Enhanced modulation bandwidth in injection-locked semiconductor lasers

Optical probing of an injection-locked semiconductor laser is used to show significant improvement in the intrinsic broad-band modulation characteristics relative to the free-running case. The regenerative amplification spectra of a weak optical probe in the injection-locked laser are in good agreement with the predictions of a conventional coupled-equation model. Based on the regenerative amplification spectra, the intrinsic modulation characteristic due to a weak injection current modulation can be calculated. It shows approximately a factor of three enhancement of the modulation bandwidth, beyond the K-factor limit of the free-running laser.