NONLINEAR INJECTION LOCKING DYNAMICS AND THE ONSET OF COHERENCE COLLAPSE IN EXTERNAL CAVITY LASERS

We present a theoretical analysis of the experimentally observed collapse of coherence in semiconductor lasers exposed to moderate optical feedback. A main point in the analysis is, that coherence collapse in the delayed-feedback system shows up as bistability in a much simpler model which corresponds to an injection locking system. Based on this, we derive a simple analytical expression, valid for DFB as well as Fabry-Perot lasers, for the critical feedback level at which coherence collapse sets in. Simulations of the nonlinear injection locking model reveal the presence of complicated nonlinear dynamics with period-doubling bifurcations and coexisting attractors even inside what is normally denoted the stable locking range. © 1990 IEEE