Quantum noise of laser diodes

Single-mode laser theory for semiconductor lasers predicts sub-Poissonian light generation for a laser quietly driven far above threshold. Experiments have shown however that only few laser diodes exhibits such reduced intensity noise. We present a review of different mechanisms that have been proposed to explain the excess noise observed in semiconductor lasers, including imperfect anticorrelations in multimode lasers, and Petermann excess noise factor in single-mode lasers.