Gain-dynamics-dependent noise evolution in a narrow-linewidth single-frequency Yb-fiber amplifier chain

The relative intensity noise (RIN) and frequency noise (FN) of a single-frequency fiber laser (SFFL) are essential parameters that directly determine the sensitivity of high-precision optical metrology. Here, we report the gain-dynamics-dependent evolution of the RIN and FN in an SFFL Yb-fiber amplifier chain. Three types of single-mode Yb-doped fibers constructed with diverse mode-field diameters (MFD), core diameter, overlapping factor and doping concentrations were separately employed to achieve three SFFL amplifiers. The noise characteristics of the SFFL during the fiber amplification processes were investigated using contrast measurement curves of the RIN and FN. These results indicate that the amplifier-induced RIN and FN exhibit an iconic corner frequency of approximately 10 kHz. The relationships between the noise and signal input power exhibit opposite trends in the low- and high-frequency regions. In particular, the RIN curves of the noise power spectral density (PSD) reveal that a gain fiber with a larger overlapping factor can optimize the RIN. Moreover, higher doping concentration gain fiber can suppress the FN of the low-frequency region, realizing a narrower-linewidth SFFL. We believe that this study provides significant guidance for optimizing high-power, low-noise SFFL generation.