A quantum cascade laser device includes a substrate, a semiconductor stacked body and a first electrode. The semiconductor stacked body includes an active layer and a first clad layer. The active layer is configured to emit infrared laser light by an intersubband optical transition. A ridge waveguide is provided in the semiconductor stacked body. A distributed feedback region is provided along a first straight line. The ridge waveguide extends along the first straight line. The first electrode is provided at an upper surface of the distributed feedback region. A diffraction grating is arranged along the first straight line. The distributed feedback region includes a an increasing region where a length of the diffraction grating along a direction orthogonal to the first straight line increases from one end portion of the distributed feedback region toward another end portion of the distributed feedback region.

A laser including: a gain chip; an external cavity incorporating a Bragg grating; and a baseplate; wherein a first end of the gain chip has a high reflectivity facet forming a first end of the laser cavity; a second end of the gain chip has a low reflectivity facet; and a second part of the external cavity comprises a Bragg grating, supported by the baseplate, the temperature of the baseplate being maintained through a feedback loop; wherein the optical length of the external cavity is at least an order of magnitude greater than the optical length of the gain chip; wherein the Bragg grating is physically long and occupies a majority of the length of the external cavity and is apodized to control the sidemodes of the grating reflection.

Waveguide Bragg gratings, optical reflectors and lasers including optical reflectors are disclosed. The optical reflectors include a waveguide, perturbations proximate to the waveguide to create a Bragg grating in the waveguide, and a DC index control structure positioned to vary the DC index along at least a portion of the Bragg grating. In laser embodiments, the waveguide may be coupled to the second end of a semiconductor gain element to form an external cavity having an optical length and a cavity phase. The gain element and optical reflector may be monolithically integrated on a substrate or separate structures.

In a distributed feedback semiconductor laser element, a multi-layered structure includes a GaN substrate, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, and a ridge waveguide is formed. A first diffraction grating is formed adjacent to and on both sides of the ridge waveguide. A depth d of a groove of the first diffraction grating is included in the range of 50 nm d200 nm, and a duty ratio duty is included in the range of an inequality (1) using constants a, b, c, and n defined for the order of the diffracted light.

[00001]$\begin{array}{cc}-\sqrt[n]{\frac{d-c}{a}}+b\mathrm{duty}\sqrt[n]{\frac{d-c}{a}}+b& \left(1\right)\end{array}$

An optical device includes an active layer disposed over a semiconductor substrate, a diffraction grating disposed over the active layer, a clad layer partly disposed over the diffraction grating, at least one first burying material layer disposed beside side surfaces of end portions of the clad layer over the diffraction grating, and at least one second burying material layer disposed beside side surfaces of a center portion of the clad layer over the diffraction grating. A refractive index of the at least one first burying material layer is different from a refractive index of the at least are second burying material layer.

A tunable laser device comprises a multi-section distributed feedback (DFB) laser having a first Bragg section including a waveguide and a Bragg grating, a second Bragg section comprising a waveguide and a Bragg grating, and a phase section being longitudinally located between the first Bragg section and the second Bragg section. The phase section is made of a passive material, and each Bragg section has a first longitudinal end joining the phase section and a second longitudinal end opposed to the phase section. The Bragg grating of at least one Bragg section has a grating coupling coefficient which decreases from the first longitudinal end to the second longitudinal end of the at least one Bragg section.

A method for producing a quantum cascade laser includes the steps of forming a laser structure including a mesa structure and a buried region embedding the mesa structure; forming a mask on the laser structure, the mask including a first pattern that defines a /4 period distribution Bragg reflector structure and a second pattern that defines a 3/4 period distribution Bragg reflector structure; and forming a first distribution Bragg reflector structure, a second distribution Bragg reflector structure, and a semiconductor waveguide structure by dry-etching the laser structure through the mask, the semiconductor waveguide structure including the mesa structure that has first and second end facets. The first distribution Bragg reflector structure is optically coupled to the first end facet. The second distribution Bragg reflector structure is optically coupled to the second end facet. Here, denotes a value of an oscillation wavelength of the quantum cascade laser in vacuum.

An optical device includes an active layer disposed over a semiconductor substrate, a diffraction grating disposed over the active layer, a clad layer partly disposed over the diffraction grating, at least one first burying material layer disposed beside side surfaces of end portions of the clad layer over the diffraction grating, and at least one second burying material layer disposed beside side surfaces of a center portion of the clad layer over the diffraction grating. A refractive index of the at least one first burying material layer is different from a refractive index of the at least are second burying material layer.