Double-locked laser diode for microwave photonics applications

Semiconductor lasers subjected to near-resonant external optical injection can exhibit strong oscillations of the output power due to a dynamic instability in the coupling of the gain medium to the circulating optical field. The oscillation frequency depends on the operating point of the injected laser and the strength and frequency offset of the injected optical signal. Adding a reference current modulation to the dc-bias current can induce the oscillation frequency of the optical power to become locked to the reference. Tunable, locked output from 9.5 to 17.1 GHz is demonstrated, with a linewidth below the 1-kHz resolution limit of the measurement apparatus.