High-power, High Signal-to-noise Ratio Single-frequency Brillouin Fiber Laser

High optical signal-to-noise ratio(OSNR) single-frequency fiber lasers with high output power are of huge interest because of their potential applications, such as optical communications, high-precision sensing, coherent detection, laser LIDAR and so on. In recent years, the output power of the single-frequency fiber lasers have been greatly promoted, but it is difficult to preserve high OSNR. The Brillouin fiber laser(BFL) can realize high OSNR single-longitudinal-mode(SLM) laser output owing to the narrow gain bandwidth of the stimulated Brillouin scattering(SBS), the noise suppression and linewidth narrowing for the pump laser. Based on the above reasons, high-power, high OSNR BFLs are studied theoretically and experimentally in an all-round way in this thesis. The main contents are as follows:1. The theory for the SLM generation and measurement of the fiber laser has been described in this dissertation. Firstly, the basic principle for longitudinal mode selection has been described. Then, to better comprehend the longitudinal mode characteristics of the single-frequency fiber laser, we introduce the different methods of longitudinal mode selection and measurement detailedly, which can lay the foundation for the research of the single-frequency BFL.2. The basic principle of the single-frequency BFL has been explored in this dissertation. According to the SBS in the fiber, we elaborate the Brillouin gain spectrum of the optical fiber, the Brillouin threshold and output linewidth of the single-frequency BFL.3. The distributed Bragg reflector(DBR) single frequency fiber laser used the home-made FBG as the cavity mirror has been demonstrated. The FBG is written in the photosensitive fibers and hydrogenated fibers successfully with phase mask technique in the laboratory, and the good performance of the FBG enables it suit to DBR single frequency fiber laser. The DBR single frequency fiber laser is amplified by one-stage Yb-doped all-fiber amplifier, and generates a maximum output power of 10.33 W with the OSNR of 50 d B. The high-power single-frequency fiber laser can be used as the pump system of the single-frequency BFL.4. A high-power, high OSNR single-frequency BFL has been demonstrated. The high-power single-frequency laser is used to pump the Brillouin ring cavity, and the launched pump power of Brillouin ring cavity is only 2.15 W limited by the damage threshold of the optical isolator. By optimizing the length of the Brillouin ring cavity to 10 m, the BFL generates a maximum output power of 1.4 W with the OSNR of 77 d B and a linewidth of 3 k Hz.