140-Hz Narrow-Linewidth Brillouin/Erbium- Ytterbium Fiber Laser

We demonstrate an ultra-narrow-linewidth Brillouin/Erbium-Ytterbium co-doped fiber ring laser, which uses a length of 80-cm Erbium-Ytterbium co-doped fiber as both the Brillouin gain and linear gain media. The 976-nm pump threshold is only 80 mW when the Brillouin pump power is 20 mW. The output power of this laser reaches about 200 mW. The laser linewidth is as narrow as 140 Hz. The relative intensity noise of the fiber laser is −145 dB/Hz. The phase noise at 1 kHz is as low as to −107 dB re rad/Hz1/2 (1-m optical path difference). Moreover, the 140-Hz-linewidth Brillouin laser light is transferred from a 2-MHz-linewidth Brillouin pump light. This fiber laser presents outstanding linewidth-narrowing characteristic. It presents many potential applications in coherent communications, optical fiber sensors, and etc.