Semiconductor waveguide optical gain device with lateral current confinement or optical mode shaping

A method for making an optical device, the method comprising:

• (A) forming a central longitudinal strip of higher-index semiconductor material on a first surface of a substrate, the central longitudinal strip defining longitudinal and lateral directions parallel to the first substrate surface, wherein the substrate includes a semiconductor active layer at the first substrate surface and a bottom doped semiconductor layer beneath and in contact with the active layer;
• (B) forming a pair of longitudinal, laterally spaced-apart strips of higher-index semiconductor material on the first surface of the substrate or on the central longitudinal strip;
• (C) forming one or more current-restricting layers on the first surface of the substrate so that a portion of the central longitudinal strip remains exposed within a longitudinal gap between or through the one or more current-restricting layers, width of the gap being less than width of the central longitudinal strip;
• and
• (D) forming a top doped semiconductor layer on the one or more current-restricting layers and on the central longitudinal strip within the gap, wherein the top and bottom doped layers are of opposite n- or p-doping types, and wherein the higher-index semiconductor materials of the central longitudinal strip and the pair of spaced-apart strips have refractive indices higher than refractive indices of the top and bottom doped layers,
• wherein:
• (E) the semiconductor active layer is arranged so as to emit light and exhibit optical gain at a nominal optical wavelength λ0 through radiative recombination of charge carriers at the active layer resulting from forward-biased drive current flowing between the top and bottom doped layers through the active layer;
• (F) the central longitudinal strip, the active layer, the pair of strips, and the bottom doped layer form an optical waveguide structure, including an optical gain section thereof, arranged as a planar-buried-rib waveguide (PBRWG) that supports one or more optical modes that spatially overlap portions of the bottom doped, top doped, and active layers in the optical gain section, arrangement of the pair of strips resulting in a corresponding optical intensity lateral profile across the active layer of a selected one of the one or more of the optical modes that has a higher fraction of optical intensity within its full width at half maximum intensity (FWHM) compared to a corresponding mode of an otherwise identical reference PBRWG structure that lacks the pair of strips of higher-index semiconductor material;
• (G) the one or more current-restricting layers form one or more drive current structures that include one or more current restrictors that extend medially at least partly across the central longitudinal strip to define a drive current path along which the drive current flows through the active layer in the optical gain section and constrain the drive current to flow through the gap;
• and
• (H) the optical waveguide structure, the one or more drive current structures, or both, are positioned and arranged to result in a selected degree of spatial overlap between (i) a drive current lateral profile across the active layer in the optical gain section and (ii) the corresponding optical intensity lateral profile across the active layer in the optical gain section of the selected one of the one or more optical modes.