Ultra Narrow Linewidth Distributed Feedback Fiber Laser Based on Self-injection Locking

We have reported an ultra narrow linewidth fiber laser based on π phase-shift fiber Bragg grating (π-FBG) and self-injection locking, in which the π-FBG is inscribed on Erbium-ytterbium co-doped fiber with scanning phase mask method. Using self-injection locking, the relaxation oscillation frequency (ROF) peak was reduced about 25 dB from -103 dB/Hz to -128 dB/Hz. The 20-dB linewidth of the laser was suppressed to around 500 Hz.