Wide tunable random fiber laser with sub-kHz narrow linewidth based on disordered fiber Bragg grating array

We demonstrate a wide-tunable random fiber laser (RFL) with narrow linewidth and low noise. The tunable RFL is achieved by combining random feedback from a disordered fiber Bragg grating array (FBGA) with a broad scattering wavelength range and the gain from an erbium-doped fiber (EDF) with a broad amplification wavelength range. The disordered FBGA is fabricated using a femtosecond laser direct writing technique by varying the random distances and grating periods. Multiple scattering of light within the disordered FBGA results in narrow reflection peaks, leading to a reduced linewidth and low noise of the RFL. Such random feedback with a broad scattering wavelength range, uniform scattering strength, and narrow reflection peaks is critical for a wide-tunable random fiber laser with narrow linewidth and flat laser output intensity. Experimental results show that the wavelength of the single-mode RFL is tunable over a range of 35.9 nm with a minimum linewidth of 470 Hz. Furthermore, the power fluctuation for a narrow tunable wavelength range (1 nm) of the FBGA-based RFL is more than 4 times lower than that of the random fiber grating (RFG)-based RFL. Relative intensity noise (RIN) exhibits a level of -110 dB/Hz in the frequency range beyond 100 kHz, which is suppressed by ∼17 dB compared to the RFL with RFG feedback. The wide tunable RFL with sub-kHz narrow linewidth offers a unique setting for telecommunications and sensing.