Bandwidth enhancement and broadband noise reduction in injection-locked semiconductor lasers

Abstract

Optical injection modifies the resonant coupling between the oscillating field and free carriers in a semiconductor laser. Resonant oscillations and chaotic dynamics have been observed. However, the region of unstable locking is bounded as the injection level is increased. The linear analysis predicts improved bandwidth and stable modulation characteristics at injection levels above those previously analyzed. An injection-locked semiconductor laser can have a modulation bandwidth greater than the limit for the free-running laser set by the K-factor. Significantly, this is achieved using constant amplitude injection from a stable, i.e. low noise, master laser which can have very poor high-frequency performance characteristics. We have investigated the bandwidth enhancement in a conventional, edge-emitting, quantum-well laser diode. The optical spectrum of the free-running laser diode is given. Previously, we have shown that injection at the free running frequency induces strong modifications in both the frequency and damping of the carrier-field resonance with increasing injection. Here, we show that for very high injection levels where the injected power is on the order of 1-10% of the circulating power, the resonance frequency continues to increase but that the resonance again becomes damped and stable operation is achieved.