Analysis of an Optically Injected Semiconductor Laser for Microwave Generation

The nonlinear dynamical period-one oscillation of an optically injected semiconductor laser is investigated analytically. The oscillation is commonly observed when the injection is moderately strong and positively detuned from the Hopf bifurcation boundary. The laser emits continuous-wave optical signal with periodic intensity oscillation. Since the oscillation frequency is widely tunable beyond the relaxation oscillation frequency, the system can be regarded as a high-speed photonic microwave source. In this paper, analytical solution of the oscillation is presented for the first time. By applying a two-wavelength approximation to the rate equations, we obtain mathematical expressions that characterize the oscillation. The analysis explains the physical origin of the periodic intensity oscillation as the beating between two wavelengths, namely, the injected wavelength and the cavity resonance wavelength. As the injection strength increases, the optical gain reduces, the cavity is red-shifted through the antiguidance effect, and so the beat frequency increases continuously. The theoretical analysis is useful for designing the system for photonic microwave applications.