Abstract: The semiconductor laser device includes: an activation layer having at least one first quantum dot layer and at least one second quantum dot layer having a longer emission wavelength than the first quantum dot layer. The gain spectrum of the active layer has the maximum values at the first wavelength and the second wavelength longer than the first wavelength corresponding to the emission wavelength of the first quantum dot layer and the emission wavelength of the second quantum dot layer, respectively. The maximum value of the gain spectrum at the first wavelength is defined as the first maximum value, and the maximum value of the gain spectrum at the second wavelength is defined as the second maximum value. The first maximum value is larger than the second maximum value.

Abstract: The semiconductor laser device includes: an activation layer having at least one first quantum dot layer and at least one second quantum dot layer having a longer emission wavelength than the first quantum dot layer. The gain spectrum of the active layer has the maximum values at the first wavelength and the second wavelength longer than the first wavelength corresponding to the emission wavelength of the first quantum dot layer and the emission wavelength of the second quantum dot layer, respectively. The maximum value of the gain spectrum at the first wavelength is defined as the first maximum value, and the maximum value of the gain spectrum at the second wavelength is defined as the second maximum value. The first maximum value is larger than the second maximum value.

Abstract: A vertical cavity surface emitting laser includes a first laminate including first semiconductor layers having a first Al composition, and second semiconductor layers having a second Al composition greater than the first Al composition; a current confinement structure including a current aperture and a current blocker; a first compound semiconductor layer adjacent to the current confinement structure; and a second compound semiconductor layer adjacent to the first laminate and the first compound semiconductor layer. The first compound semiconductor layer has a first aluminum profile changing monotonously in a direction from the first laminate to the current confinement structure from a first minimum Al composition within a range greater than the first Al composition and smaller than the second Al composition to a first maximum Al composition. The second compound semiconductor layer has an Al composition greater than the first Al composition and smaller than the first maximum Al composition.

Abstract: A vertical cavity surface emitting laser includes: a supporting base; and a post including an upper distributed Bragg reflecting region, an active layer, and a lower distributed Bragg reflecting region. The upper distributed Bragg reflecting region, the active layer, and the lower distributed Bragg reflecting region are arranged on the supporting base. The lower distributed Bragg reflecting region includes first semiconductor layers and second semiconductor layers alternately with each of the first semiconductor layers having a refractive index lower than that of each of the second semiconductor layers. The upper distributed Bragg reflecting region includes first layers and second layers alternately with each of the first layers having a group III-V compound semiconductor portion and a group III oxide portion. The group III-V compound semiconductor portion contains aluminum as a group III constituent element, and the group III oxide portion surrounds the group III-V compound semiconductor portion.

Abstract: A vertical cavity surface-emitting laser including: a substrate having a main surface; and a post structure mounted on the main surface. The post structure includes an active layer and a carrier confinement structure. The carrier confinement structure includes a first region and a second region having a higher resistivity than the first region. The first region has an edge, and a first to a third reference line segments. A first length of the first reference line segment is longest among lengths of line segments joining any two points on the edge and extending in a direction of the III-V group semiconductor. The first length is greater than a sum of a second length of the second reference line segment and a third length of the third reference line segment. The third length is smaller than the second length and is zero or more.

Abstract: A vertical cavity surface emitting laser includes a first laminate including first semiconductor layers having a first Al composition, and second semiconductor layers having a second Al composition greater than the first Al composition; a current confinement structure including a current aperture and a current blocker; a first compound semiconductor layer adjacent to the current confinement structure; and a second compound semiconductor layer adjacent to the first laminate and the first compound semiconductor layer. The first compound semiconductor layer has a first aluminum profile changing monotonously in a direction from the first laminate to the current confinement structure from a first minimum Al composition within a range greater than the first Al composition and smaller than the second Al composition to a first maximum Al composition. The second compound semiconductor layer has an Al composition greater than the first Al composition and smaller than the first maximum Al composition.

Abstract: A vertical cavity surface-emitting laser including: a substrate having a main surface; and a post structure mounted on the main surface. The post structure includes an active layer and a carrier confinement structure. The carrier confinement structure includes a first region and a second region having a higher resistivity than the first region. The first region has an edge, and a first to a third reference line segments. A first length of the first reference line segment is longest among lengths of line segments joining any two points on the edge and extending in a [1-10] direction of the III-V group semiconductor. The first length is greater than a sum of a second length of the second reference line segment and a third length of the third reference line segment. The third length is smaller than the second length and is zero or more.

