53-dB phase noise suppression and Hz-range linewidth emission in compact Brillouin/erbium fiber laser

We demonstrate 53-dB phase noise reduction in a compact Brillouin/erbium fiber laser (BEFL), which uses 4-m erbium-doped-fiber (EDF) providing both the Brillouin gain and linear gain. A 360-kHz-linewidth laser diode is used as the Brillouin pump (BP) and excites the Brillouin Stokes light. The linewidth of the BEFL is estimated 1.8-Hz based on the correlation between the linewidth and phase noise. Experimental result demonstrates 6-Hz linewidth by beating the emission of two compact BEFLs. This fiber laser provides a simple and effective method to reduce laser phase noise and realize ultra-narrow-linewidth light. It presents many applications in such as interferometric fiber sensing, coherent optical communications, optical clocks, and precise spectroscopy.