Study Of Multi-wavelength Single Frequency Yb³⁺-doped Fiber Laser

The Abstract Part consists of both the Chinese abstract and the English abstract.The Chinese abstract should have the length of approximately 500 Chinese characters for a master thesis and 1000 for a Ph.D.dissertation.The single-frequency(S-F)fiber laser is just existed one longitudinal-mode oscillation in the resonant cavity and has a narrow linewidth,low noise,tunable wavelength,high stability,and good coherence.In recent years,it has been widely used in optical fiber sensing,optical fiber communication,laser ranging and other fields etc,so the research of S-F fiber laser is a hot topic at home and abroad.In this paper,we demonstrate a switchable dual-wavelength and a wavelength-tunable S-F fiber lasers.The resonant cavity structure is designed for 1?m band S-F output,and the corresponding filter is proposed to eliminate the multi-longitudinal mode.Then,a stable S-F narrow linewidth and low noise fiber laser output is obtained.The main works aer as follows:1.We analyzed the critical technology for the resonant cavity structure and filter for S-F fiber lasers,and analyzed the energy structure,rate equations and spectral characteristics of Yb3+-ions in the gain fiber,and established the theoretical model of the ring resonator fiber laser.Then,we introduced the measurement method of the S-F signal based on the scanning F-P etalon and the linewidth based on the delay-shifting self-heterodyne method.2.In order to achieve a stable dual-wavelength narrow-linewidth low-noise fiber laser output,we use a geometric “8”-shaped resonant cavity structure combined with a non-linear amplifying fiber ring mirror to select longitudinal mode and achieve a stable switchable dual-wavelength S-F fiber laser outputs at 1064.65 and 1065.45 nm.Meanwhile,the linewidth of the fiber laser for each wavelength is approximate 17.07 k Hz and 18.64 k Hz with a 20 d B linewidth,which means the laser linewidth is approximate 853 Hz and932 Hz FWHM.Correspondingly,the measured relative intensity noise(RIN)is less than120 d B/Hz at frequencies over 5.0 MHz.Moreover,we also analyzed its characteristics such as output power and spectrum.3.The S-F laser output with a tuning range of 1020-1090 nm is achieved by using multiple fiber ring structure composite cavity and fiber ring filter,and the output signal optical signal-to-noise ratio is higher than 50 d B.When the output frequency is 1064 nmsingle frequency,the 35 km single mode fiber is used as the delay line.The 20 d B linewidth measured by the 1064 nm single frequency laser is approximate 2.32 k Hz and the output wavelength fluctuation is less than 1%.