There is provided a configuration which includes: a burying layer which has a current narrowing window where portions protruding onto a top part of a ridge stripe are opposed to each other with an interval therebetween narrower than a width of the top part; and a diffraction grating in which a λ/4 phase shifter is placed at an intermediate portion in a light traveling direction; wherein a sectional shape of the current narrowing window varies depending on a position in the light traveling direction so that, at a region where the λ/4 phase shifter is placed, a resistance of a current path from a second cladding layer to a first cladding layer through the current narrowing window is minimum.

The present invention is characterized by comprising: forming a stacked structure in which a lower cladding layer, an active layer and an upper cladding layer are stacked on an InP substrate in a shape having a mesa stripe structure; forming a first insulation film on the stacked structure by a sputtering method; forming a second insulation film thinner than the first insulation film, on the first insulation film by a plasma CVD method at a film forming temperature higher than that when the first insulation film has been formed; and forming a first electrode on the upper cladding layer, and forming a second electrode on a back surface of the InP substrate.

A QCL may include a substrate, an emitting facet, and semiconductor layers adjacent the substrate and defining an active region. The active region may have a longitudinal axis canted at an oblique angle to the emitting facet of the substrate. The QCL may include an optical grating being adjacent the active region and configured to emit one of a CW laser output or a pulsed laser output through the emitting facet of substrate.

A semiconductor optical device includes: a semiconductor layer having a projection; a multiple quantum well layer on the projection; a pair of first semiconductor layers in contact with the mesa stripe structure on respective both sides; a pair of second semiconductor layers on the semiconductor layer; a pair of resin layers above the second semiconductor layers; a pair of third semiconductor layers on the second semiconductor layers, each third semiconductor layer surrounding a corresponding one of the resin layers, the third semiconductor layers being different in constituent material from the second semiconductor layers; a first electrode on the semiconductor layer; and a second electrode including a mesa electrode on the mesa stripe structure, a lead-out electrode extending in the second direction from the mesa electrode, and a pad electrode above one of the resin layers, the pad electrode being connected to the lead-out electrode.

A heterostructure laser is provided comprising an epitaxially grown substrate of first dopant type, an active region and layer of second dopant type, a narrow mesa having less than 20% open area and a side wall slope of less than 85 degrees, wherein said narrow mesa is etched through the active region and layer of second dopant type using in-situ MOCVD, a plurality of current blocking layers, an overclad layer and a contact layer of second dopant type, and an isolation mesa incorporating the narrow mesa, wherein the isolation mesa is etched through the active region, layer of second dopant type and plurality of current blocking layers and wherein the plurality of current blocking layers is grown without exposure to oxygen.

There is provided a method for fabricating a corrugated buried heterostructure laser, including patterning a dielectric layer coating a substrate having a <0-11> direction to obtain a hollow corrugated structure. The hollow corrugated structure includes a central portion and regularly spaced-apart tabs laterally extending from the central portion and aligned with the <0-11> direction. The method also includes, in a single metal organic chemical vapour deposition run, forming an active region in the hollow corrugated structure to obtain the corrugated buried heterostructure laser. The single run combines selective area growth, p-dopant diffusion and etching techniques. There is also provided a corrugated buried heterostructure laser including a substrate having a <0-11> direction, a corrugated structure defined in the substrate and including a central portion and regularly spaced-apart tabs laterally extending from the central portion and aligned with the <0-11> direction, and an active region grown in the corrugated structure.

An insulating film (10) having an opening (11) is formed on a contact layer (7). A shape stabilization layer (8) having an inclined surface (9) is formed on the contact layer (7) in a peripheral portion of the opening (11). An underlying metal (12) covers an upper surface of the contact layer (7) exposed through the opening (11) and the inclined surface (9). A plating (13) is formed on the underlying metal (12).

The semiconductor laser device comprises a laser part, a waveguide for propagating laser light emitted by the laser part, and a photodetector for detecting the laser light which are formed on the same semiconductor substrate. The photodetector includes a p-type contact layer which is formed above the side of the waveguide on the side opposite to the semiconductor substrate and is connected to an anode electrode, an n-type contact layer connected to a cathode electrode, and an undoped layer formed between the p-type contact layer and the n-type contact layer. The undoped layer and the n-type contact layer in the photodetector include a main light receiving part disposed above the waveguide so as to encompass the waveguide, and an enlarged part disposed so as not to encompass the waveguide while connected to the main light receiving part.

A semiconductor optical device includes a substrate containing silicon, and a semiconductor element bonded to the substrate, the semiconductor element being formed of a compound semiconductor and having an optical gain. The substrate includes a waveguide and a first region connected to the waveguide in an extension direction of the waveguide. The first region includes a plurality of recesses and a plurality of protrusions. Each of the plurality of recesses is recessed in a thickness direction of the substrate compared to a surface of the substrate to which the semiconductor element is bonded. Each of the plurality of protrusions protrudes in the thickness direction of the substrate from bottom surfaces of the plurality of recesses. The plurality of recesses and the plurality of protrusions are alternately disposed in a direction intersecting with the extension direction of the waveguide. The semiconductor element is bonded to the first region.

A germanium waveguide is formed from a P-type silicon substrate that is coated with a heavily-doped N-type germanium layer and a first N-type doped silicon layer. Trenches are etched into the silicon substrate to form a stack of a substrate strip, a germanium strip, and a first silicon strip. This structure is then coated with a silicon nitride layer.