Abstract: A vertical cavity surface emitting laser includes: a supporting base: and a post including an upper distributed Bragg reflecting region, an active layer, and a lower distributed Bragg reflecting region. The upper distributed Bragg reflecting region, the active layer, and the lower distributed Bragg reflecting region are arranged on the supporting base. The lower distributed Bragg reflecting region includes first semiconductor layers and second semiconductor layers alternately arranged. The first semiconductor layers each have a refractive index lower than that of each of the second semiconductor layers. The upper distributed Bragg reflecting region includes first layers and second layers alternately arranged. The first layers each have a group III-V compound semiconductor portion and a group III oxide portion. The group III-V compound semiconductor portion contains aluminum as a group III constituent element, and the group III oxide portion surrounds the group III-V compound semiconductor portion.

Abstract: A surface-emitting semiconductor laser includes a stacked semiconductor layer on a substrate; and a post including a current constriction structure including an oxide portion and a semiconductor portion, and an active layer. The post includes a peripheral portion and first to fourth portions. The oxide portion is located in the second and fourth portions, and the semiconductor portion is located in the first and third portions. The post includes first to fourth level parts that are sequentially arranged in a direction from the substrate to the stacked semiconductor layer. The active layer and the current constriction structure are located in the first and second level parts, respectively. The peripheral portion includes a first region having a first hydrogen concentration. The second level part includes a second region having a second hydrogen concentration. The first and second hydrogen concentrations are larger than that of the first portion.

Abstract: A cable for transmitting electromagnetic waves is disclosed. The cable is a cable for transmitting electromagnetic waves, and includes a core extending along a longitudinal direction of the cable, the core including a dielectric, a sleeve extending along the longitudinal direction of the cable while surrounding the core so as to provide a cavity between the core and the sleeve, the sleeve including a dielectric, and a support that supports the core in the cavity in the sleeve, the support including a dielectric.

Abstract: Provided are an optical element and a wavelength monitor capable of detecting a wavelength with high accuracy and at high speed while suppressing a size. The optical element includes: a branch waveguide section configured to branch an input light beam and generate two outputs routed via paths having mutually different optical path lengths; and an optical synthesis section configured to synthesize the two outputs and output two optical signals having different light intensities with regards to a wavelength of the input light beam and exhibiting a mutual phase difference.

Abstract: A coherent mixer includes a multi-mode waveguide that has a side surface and an end; a waveguide group including a plurality of semiconductor regions connected to the end; a first semiconductor region that has a side surface extending substantially parallel to the side surface of the multi-mode waveguide; and an external semiconductor region having a side surface extending substantially parallel to an edge of the waveguide group. The side surface of the semiconductor region is spaced apart from the side surface of the multi-mode waveguide by a distance smaller than or equal to a reference value. The side surface of the external semiconductor region is spaced apart from the edge of the waveguide group by a distance smaller than or equal to the reference value. The reference value is a maximum value of distances between arbitrary adjacent semiconductor regions in the waveguide group.

Abstract: A spot-size converter includes a cladding layer having a principal surface; a first core layer disposed on the principal surface and having a light input/output portion and a first transition portion having a width W1, the light input/output portion being coupled to the first transition portion and having a width that monotonously decreases in a first direction from the light input/output portion toward the first transition portion; and a second core layer disposed on the principal surface, the second core layer having a second transition portion and a propagation portion coupled to the second transition portion, the second transition portion having a width W2 . The first core layer has a refractive index between refractive indices of the second core layer and the cladding layer. The first transition portion and the second transition portion are disposed with a gap therebetween and optically coupled to each other. A ratio (W1/W2) of the width W1 to the width W2 monotonously decreases in the first direction.

Abstract: A coherent mixer includes a substrate including a principal surface, the principal surface having a first area and a second area; a multi-mode interference device provided on the first area of the substrate; a light-receiving device provided on the second area of the substrate, the light-receiving device including a plurality of waveguide-type photodiodes; a first input waveguide optically coupled to the multi-mode interference device; a second input waveguide optically coupled to the multi-mode interference device; a plurality of optical waveguides optically coupling the multi-mode interference device to the plurality of waveguide-type photodiodes; and a protective layer covering the first and second areas of the substrate, the protective layer covering the plurality of waveguide-type photodiodes. The protective layer has an opening in the first area of the substrate. In addition, the multi-mode interference device has a surface that is at least partially exposed at the opening of the protective layer.

