experimental results show that the noise level of the laser is -130 dBc/Hz@1Hz and -144 dBc/Hz@100 Hz,which is the best fiber laser as we all know.At the same time,the laser has the advantages of large mode-locking margin,self-opening locking and high power conversion rate.In terms of frequency generation and control of the combs,We study the frequency generation and control of two femtosecond optical comb systems based on the NPR mode-locking technology and the hybrid mode-locking technology.The phase noise levels of the two types of femtosecond combs are measured,and the phase jitters of the two systems are less than 1 rad.In order to realize wide range and high bandwidth frequency control of optical frequency comb using single frequency control modulator,the experimental scheme of laser polarization rotation control femtosecond optical comb frequency is proposed.Compared with the traditional frequency control method,the method uses the whole optical birefringence cavity of femtosecond laser.We use the designed electro-optical polarization modulator?EOPM?to control the f_ceo and f_rep with a bandwidth of 1.8mHz.The sensitivity of f_r to the electric field intensity applied to the EOM is about 100 times larger.In terms of optical frequency measurement using optical comb,the principle of measuring optical frequency with femtosecond light comb is analyzed.The requirement of frequency measurement of strontium optical clock using erbium-doped fiber optical comb is discussed.The experimental scheme of amplification and frequency multiplication was used for the first time.By adjusting the nonlinear optical fiber parameters and amplification power,the single mode energy at the corresponding frequency of the strontium light clock's working laser can be adjusted as high as possible.The single mode energy of the comb tooth obtained at 698.5nm and 707nm is 1mm and 0.7mm respectively.The signal-to-noise ratio?SNR?of the beat frequency signal between the single frequency laser and femtosecond light comb frequency of 698.5nm is up to 40 dB,10 dB higher than the input SNR of subsequent frequency counting devices,improving the robustness of frequency lock.