| "Tianqin Project"is a Chinese gravitational wave detection project,whose goal is to listen to the sound of the universe.The demand indices of the laser source in this gravitational wave detection p lan is:the 1064 nm continuous-wave laser power emitted from the spacecraft should reach 4 W,and the optical power stability should be lower than 10-3/Hz1/2@1 m Hz-1 Hz,so we need to develop a laser source that meets the technical requiremant independently.In order to obtain high-power,high-quality and high-stability continuous laser,after the preliminary investigation,we decide to adopt Ytterbium-doped all-fiber power amplification sche me based on the main oscillation power amplification（MOPA）structure to amplify the linearly polarized signal optical power at 1064 nm,and use digital PID lock module to stabilize the optical power of the amplified signal optical.This thesis is mainly composed of the following two parts:1.From the aspect of the level structure and spectral characteristics of Ytterbium ions,the reasons for choosing high concentration Ytterbium ion-doped fibers as gain media are briefly explained.By theoretical analyzing the amplification process of the Ytterbium-doped fiber amplifier,the rate equation of the double-clad fiber amplifier is established.After that,two concepts of amplifier gain and pump threshold are introduced,and the optimal length and corresponding gain of doped fiber in the amplifier are also derived.Based on the above theoretical model,in order to optimize the performance of the amplifier,the thesis uses the open source program to simulate the output characteristic curve of the fiber amplifier during normal operation when the parameters such as the seed optical power,pump optical power,ytterbium-doped fiber（thorium particle doping concentration,core radius,etc.）and pumping method are determined.2.In order to effectively reduce the amplified spontaneous emission（ASE）component in the amplifier and improve the signal-to-noise ratio（SNR）of the output optical signal,we build a full-fiber front-end pumped ytterbium-doped fiber amplifier with filter in the system.This MOPA system composed of a two-stage amplification,uses a commercial laser from RIO to generate a 1064 nm continuous-wave laser.In the pre-amplification system,a single-mode pump diode（610.30 m W,976 nm）is applied to pump the ytterbium-doped fiber.The average output power is 157.21 m W,and the optical-to-optical conversion efficiency is 25.76%.While in the power amplification system,we use a multimode laser diode（8.225 W,976 nm）as the pump source and obtain a linearly polarized continuous-wave single laser with an average output power of4.101 W,a polarization extinction ratio of 31.2 d B,and an optical-to-optical conversion efficiency of 49.86%.Subsequently,we theoretically analyze the effect of stimulated Brillouin scattering（SBS）in the fiber amplifier,and set up an experimental device for testing SBS,the experimental results show that during the operation of the amplifier no obvious stimulated Brillouin scattering phenomenon is found.After verifying that the built amplifier can work normally,we use a digital PID feedback module to control the current of pump diodes of pre-amplifier and power amplifier to actively suppress the optical power fluctuation.The experimental results show that after power noise suppression,the amplifier can stably output a 1064 nm linearly polarized laser with an average power of 4.073 W,and the relative intensity noise of the signal output power reaches a level better than 10-3/Hz1/2 at 1 m Hz-1 Hz. |
