Random spaced index modulation for a narrow linewidth tunable fiber laser with low intensity noise

A tunable random feedback fiber laser with low intensity noise is proposed and experimentally demonstrated. The random feedback is effectively achieved by multiple reflections from 100 randomly spaced refractive index modulation regions over 10 cm SMF in both longitudinal and transverse directions. A tunable erbium-doped fiber ring laser with narrow linewidth of 2.4 kHz and a high side-mode suppression ratio of 59 dB is achieved over a 0.5 nm tuning range. The proposed fiber laser exhibits low relative intensity noise (<-120  dB/Hz) and low frequency fluctuation of ∼3.41×10(-11) over 5 s.