Semiconductor laser locked by external radiation

Injection locking of a semiconductor laser by external radiation is investigated. Equations describing a locked laser are derived and solved allowing for emission of spontaneous radiation and excitation of stray modes. An analysis is made of the stability of steady-state solutions. It is shown that incorrect results are obtained if a locked laser is analyzed in a single-mode approximation and spontaneous emission is ignored in the case of positive frequency detuning. Inclusion of stray modes reduces permissible values of the phase shift between the injected and own laser radiation, and gives rise to an asymmetry of the dependence of the phase shift on the detuning. The dependence of the output power on the injected power is used to find the spontaneous emission factor. Experiments are reported in which the output power sometimes exhibits fluctuations in the locked state.