High SNR Watt-Level Single Frequency Yb-Doped Fiber Laser Based on a Saturable Absorber Filter in a Cladding-Pumped Ring Cavity

Abstract

A single frequency ring fiber laser is reported based on a cladding-pumped ytterbium-doped fiber (YDF). A medium concentration polarization maintaining (PM) YDF is utilized in ring cavity as a saturable absorber that acts as an ultranarrow bandwidth filter. Here, by making use of double-clad and PM fibers in the cavity configuration, thermal noises are notably damped and the frequency instability is minimized due to the temperature fluctuation and polarization variation. The laser yields up to 35 mW of a stable single longitudinal mode output at 1079.68 nm, whereas the corresponding linewidth is estimated less than 6 kHz. Subsequently, a fiber amplifier is employed to boost up power to 5.21 W with the slope efficiency of 45.6%. The amplifier steadily operates below the stimulated Brillouin scattering threshold power. The signal-to-noise ratio is measured to be higher than 70 dB, while the laser linewidth remains unchanged. The relative intensity noise of the laser at the relaxation oscillation frequency of 173 kHz is determined to be −115 dB/Hz, which approaches to −134 dB/Hz at frequencies over 500 kHz.