Self-Aligned Ridge-Waveguide DFB Lasers Emitting at 1.55 µm: Ridge-Width Dependence

Self-aligned ridge-waveguide (SA-RG) DFB lasers emitting at 1.55 µm have been fabricated utilizing the MOVPE growth technique and a self-aligning process. The ridge-width dependence of the threshold current and the optical lateral mode is investigated. Ridge-waveguide lasers with a thin active layer of 0.1 µm for low threshold current provide sufficient index guiding. The fabricated SA-RG DFB laser has a threshold current of as low as 29 mA. The threshold current density increases as the ridge width becomes narrower than 10 µm. This is explained by the electron diffusion in the active layer and the diffusion length is experimentally estimated to be 2–5 µm. The measured far-field pattern parallel to the junction shows a single-lobe pattern at a ridge width of less than 10 µm.