Subkilohertz linewidth reduction of a DFB diode laser using self-injection locking with a fiber Bragg grating Fabry-Perot cavity.

A simple and low-cost 1550 nm semiconductor laser with subkilohertz intrinsic linewidth is experimentally demonstrated. A commercial distributed feedback diode laser is self-injection locked to the resonance transmission peaks of a fiber Bragg grating Fabry-Perot cavity through a polarization-maintaining fiber ring with the optical path length of 4 m, with the laser frequency noise suppressed by over 70 dB in the Fourier frequency band from 5 Hz and 1 kHz. The laser features an intrinsic Lorentzian linewidth of 125 Hz as well as a relative intensity noise of <-142 dBc/Hz above 2 MHz, and provides over 0.8 nm quasi-continuous tunability, which is suitable for advanced applications requiring a narrow linewidth laser with ultralow frequency noise.