Linewidth Compression of DFB Laser With a High Ratio Based on SIL and PDH

A cost-effective linewidth compressing method for distributed feedback (DFB) laser with a high ratio based on self-injection locking (SIL) and Pound-Drever-Hall (PDH) is proposed. The combination of SIL and PDH helps to reduce the phase noise of the DFB laser, thus a high linewidth compression ratio can be achieved. The experiment results show the single sideband (SSB) phase noise of a commercial DFB laser has been reduced by more than 75-dB in the frequency range from 100-Hz to 10-kHz. The linewidth is narrowed to be around 140-Hz compared with the free-running state of 2.3-MHz, with a high compression ratio of over $1.6\times 10 ^{4}$ . The in-loop Allan deviation (ADEV) of the DFB laser is measured to be $5.4\times 10 ^{-11}$ within the average time of 100 s, indicating the long-term frequency stability.