A semiconductor laser comprises a window structure part including a low resistance active layer formed in end face regions, to have a lower resistance than an active layer located inward with respect to the end face regions. A length between the front end of the contact layer and the front end face is longer by 10 μm or more than a length of a front-end-face side window structure part, and is shorter than a length between the front end face and the rear end of the contact layer. A length between an end of a rear side electrode on the side of the front end face and the front end face is 1.2 times or more a substrate thickness of a substrate, and is shorter than a length between the front end face and an end of the rear side electrode on the side of the rear end face.

A semiconductor laser comprises a window structure part including a low resistance active layer formed in end face regions, to have a lower resistance than an active layer located inward with respect to the end face regions. A length between the front end of the contact layer and the front end face is longer by 10 μm or more than a length of a front-end-face side window structure part, and is shorter than a length between the front end face and the rear end of the contact layer. A length between an end of a rear side electrode on the side of the front end face and the front end face is 1.2 times or more a substrate thickness of a substrate, and is shorter than a length between the front end face and an end of the rear side electrode on the side of the rear end face.

A semiconductor layer structure may include a substrate, a buffer layer formed on the substrate, and a set of epitaxial layers formed on the buffer layer. The buffer layer may have a thickness that is greater than 2 micrometers (μm). The set of epitaxial layers may include a quantum well layer. A quantum well intermixing region may be formed in association with the quantum well layer and a material diffused from a region of a surface of the semiconductor layer structure.

In a semiconductor laser device, a semiconductor layer includes a first groove formed on both sides of a ridge, a pair of second recesses facing each other and between which the ridge is interposed on a side of a light emitting surface, and a pair of third grooves in parallel to the first groove from the light emitting surface and interposing the ridge therebetween.

A semiconductor laser element that includes a semiconductor layer including a waveguide formed in an intra-layer direction of the semiconductor layer and a window region formed in a front-side end face of the waveguide, has a current-laser optical output characteristic in which, at an operating temperature of 25° C. ±3° C., a laser optical output has a maximum value at a first driving current value and the laser optical output is at most 20% of the maximum value at a second driving current value greater than the first driving current value, and is not damaged at the second driving current value.

A semiconductor laser device includes: a first conductivity side semiconductor layer, an active layer; and a second conductivity side semiconductor layer. The second conductivity side semiconductor layer includes a first semiconductor layer and a second semiconductor layer, the first semiconductor layer being closer to the active layer than the second semiconductor layer is. The second semiconductor layer defines a width of a current injection region for injecting current into an optical waveguide. The current injection region includes a width varying region in which a width varies. S1>S2, where S1 denotes a width of the width varying region on a front end face side, and S2 denotes a width of the width varying region on a rear end face side.

A semiconductor laser device includes: a first conductivity side semiconductor layer, an active layer; and a second conductivity side semiconductor layer. The second conductivity side semiconductor layer includes a first semiconductor layer and a second semiconductor layer, the first semiconductor layer being closer to the active layer than the second semiconductor layer is. The second semiconductor layer defines a width of a current injection region for injecting current into an optical waveguide. The current injection region includes a width varying region in which a width varies. S1>S2, where S1 denotes a width of the width varying region on a front end face side, and S2 denotes a width of the width varying region on a rear end face side.

A quantum cascade semiconductor laser includes a laser structure having a first area including an end face, a second area, and a third area; a metal layer provided on a major surface in the third area; a separation area provided on the major surface; and a reflector provided on the laser structure. The reflector includes a dielectric film and a metal reflecting film provided on the end face and the separation area. The separation area has a first portion, a second portion, and a third portion. The metal layer has an edge separated from the end face in the third area. The contact layer has an edge separated from the end face in the third area. The first portion projects more than the second portion over the semiconductor mesa. The third portion projects more than the second portion over the semiconductor mesa.

A semiconductor laser includes a semiconductor layer including end faces and at least one of the end faces is configured as a light emission end face. The semiconductor layer includes a waveguide and a light window structure region. The waveguide has a first width and is extended between the end faces. The light window structure region includes an opening having a second width greater than the first width arranged along the waveguide and is formed continuously or intermittently from one to another of the end faces.

A semiconductor laser includes a semiconductor layer including end faces and at least one of the end faces is configured as a light emission end face. The semiconductor layer includes a waveguide and a light window structure region. The waveguide has a first width and is extended between the end faces. The light window structure region includes an opening having a second width greater than the first width arranged along the waveguide and is formed continuously or intermittently from one to another of the end faces.