Development of high-speed directly-modulated DFB and DBR lasers with surface gratings.

The conventional distributed feedback and distributed Bragg reflector edge-emitting lasers employ buried gratings, which require two or more epitaxial growth steps. By using lateral corrugations of the ridge-waveguide as surface gratings the epitaxial overgrowth is avoided, reducing the fabrication complexity, increasing the yield and reducing the fabrication cost. The surface gratings are applicable to different materials, including Al-containing ones and can be easily integrated in complex device structures and photonic circuits. Single-contact and multiple contact edge-emitting lasers with laterally-corrugated ridge waveguide gratings have been developed both on GaAs and InP substrates with the aim to exploit the photon-photon resonance in order to extend their direct modulation bandwidth. The paper reports on the characteristics of such surface-grating-based lasers emitting both at 1.3 and 1.55 μm and presents the photon-photon resonance extended small-signal modulation bandwidth (> 20 GHz) achieved with a 1.6 mm long single-contact device under direct modulation. Similarly structured devices, with shorter cavity lengths are expected to exceed 40 GHz smallsignal modulation bandwidth under direct modulation.