Reduced relative intensity noise of a coherently combined single-mode semiconductor laser array under injection locking

A scheme for reducing the relative intensity noise (RIN) of laser source by an injection locked single-mode semiconductor laser array is proposed and demonstrated. Intensity and phase noise of the slave laser under injection locking are first analyzed by rate equations, and the RIN of the injection locked laser array after coherent combining is then estimated. The RIN of the injection-locked $N$-element laser array can be reduced by a factor about $1/N$ over the entire frequency range in the ideal case. Measurements with a two-element distributed feedback laser array confirm the main theoretical predictions and a nearly 3 dB reduction in RIN is obtained. The effect of the key parameters on the RIN of the injection locked array is investigated as well.