Abstract: The semiconductor laser disclosed includes a first conductivity type buffer layer, an active layer and a second conductivity type cladding layer which are sequentially positioned on a first conductivity type semiconductor substrate. The active layer has a laser gain region to which an electric current is injected. The laser gain region having a width varying linearly along a resonating direction is disposed between a high reflection film provided on a facet of a wide side of the laser gain region of the active layer and a low reflection film provided on a facet of a narrow side of the laser gain region of the active layer. The facet of the narrow side is for outputting oscillation beams of a high order mode. This provides a high electrical-to-optical conversion efficiency, and enables the outputting of a large output from a narrow light emission region.

Abstract: In a well-known semiconductor laser, a multiple quantum well type active layer consisting of barrier layers and active layers or well layers, each of which has a thickness less than the de Broglie wavelength of electrons, is doped with an impurity, and the impurity density is made higher in the barrier layer than in the well layer. Further, in a case where the multiple quantum well active layer is held between p-type and n-type cladding layers, the well layer is undoped, the part of the barrier layer lying in contact with the well layer is undoped, and the other part of the barrier layer close to the p-type cladding layer is put into the n-conductivity type while that of the barrier layer close to the n-type cladding layer is put into the n-conductivity type. Desirably, the impurity density should range from about 1.times.10.sup.18 to about 1.times.10.sup.19 cm.sup.- 3.

Abstract: A semiconductor laser is disclosed in which a light emitting region having a light emitting layer and a waveguide region having a waveguide layer which is coupled to at least one side of the light emitting layer with a high efficiency are integrated on the same substrate; the light emitting region includes an active filter section having a diffraction grating equipped with a band-pass filter function; the light emitting region and the waveguide region are electrically isolated and are each provided with an electrode; and the oscillation wavelength of the semiconductor lase is changed by changing the refractive indices of at least the waveguide region and the active filter section through voltage application or current injection to the electrodes, thereby producing a narrow-linewidth, single-wavelength oscillation output light of a wavelength which corresponds to the transmission wavelength of the active filter section determined by the preset refractive indices of the waveguide region and the active filter se

Abstract: A solid state laser is disclosed wherein a semiconductor active layer is arranged in a Fabry-Perot cavity and the active layer is doped with a rare earth ion having a dominant emission wavelength. The proportion of elements for the compound active layer is chosen such that the bandgap corresponds to a wavelength which is longer than the emission wavelength of the rare earth ion. In the specific embodiment disclosed, the quarternary semiconductor compound is gallium indium arsenide phosphide and the rare earth ion is erbium.

Abstract: A semicondcutor laser comprises a semiconductor base structure provided with an etched channel, and a plurality of semiconductor layers laminated on the base structure by a liquid-phase epitaxial growth method and performing a laser function. The base structure includes a GaAs substrate of one conductivity type, a layer formed on the substrate for preventing deformation of the channel, and an oxidation-preventing layer formed on the channel deformation-preventing layer. A current-blocking layer consisting of GaAs of the opposite conductivity type may be formed between the GaAs substrate and the channel deformation-preventing layer. Further, another layer for preventing the channel deformation may be provided between the GaAs substrate and the current-blocking layer. In the invented semiconductor laser, the semiconductor layers are epitaxially grown sufficiently on the base structure, and the channel deformation can be sufficiently suppressed.