Research On High-precision And Wide-tuning Technology Of Er³⁺-doped Single-frequency Fiber Laser

The tunable single-frequency Er³⁺-doped fiber laser has the characteristics of wide tuning range,high optical signal-to-noise ratio,narrow linewidth,low noise and good compatibility.It has important applications in the fields of spectroscopy,optical detection,optical sensing,and optical fiber communication.However,in terms of optical fiber communication technology based on dense wavelength division multiplexing technology,with the continuous growth of communication traffic,the demand for the number of channels has greatly increased,which puts forward higher requirements on the tuning accuracy and tuning range of the laser signal.However,limited by the gain unevenness of the Er³⁺-doped silica fiber and the low emission cross section of L-band,as well as the appearance of mode hopping and multi-mode competition,it is difficult to achieve high-precision and wide-tuning single-frequency fiber laser output.Based on the working principles of different tuning technologies and filtering technologies,this thesis has carries out the research on high-precision and wide-tuning technologies of the single-frequency fiber laser.The specific contents are as follows:1.Several wavelength tuning techniques and filtering techniques used in the fiber lasers are introduced.The tuning methods are respectively Sagnac loop,single-mode-multimode-single-mode structure filter,tunable fiber grating and Fabry-Pérot tunable filter.The feasibility of Sagnac loop and single-mode-multimode-single-mode structure filter as tunable devices is investigated experimentally.The filtering methods are respectively compound cavity,tracking filter,chirped fiber grating Fabry-Pérot cavity and dynamic grating.The feasibility of the tracking filter as a filter device is theoretically analyzed and experimentally explored.The review and experimental exploration of the tuning and filtering techniques can provide guidance and reference for subsequent experimental research.2.It is proposed to use the chirped fiber grating Fabry-Pérot cavity as the filter device and the uniform fiber Bragg grating（UFBG）as the tuning device to realize the C-band high-precision tunable single-frequency fiber laser output.The filtering effect of the chirped fiber grating Fabry-Pérot cavity is simulated and analyzed,and the filtering principle of the single-frequency fiber laser is analyzed.A controllable tensile stress is applied to the axial direction of the UFBG through a stress structure,and the polarization state of the chirped fiber grating Fabry-Pérot cavity is controlled by a polarization controller.The single-frequency fiber laser output with the tuning wavelength range of 1550.28-1560.40 nm,the tuning accuracy of less than 54 pm,the optical signal-to-noise ratio of 71 dB and linewidth of less than 630 Hz is achieved.In the entire tuning range,the relaxation oscillation appears at 62kHz with an intensity of-108 dB/Hz.In the frequency band from 0.4 to 7.5 MHz,the relative intensity noise is less than-149 dB/Hz.3.It is proposed that a fiber Fabry-Pérot interferometer and a dynamic grating based on a1.6-m-long un-pumped Er³⁺-doped fiber form a longitudinal mode selection device,combined with a fiber Fabry-Pérot tunable filter as a tuning device,to achieve a C+L band wide-tuning single-frequency fiber laser output.Based on the mode selectivity and 3 dB bandwidth of the Fabry-Pérot tunable filter,fiber Fabry-Pérot interferometer and dynamic grating,the filtering principle of the single-frequency fiber laser is analyzed.By changing the control voltage of the piezoelectric ceramic load in the Fabry-Pérot tunable filter,a tunable single-frequency fiber laser output with a tuning wavelength range of 1535.50-1612.19 nm,a tuning bandwidth of 76.69 nm,a tuning accuracy of 0.2 nm,and a linewidth of less than 310 Hz is achieved.In the entire tuning range,the relative intensity noise is less than-143 dB/Hz in the frequency band above 1 MHz...