A surface-emitting semiconductor light-emitting device includes a first semiconductor layers, an active layer on the first semiconductor layer, a photonic crystal layer on the active layer and a second semiconductor layer on the photonic crystal layer. The photonic crystal layer include first protrusions in a first region and second protrusions in a second region. A spacing of adjacent first protrusions is greater than a spacing of adjacent second protrusions. The second semiconductor layer includes a first layer and a second layer on the first layer. The first layer covers first and second protrusions so that a first space remains between the adjacent first protrusions. The first layer includes a first portion provided between the adjacent second protrusions. The second layer includes a second portion provided between the adjacent first protrusions. The first space between the adjacent first protrusions is filled with the second portion of the second layer.

Semiconductor laser architectures that provide weak index guiding of interband cascade lasers (ICLs) processed on a native III-V substrate and of ICLs grown on silicon or integrated on silicon by heterogeneous bonding. Weak index guiding of a ridge waveguide semiconductor laser can enhance the stability of lasing in the fundamental lateral mode, so as to allow a wider ridge to maintain stable single-lateral-mode operation.

A semiconductor laser wafer includes a substrate, a first semiconductor layer, an active layer, a second semiconductor layer, and a composition evaluation layer. The active layer is provided on the first semiconductor layer; multiple periods of pairs of a light-emitting multi-quantum well region and an injection multi-quantum well region are stacked in the active layer; the light-emitting multi-quantum well region is made of a first compound semiconductor and a second compound semiconductor. The second semiconductor layer is provided on the active layer. The composition evaluation layer is provided above the active layer and includes a first film and a second film; the first film is made of the first compound semiconductor and has a first thickness; and the second film is made of the second compound semiconductor and has a second thickness.

A semiconductor laser wafer includes a substrate, a first semiconductor layer, an active layer, a second semiconductor layer, and a composition evaluation layer. The active layer is provided on the first semiconductor layer; multiple periods of pairs of a light-emitting multi-quantum well region and an injection multi-quantum well region are stacked in the active layer; the light-emitting multi-quantum well region is made of a first compound semiconductor and a second compound semiconductor. The second semiconductor layer is provided on the active layer. The composition evaluation layer is provided above the active layer and includes a first film and a second film; the first film is made of the first compound semiconductor and has a first thickness; and the second film is made of the second compound semiconductor and has a second thickness.

A surface-emitting semiconductor light-emitting device includes a first semiconductor layers, an active layer on the first semiconductor layer, a photonic crystal layer on the active layer and a second semiconductor layer on the photonic crystal layer. The photonic crystal layer include first protrusions in a first region and second protrusions in a second region. A spacing of adjacent first protrusions is greater than a spacing of adjacent second protrusions. The second semiconductor layer includes a first layer and a second layer on the first layer. The first layer covers first and second protrusions so that a first space remains between the adjacent first protrusions. The first layer includes a first portion provided between the adjacent second protrusions. The second layer includes a second portion provided between the adjacent first protrusions. The first space between the adjacent first protrusions is filled with the second portion of the second layer.

A quantum cascade laser device has a light-absorbing cover member located between one emission end face of a quantum cascade laser element and an emission window of a housing. The emission end face and an opposing surface of a submount with respect to the cover member are flush with each other. The cover member has an opening at a position opposing the emission end face. The opening has a tapered first opening part increasing its diameter from the emission end face side to the emission window side and a second opening part formed with a fixed diameter not smaller than the smallest diameter of the first opening part.

A quantum cascade laser device has a light-absorbing cover member located between one emission end face of a quantum cascade laser element and an emission window of a housing. The emission end face and an opposing surface of a submount with respect to the cover member are flush with each other. The cover member has an opening at a position opposing the emission end face. The opening has a tapered first opening part increasing its diameter from the emission end face side to the emission window side and a second opening part formed with a fixed diameter not smaller than the smallest diameter of the first opening part.

A thermal emission source capable of switching the intensity of light at a high response speed similarly to a photoelectric conversion element. A thermal emission source includes: a two-dimensional photonic crystal including a slab in which an n-layer made of an n-type semiconductor, a quantum well structure layer having a quantum well structure, and a p-layer made of a p-type semiconductor are stacked in the mentioned order in the thickness direction, wherein modified refractive index areas (air holes) whose refractive index differs from the refractive indices of the n-layer, the p-layer and the quantum well structure layer are cyclically arranged in the slab so as to resonate with a specific wavelength of light corresponding to a transition energy between the subbands in a quantum well in the quantum well structure layer; and a p-type electrode and an n-type electrode for applying, to the slab, a voltage which is negative on the side of the p-layer and positive on the side of the n-layer.

A thermal emission source capable of switching the intensity of light at a high response speed similarly to a photoelectric conversion element. A thermal emission source includes: a two-dimensional photonic crystal including a slab in which an n-layer made of an n-type semiconductor, a quantum well structure layer having a quantum well structure, and a p-layer made of a p-type semiconductor are stacked in the mentioned order in the thickness direction, wherein modified refractive index areas (air holes) whose refractive index differs from the refractive indices of the n-layer, the p-layer and the quantum well structure layer are cyclically arranged in the slab so as to resonate with a specific wavelength of light corresponding to a transition energy between the subbands in a quantum well in the quantum well structure layer; and a p-type electrode and an n-type electrode for applying, to the slab, a voltage which is negative on the side of the p-layer and positive on the side of the n-layer.

Semiconductor laser architectures that provide weak index guiding of interband cascade lasers (ICLs) processed on a native III-V substrate and of ICLs grown on silicon or integrated on silicon by heterogeneous bonding. Weak index guiding of a ridge waveguide semiconductor laser can enhance the stability of lasing in the fundamental lateral mode, so as to allow a wider ridge to maintain stable single-lateral-mode operation.