CHIRP REDUCTION OF DIRECTLY MODULATED SEMICONDUCTOR-LASERS AT 10 GB SBY STRONG CW LIGHT INJECTION/

The influence of strong light injection on the reduction of the dynami cal linewidth broadening of directly current-modulated semiconductor l asers at high bit rates is theoretically investigated and experimental ly verified for 10 Gb/s NRZ pseudorandom modulation with a large curre nt swing of 40 mA pp. Significant chirp reduction and single-mode oper ation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s an d a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1. 55 mum low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-hau l transmission. The properties of injection-locked bulk DFB and quantu m well DFB lasers with respect to high bit rate modulation have been s ystematically studied by the use of the rate equation formalism. A dyn amically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5 .