A QCL includes a semiconductor substrate and an active layer provided on the semiconductor substrate. The active layer has a cascade structure in which a unit laminate including a light emission layer which generates light and an injection layer to which electrons are transported from the light emission layer is laminated in multiple stages. The light emission layer and the injection layer each have a quantum well structure in which quantum well layers and barrier layers are alternately laminated. A separation layer including a separation quantum well layer having a layer thickness smaller than an average layer thickness of the quantum well layers included in the light emission layer and smaller than an average layer thickness of the quantum well layers included in the injection layer is provided between the light emission layer and the injection layer in the unit laminate.

Provided is a quarter-wavelength shifted distributed feedback laser diode. The laser diode includes a substrate having a laser diode section and a phase adjustment section, a waveguide layer on the substrate, a clad layer on the waveguide layer, a grating disposed in the clad layer in the laser diode section, an anti-reflection coating disposed on one side walls, of the substrate, the waveguide layer, and the clad layer, adjacent to the laser diode section, and a high reflection coating disposed on the other side walls, of the substrate, the waveguide layer, and the clad layer, adjacent to the phase adjustment section.

The grating layer of a surface emitting laser is divided into a first grating region and a second grating region along a horizontal direction. The second grating region is located at a middle area of the grating layer, while the first grating region is located in an outer peripheral area of the grating layer. Each of the first and second grating regions comprises a plurality of micro-grating structures. The grating period of the micro-grating structures in the first grating region is in accordance with the following mathematical formula:

[00001]$.Math.=m\frac{}{2*n_{\mathrm{eff}}};$

in addition, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula:

[00002]$.Math.=o\frac{}{2*n_{\mathrm{eff}}}.$

Wherein, is the length of grating period, is the wavelength of the laser light, n.sub.eff is the equivalent refractive index of semiconductor waveguide, m=1, and o=2. The first grating region is a first-order grating region, and the second grating region is a second-order grating region, so as to form a hybrid grating structure in the grating layer. The surface emitting laser emits laser light perpendicularly from a light-emitting surface defined by the second grating region.

A distributed reflector (DR) laser may include a distributed feedback (DFB) region and a distributed Bragg reflector (DBR). The DFB region may have a length in a range from 30 micrometers (m) to 100 m and may include a DFB grating with a first kappa in a range from 100 cm.sup.1 to 150 cm.sup.1. The DBR region may be coupled end to end with the DFB region and may have a length in a range from 30-300 m. The DBR region may include a DBR grating with a second kappa in a range from 150 cm.sup.1 to 200 cm.sup.1. The DR laser may additionally include a lasing mode and a p-p resonance frequency. The lasing mode may be at a long wavelength side of a peak of a DBR reflection profile of the DBR region. The p-p resonance frequency may be less than or equal to 70 GHz.

A semiconductor laser device is a vernier-type wavelength-tunable semiconductor laser device including an optical resonator, constituted by first and second reflective elements having reflection comb spectra in which reflection peaks are arranged on a wavelength axis in a substantially periodic manner and having mutually different periods. At least one of the first and second reflective elements has a sampled grating structure having a reflection comb spectrum in which reflection phases at the respective reflection peaks are aligned and the intensity of a reflection peak outside a set laser emission wavelength bandwidth is lower than the intensity of a reflection peak within the laser emission wavelength bandwidth.

A distributed feedback (DFB) semiconductor laser device includes an active layer, a first grating layer and a second grating. The first grating layer has a first grating structure with a first grating period. The second grating layer has a second grating structure with a second grating period substantially different from the first grating period. The active layer, the first grating layer and the second grating layer are vertically stacked, and the equivalent grating period of the DFB semiconductor laser device is (2P1P2)/(P1+P2), where P1 and P2 respectively represent the first grating period and the second grating period.

To provide a two-dimensional photonic crystal surface emitting laser capable of improving characteristics of light to be emitted, in particular, optical output power. The two-dimensional photonic crystal surface emitting laser includes: a two-dimensional photonic crystal including a plate-shaped base member and modified refractive index regions where the modified refractive index regions have a refractive index different from that of the plate-shaped base member and are two-dimensionally and periodically arranged in the base member; an active layer provided on one side of the two-dimensional photonic crystal; and a first electrode and a second electrode provided sandwiching the two-dimensional photonic crystal and the active layer for supplying current to the active layer, where the second electrode covers a region equal to or wider than the first electrode.

A surface-emitting laser, which is a ridge waveguide structure, including: a substrate, a first cladding layer, an active layer, a conductive layer, a second cladding layer; the Bragg gratings is etched on the surface of the ridge waveguide; the two upper electrodes are disposed on both sides of the ridge waveguide; two grooves are formed between the ridge waveguide and each of the two upper electrodes; the first waveguide cladding layer includes one or more current confinement regions; or a buried tunnel junction is formed in the second cladding layer for limiting current. The Bragg gratings comprise two first-order gratings and one second-order grating placed between two first-order gratings.

A Distributed Feedback Laser (DFB) mounted on a Silicon Photonic Integrated Circuit (Si PIC), the DFB having a longitudinal length which extends from a first end of the DFB laser to a second end of the DFB laser, the DFB laser comprising: an epi stack, the epi stack comprising: one or more active material layers; a layer comprising a partial grating, the partial grating extending from the second end of the DFB laser, only partially along the longitudinal length of the DFB laser such that it does not extend to the first end of the DFB laser; a highly reflective medium located at the first end of the DFB laser; and a back facet located at the second end of the DFB laser.

A disclosed semiconductor laser device includes a distributed feedback portion serving as a light-emittable active region the distributed feedback portion having a diffraction grating; and a distributed reflective portion serving as a passive reflective mirror, the distributed reflective portion having a diffraction grating, wherein the distributed feedback portion includes a first region adjacent to the distributed reflective portion and having a diffraction grating having a predetermined standard period, a phase shift region adjacent to the first region, the phase shift region being longer by twice or more than the standard period, and a second region adjacent to an opposite side to the first region of the phase shift region and having a diffraction grating with the standard period, and the phase shift region optically changes a phase of laser beam between the first region and the second region.