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 1 cm 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 2.1 kHz with 58 dB side-mode-suppression-ratio. The frequency noise is ∼1 Hz/Hz1/2 above 1 kHz, and the frequency jitter is ∼1.8 × 10−12 over 100 s.