Simulation, Design, and Implementation of a Narrow Linewidth Ytterbium Fiber MOPA System at 1087 nm

Abstract: This thesis focuses on simulating, designing, and characterizing a narrow-linewidth continuous-wave (CW) Ytterbium (Yb) master oscillator fiber amplifier (MOFA) system. The primary goal was to achieve a watt-level output at 1087 nm with a narrow 1 GHz linewidth, making the MOFA well-suited for serving as a pump source in Terahertz (THz) generation experiments. This system can essentially be divided into two main parts: a narrow-linewidth Yb fiber seed laser (master oscillator), responsible for delivering a stable and narrow-linewidth signal power, and a Yb fiber amplifier for scaling this signal power.The all-fiber Yb seed laser produced a maximum output power of 11.31 mW at 1087.39 nm with a narrow linewidth of approximately 1.86 GHz. The narrow-linewidth operation was achieved by incorporating a fiber Bragg grating (FBG) as a resonator mirror and an intracavity FBG based Fabry-Perot interferometer as a bandpass filter, allowing only specific portion of the FBG reflected spectrum to pass through. A simulation was subsequently developed to identify the optimal Yb gain fiber lengths and pump powers required to realize an efficient Yb fiber amplifier with high gains. Finally, by employing a 10-meter Yb fiber amplifier, seed laser’s output power was boosted to 0.86 W, resulting in a 23.1 dB gain, achieved with a notable power conversion efficiency of 33 %. The final amplified spectrum exhibited a Gaussian-like profile centered at 1087.12 nm, with a bandwidth of less than 12.7 GHz. By further scaling the output power to watt-level range, this Yb MOFA system has the potential to be utilized as a pump source in Terahertz (THz) generation research.