Dynamic responses of widely tunable sampled grating DBR lasers

The modulation bandwidth, dynamic mode suppression ratio, and wavelength chirp of directly modulated sampled grating DBR lasers have been measured. Although the tuning range can be up to an order of magnitude larger than in simple DBR lasers, the chirp is about the same or better over a wide range of operation parameters. The modulation bandwidth was in excess of 4 GHz and the dynamic MSR remained larger than 40 dB as long as the current did not swing below threshold. The linewidth enhancement factor was extracted from the measured chirp parameters and ranged from three to eight for different lasing wavelengths of the tunable lasers. The dispersion of the linewidth enhancement factor is consistent with published theoretical predictions.