Coherently Combined DFB Laser Array Chip With Reduced Relative Intensity Noise

The relative intensity noise (RIN) behavior of coherently combined DFB laser array by injection locking is experimentally investigated. A monolithically integrated four-element DFB laser array with a splitter and an output coupler is fabricated, and the frequency stabilities of the DFB lasers are improved to ensure a stable injection locking of DFB laser array by a master laser. It is demonstrated that the RIN of the coherently combined laser array is reduced by almost 20 dB at low frequencies compared with the free-running state. The results indicate that monolithic integration of DFB laser array under injection locking can help improve the RIN performance by eliminating variation in coupling delays and phase jitters.