Narrow linewidth low frequency noise Er-doped fiber ring laser based on femtosecond laser induced random feedback

Abstract

We propose and demonstrate a narrow linewidth, low frequency noise Er-doped fiber ring laser with resonant feedback in a femtosecond laser induced random medium of deep refractive index modulation in three dimensions. Eight concatenated single-mode fiber segments about 1cm long, each carry a total of 8×500 randomly spaced laser-written-planes. Numerous low-finesse spectral filters are formed to significantly suppress sub-cavity modes, ensuring single-mode operation within a wavelength-locking range. The linewidth of the laser is 2.1kHz with 58dB side-mode-suppression-ratio. The frequency noise is ∼1Hz/Hz1/2above 1kHz, and the frequency jitter is ∼1.8×10-12over 100s.