Examples of the present disclosure include a tunable laser comprising a waveguide including gain section. The waveguide overlies and is optically coupled to another waveguide. The another waveguide has a reflector at one end. A laser cavity is formed in the waveguides.

A waveguide heterostructure for a semiconductor laser with an active part, comprising an active region layer depending of the type of semiconductor used, which is sandwiched between an electrode layer and a substrate, usable for dispersion compensation in a semiconductor laser frequency comb setup, an optical frequency comb setup and a manufacturing method.

A semiconductor structure can comprise a plurality of first semiconductor layers comprising wide bandgap semiconductor layers, a narrow bandgap semiconductor layer, and a chirp layer between the plurality of first semiconductor layers and the narrow bandgap semiconductor layer. The values of overlap integrals between different electron wavefunctions in a conduction band of the chirp layer can be less than 0.05 for intersubband transition energies greater than 1.0 eV, and/or the values of overlaps between electron wavefunctions and barrier centers in a conduction band of the chirp layer can be less than 0.3 nm.sup.−1, when the structure is biased at an operating potential. The chirp layer can comprise a short-period superlattice with alternating wide bandgap barrier layers and narrow bandgap well layers, wherein the thickness of the barrier layers, or the well layers, or the thickness of both the barrier and well layers changes throughout the chirp layer.

An optical semiconductor device outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The optical semiconductor device includes a separate confinement heterostructure layer positioned between the quantum well active layer and the n-type cladding layer. The optical semiconductor device further includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and the n-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The quantum well active layer is doped with 0.3 to 1×10.sup.18/cm.sup.3 of n-type impurity.

The invention relates to an apparatus, system and method for reducing or eliminating polarization effects in a compound semiconductor quantum well optical gain structure including the quantum confined Stark effect (QCSE) and carrier leakage effects. The system comprises a quantum well formed by a monotonic, stepwise and/or continuous compositional grading of a first quantum well interface toward a reduced bandgap, also including a monotonic, stepwise or continuous compositional grading of a second quantum well interface toward an increased bandgap thereby creating a quantum well shape that is substantially symmetric under the influence of electrostatic and/or electrodynamic fields. The system also comprises an electron blocking layer formed by a stepwise or continuous compositional grading starting from the maximum bandgap of the quantum well and increasing toward a larger bandgap, thereby creating a barrier shape with reduced electron sheet charge due to the influence of electrostatic fields.

An embodiment relates to a surface-emitting laser device and a light-emitting device including same. A surface-emitting laser device according to the embodiment can include: a first reflective layer; an active area disposed on the first reflective layer; an aperture area disposed on the active area; and a second reflective layer disposed on the aperture area. The second reflective layer can include: a first AlGaAs-based layer comprising Al.sub.x1Ga.sub.(1-x1)As (wherein 0<X1<0.2); a second AlGaAs-based layer disposed on the first AlGaAs-based layer and comprising Al.sub.x2Ga.sub.(1-x2)As (wherein 0.8<X2<1.0); and an AlGaAs-based transition area disposed between the first AlGaAs-based layer and the second AlGaAs-based layer. The AlGaAs-based transition area can include: a third AlGaAs-based layer comprising Al.sub.x3Ga.sub.(1-x3)As (wherein 0<X3<0.2); and a fourth AlGaAs-based layer comprising Al.sub.x4Ga.sub.(1-x4)As (wherein 0.8<X4<1.0).

A light emitting device according to an embodiment of the present disclosure includes: a first layer including Al.sub.x2In.sub.x1Ga.sub.(1-x1-x2) N (0<x1<1, 0≤x2<1); a second layer that is provided on the first layer and includes Al.sub.y2In.sub.y1Ga.sub.(1-y1-y2) N (0<y1<1, 0≤y2<1) that is lattice relaxed with respect to the first layer; and a third layer that is provided on the second layer, includes Al.sub.z2In.sub.z1Ga.sub.(1-z1-z2) N (0<z1<1, 0≤z2<1) that is lattice relaxed with respect to the second layer, and includes an active layer. A lattice constant aGAN of GaN in an in-plane direction, a lattice constant al of the first layer in an in-plane direction, a lattice constant a2 of the second layer in an in-plane direction, and a lattice constant a3 of the third layer in an in-plane direction have a relationship of aGAN<a2<a1, a3.

A semiconductor laser element includes: an n-type cladding layer disposed above an n-type semiconductor substrate (a chip-like substrate); an active layer disposed above the n-type cladding layer; and a p-type cladding layer disposed above the active layer, in which the active layer includes a well layer and a barrier layer, an energy band gap of the barrier layer is larger than an energy band gap of the n-type cladding layer, and a refractive index of the barrier layer is higher than a refractive index of the n-type cladding layer.

A semiconductor structure can comprise a plurality of first semiconductor layers comprising wide bandgap semiconductor layers, a narrow bandgap semiconductor layer, and a chirp layer between the plurality of first semiconductor layers and the narrow bandgap semiconductor layer. The values of overlap integrals between different electron wavefunctions in a conduction band of the chirp layer can be less than 0.05 for intersubband transition energies greater than 1.0 eV, and/or the values of overlaps between electron wavefunctions and barrier centers in a conduction band of the chirp layer can be less than 0.3 nm.sup.−1, when the structure is biased at an operating potential. The chirp layer can comprise a short-period superlattice with alternating wide bandgap barrier layers and narrow bandgap well layers, wherein the thickness of the barrier layers, or the well layers, or the thickness of both the barrier and well layers changes throughout the chirp layer.

A distributed feedback (DFB) laser outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The DFB laser includes a separate confinement heterostructure layer positioned between the quantum well active layer and then-type cladding layer. The DFB laser includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and then-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The DFB laser has a function to select a specific wavelength by returning a specific wavelength in the wavelength-variable laser.