Narrow-linewidth distributed feedback lasers with laterally coupled ridge-waveguide surface gratings fabricated using nanoimprint lithography

Abstract

The conventional distributed feedback (DFB) edge-emitting lasers with buried gratings require two or more epitaxial growth steps. To avoid the problematic overgrowth we have used laterally-corrugated ridge-waveguide surface gratings, which also enable easy integration of the resulting laterally-coupled DFB (LC-DFB) lasers with other devices and are applicable to different materials, including Al-containing ones. The paper presents the modeling and design particularities of LC-DFB lasers, the fabrication process, involving a highly productive and cost-effective UVnanoimprint lithography technique, and the characteristics obtained for the LC-DFB lasers fabricated from GaAs-, GaSband InP-based epiwafers. The first batches of GaAs-based LC-DFB lasers, emitting at 894 nm, GaSb-based LC-DFB lasers emitting at 1.946 μm and InP-based LC-DFB lasers, emitting at 1.55 μm had relatively low threshold currents, a high side-mode-suppression-ratio and exhibited linewidths in the range of 1 MHz and below, showing that the LC-DFB lasers are an effective low-cost alternative for the conventional buried-grating DFB lasers.