Laterally-coupled distributed feedback laser fabricated with electron beam lithography and chemically assisted ion beam etching

The fabrication and optical performance of Laterally-Coupled Distributed Feed-Back (LC-DFB) lasers were investigated. This device differs from a conventional DFB laser in that the grating does not extend inside the laser ridge, rather, gratings adjacent to a single ridge are used to couple to the fringing fields of the active region. This structure allows the entire laser epi-layer structure to be grown in a single step thus eliminating any regrowth steps. A recent design with 1.5 mm cavity length and CAIBE-defined ridges and gratings resulted in pulsed single-mode operation up to 36 mW at 937 nm with as-cleaved facets. The light-current characteristic of this device demonstrated a threshold current of 15 mA and a sidemode suppression ratio of greater than 30 dB. The spectral temperature sensitivity was 0.65 angstrom / °C for this LC-DFB. Also a CW threshold current of 25 mA and an external quantum efficiency of 0.48 mW/mA per facet were measured for a 1 mm cavity length device with anti-reflection coated facets. Fabrication processes and optical characterization are discussed.