Abstract: A semiconductor optical device includes a light receiving device; an optical waveguide having a mesa structure, the optical waveguide including first, second, third, and fourth waveguide portions; and a passivation layer provided on a side surface of the light receiving device. The mesa structure in the second waveguide portion has a width increasing along the waveguide axis, and the mesa structure in the third waveguide portion has a width decreasing along the waveguide axis. The second waveguide portion includes first and second regions, the first region being optically coupled to the first waveguide portion and the second region being optically coupled to the third waveguide portion. The passivation layer is provided on side surfaces of the mesa structure in the second region, the third waveguide portion, and the fourth waveguide portion. The mesa structures in the first waveguide portion and the first region have side surfaces without the passivation layer.

Abstract: A polarization control device includes a MMI device having primary-side and secondary-side end-faces; a first phase shifter optically coupled to a first port in the primary-side end-face; a first optical waveguide optically coupled via the first phase shifter to the first port in the primary-side end-face; a second optical waveguide optically coupled to a second port in the primary-side end-face; and a tapered waveguide optically coupled to a first port in the secondary-side end-face. The first and second ports in the primary-side end-face are located on first and second axes, respectively. The first port in the secondary-side end-face is located on a third axis located between the first and second axes. The first, second, and third axes extend in a direction from the primary-side end-face to the secondary-side end-face. The tapered waveguide has a width decreasing in a direction from one end to the other end of the tapered waveguide.

Abstract: Provided are an optical element and a wavelength monitor capable of detecting a wavelength with high accuracy and at high speed while suppressing a size. The optical element includes: a branch waveguide section configured to branch an input light beam and generate two outputs routed via paths having mutually different optical path lengths; and an optical synthesis section configured to synthesize the two outputs and output two optical signals having different light intensities with regards to a wavelength of the input light beam and exhibiting a mutual phase difference.

Abstract: A coherent mixer includes a multi-mode waveguide that has a side surface and an end; a waveguide group including a plurality of semiconductor regions connected to the end; a first semiconductor region that has a side surface extending substantially parallel to the side surface of the multi-mode waveguide; and an external semiconductor region having a side surface extending substantially parallel to an edge of the waveguide group. The side surface of the semiconductor region is spaced apart from the side surface of the multi-mode waveguide by a distance smaller than or equal to a reference value. The side surface of the external semiconductor region is spaced apart from the edge of the waveguide group by a distance smaller than or equal to the reference value. The reference value is a maximum value of distances between arbitrary adjacent semiconductor regions in the waveguide group.

Abstract: A polarization control device includes a MMI device having primary-side and secondary-side end-faces; a first phase shifter optically coupled to a first port in the primary-side end-face; a first optical waveguide optically coupled via the first phase shifter to the first port in the primary-side end-face; a second optical waveguide optically coupled to a second port in the primary-side end-face; and a tapered waveguide optically coupled to a first port in the secondary-side end-face. The first and second ports in the primary-side end-face are located on first and second axes, respectively. The first port in the secondary-side end-face is located on a third axis located between the first and second axes. The first, second, and third axes extend in a direction from the primary-side end-face to the secondary-side end-face. The tapered waveguide has a width decreasing in a direction from one end to the other end of the tapered waveguide.

Abstract: A DP QPSK optical modulator includes an input port; an optical branching unit; an optical modulation unit having first through fourth Mach-Zehnder interferometers; a first phase-change unit connected to the third Mach-Zehnder interferometer; a second phase-change unit connected to the fourth Mach-Zehnder interferometer; an optical multiplexer; and a multimode interference coupler including a multimode interference waveguide, first through third input ports, and an output port having a taper-shaped waveguide. The first Mach-Zehnder interferometer is connected to the first input port. One end of the optical multiplexer is connected to the second Mach-Zehnder interferometer and the third Mach-Zehnder interferometer via the first phase change unit. The other end of the optical multiplexer is connected to the second input port. The fourth Mach-Zehnder interferometer is connected to the third input port via the second phase-change unit.