Experimental observation of chirp reduction in bandwidth-enhanced semiconductor lasers subject to strong optical injection

An optically injection-locked semiconductor laser under direct current modulation is experimentally studied. Significant increase in the relaxation resonance frequency is first demonstrated, implying the same degree of enhancement in modulation bandwidth. Under bandwidth-enhanced operating conditions, substantial reduction in frequency chirping is observed, which demonstrates that significant bandwidth enhancement and chirp reduction are simultaneously achieved in experiment. Chirp reduction as a function of modulation frequency is also investigated. Substantial chirp reduction happens at low modulation frequency. However, the frequency chirping reduces less with increasing modulation frequency. The frequency chirping of the injection-locked laser approaches to that of the free-running laser at high modulation frequency. Effective chirping parameter is introduced and analyzed for the injection-locked laser to study the physical mechanism behind the chirp reduction. (C) 2003 Elsevier Science B.V. All rights reserved.