A distributed feedback plus reflection (DFB+R) laser includes an active section, a passive section, a low reflection (LR) mirror, and an etalon. The active section includes a distributed feedback (DFB) grating and is configured to operate in a lasing mode. The passive section is coupled end to end with the active section. The LR mirror is formed on or in the passive section. The etalon includes a portion of the DFB grating, the passive section, and the LR mirror. The lasing mode of the active section is aligned to a long wavelength edge of a reflection peak of the etalon.

A semiconductor laser array includes: a plurality of semiconductor lasers configured to oscillate in a single mode at oscillation wavelengths different from one another, each semiconductor laser including an active layer including a multi-quantum well structure including a plurality of will layers and a plurality of barrier layers laminated alternately, and an n-side separate confinement heterostructure layer and p-side separate confinement heterostructure layer configured to sandwich the active layer therebetween in a thickness direction, band gap energies of the n-side separate confinement heterostructure layer and the p-side separate confinement heterostructure layer being greater than band gap energies of the barrier layers of the active layer. The active layer is doped with an n-type impurity.

A nitride light emitter includes: a nitride semiconductor light-emitting element including an Al.sub.xGa.sub.1-xN substrate (0≤x≤1) and a multilayer structure above the Al.sub.xGa.sub.1-xN substrate; and a submount substrate on which the nitride semiconductor light-emitting element is mounted. The multilayer structure includes a first clad layer of a first conductivity type, a first light guide layer, a quantum-well active layer, a second light guide layer, and a second clad layer of a second conductivity type which are stacked sequentially from the Al.sub.xGa.sub.1-xN substrate. The multilayer structure and submount substrate are opposed to each other. The submount substrate comprises diamond. The nitride semiconductor light-emitting element has a concave warp on a surface closer to the Al.sub.xGa.sub.1-xN substrate.

A laser device (100), comprising: a source of electromagnetic radiation (S) that comprises at least one reflecting surface (RS), said source (S) being configured to generate a light beam that follows an optical path (OPa; OP) external to said source (S); a dispersive stage (6) located outside said source (S) along said optical path (OP) of said light beam generated by said source (S), said dispersive stage (6) comprising at least one axis of reflection that forms an angle (Θ; cp) with said optical path (OPa; OP) of said light beam and being configured to reflect: at least a first spectral portion of said light beam generated by said source (S) towards said source (S); and a second spectral portion of said light generated by the source (S) along said axis of reflection, wherein said at least one reflecting surface (RS) and said dispersive stage (6) form at least one variable-length external optical cavity (RS, L, 6); at least one collimating lens (C) located along said optical path (OPa; OP) and configured to collimate said light beam coming from said source (S); a collimator module (3), in which said source (S) and said at least one collimating lens (C) are mounted; and an actuator (24) configured to vary a length (L) of said a variable-length external optical cavity (RS, L, 6). In said device: said actuator (24) is mechanically coupled to said collimator module (3); and said actuator (24) is configured to vary the length (L) of said at least one external optical cavity of the variable-length gain medium (RS, L, 6) by moving said collimator (3).

Aspects of the present disclosure describe systems, methods and structures including an integrated-optics-based externa-cavity laser configured for mode-hop-free wavelength tuning having an increased continuous tuning range with an ultra-narrow linewidth by increasing tuning sensitivity. Ultra-narrow linewidth is provided by extending cavity length with a multi-pass resonator based filter that may advantageously include tunable microring resonators that enable single-mode oscillation while contributing to the optical length of the laser with multiple passes of light through the ring(s) per roundtrip in the laser cavity. Further aspects of the present disclosure describe systems, methods, and structures exhibiting an enhanced “tuning sensitivity”—defined by a continuous wavelength shift per induced cavity phase shift by a phase section. Such tuning sensitivity is increased by approximately a factor of 3 for synchronous tuning of phase section and ring resonators as compared to tuning phase section only.

A semiconductor optical device in which a light emitting region that emits light and a reflecting region that reflects the light to the light emitting region side are integrated includes a core layer that is provided in the light emitting region, and a waveguide layer that is provided in the reflecting region, that is optically coupled to the core layer, and that has a band gap that is larger than energy of the light. The reflecting region has a first thyristor that overlaps the waveguide layer in a direction that intersects a propagation direction of the light.

A laser comprising a laser cavity formed by a first optical reflector, a gain region, a second optical reflector having a plurality of reflection peaks, and at least one optically active region. The first mirror may be a DBR or comb mirror and the second mirror may be a comb mirror. The spectral reflectance of the second optical reflector is adjusted at least partially based on an electric signal received form the optically active region such that only one reflection peak is aligned with a cavity mode formed by the first and second reflector.

A light-emitting device includes: a light source including plural light-emitting elements; a first optical member that is provided in a light-emitting path of the light source, the first optical member being configured to reduce intensity of light emitted from the light source and emit the light; and a second optical member that is provided on a light-emitting side of the first optical member and is configured to diffuse and irradiate light incident from the first optical member.

A quantum cascade laser element includes: a semiconductor substrate; a semiconductor laminate including an active layer and having a first end surface and a second end surface facing each other in an optical waveguide direction; a first electrode; a second electrode; and an anti-reflection film formed on the first end surface. The semiconductor laminate is configured to oscillate laser light having a central wavelength of 7.5 μm or more. The anti-reflection film includes at least one of at least one layer of a CeO.sub.2 film formed by continuous sputtering and vacuum evaporation and a plurality of layers of CeO.sub.2 films formed by discrete sputtering and vacuum evaporation.

A tunable laser system includes a laser diode producing a light beam having a plurality of frequencies in a visible portion of a light spectrum. A collimating lens arranged in front of the laser diode produces a collimated light beam from the light beam produced by the laser diode. A partial reflector arranged in a path of the collimated laser beam reflects a first portion of the collimated light beam and passes a second portion of the collimated light beam as an output light beam. The first portion of the collimated light beam enters the laser diode and mixes with the plurality of frequencies of the light beam produced by the laser diode so that the laser diode produces a self-injection-locked light beam including at least two frequencies having a frequency difference in a terahertz frequency range. A translational stage adjusts a distance between the laser diode and the partial reflector. The laser diode or the partial reflector is mounted on the translational stage. The at least two frequencies of the self-injection-locked light beam are based on the distance between the laser diode and the partial reflector.