Bandwidth enhancement and chirp reduction in DBR lasers by strong optical injection

Abstract

Summary form only given.We have observed modulation bandwidth enhancement to 28 GHz and evidence of reduced chirp, beyond the optimally tuned free running case, in strongly injection-locked DBR lasers. Bandwidth enhancement occurs because the total modal photon density depends on the phase between the master and slave fields, which varies during modulation due to the dependence of index on carrier density. This results in an increased coupling between the carriers and photons, giving an effectively higher differential gain. This effect appears to be stronger than the similar amplitude-phase coupling that occurs with detuned loading. Chirp reduction occurs only for very strong injection, which can be explained by the fact that chirp reduction can only be achieved for modulation frequencies less than the locking range, which increases with injected power. For higher frequencies, the chirp reduction due to detuned loading dominates.