Experimental Investigation on Spectral Linewidth and Relative Intensity Noise of High-Power Single-Frequency Polarization-Maintained Thulium-Doped Fiber Amplifier

We investigate the spectral linewidth and relative intensity noise (RIN) of an all-fiber single-frequency polarization-maintained master oscillator and power amplifier at 1925 nm. It is found that the linewidth of the fiber amplifier is related to the power ratio of signal laser to accumulated amplified stimulated emission noises. A 3-dB linewidth of 56 kHz is measured at a maximum output power of 45 W, resulting to a linewidth broadening of 20 kHz compared to the 36-kHz linewidth of the seed laser. The RINs of the preamplifier and the power amplifier are measured to be -108 and -90 dBm/Hz at the relaxation frequency, respectively.