Microwave signals generated by optical heterodyne between injection-locked semiconductor lasers

Single-mode-laser rate equations with added Langevin noise sources are used to study injection-locked semiconductor lasers. Two slave lasers are frequency-locked on the same or different sidebands of a current-modulated master laser. The optical heterodyne between the two secondary lasers is characterized. It is demonstrated that the frequency stability of the source modulating the master laser is preserved on the sidebands and partially transferred to the slaves. A linear model is first investigated. Static operation conditions and small-signal behavior are then calculated. Direct simulation of the rate equations for each laser is next achieved. This highlights the validity domain and limitations of the linear model. A more complete set of results-such as laser and heterodyne spectra-is also obtained. It is moreover shown that synchronization of the slave laser diodes by optical injection-locking leads to strongly correlated, while not identical, laser fields. Finally, simulation results are compared to experimental data.