Semiconductor waveguide optical gain device with lateral current confinement

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 surface of the substrate, wherein the substrate includes a semiconductor active layer at the first surface of the substrate and a bottom doped semiconductor layer beneath and in contact with the active layer;
• (B) 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
• (C) 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 material of the central longitudinal strip has a refractive index higher than refractive indices of the top and bottom doped layers,
• wherein:
• (D) 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;
• (E) the central longitudinal strip, the active layer, 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, the one or more optical modes being (i) confined laterally by the central longitudinal strip and (ii) confined by the active layer only vertically;
• (F) 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
• (G) the width of the gap results in reduced width of a drive current lateral profile across the active layer in the optical gain section, compared to such drive current lateral profile width in an otherwise identical reference PBRWG structure wherein the width of the gap is equal to the width of the central longitudinal strip thereof, which in turn results in a selected degree of increased spatial overlap between the drive current lateral profile and a corresponding optical intensity lateral profile across the active layer in the optical gain section of a selected one of the one or more optical modes, compared to such spatial overlap in the otherwise identical reference PBRWG structure.