Abstract: A semiconductor optical device, a fiber optical amplifier and an optical transmission system are disclosed. The semiconductor optical device is excellent in the stability of the coupling efficiency and the splitting ratio of a Y-branch. Both the fiber optical amplifier and the optical transmission system operate in a stable manner over a long period of time even if an optical waveguide is employed which is operative in a multi-mode in the transverse direction. The semiconductor optical device has an optical waveguide, a mode filter for transmitting therethrough light of a fundamental mode and blocking the propagation of light of a higher-order mode. The mode filter is provided in at least a part of the optical waveguide. The width of the mode filter is larger than that of the optical waveguide.

Abstract: In the structure of the device of the invention, a supper-lattice buffer layer is formed between the undoped layer and doped layers. This super-lattice buffer layer serves as a carrier-piling up layer in place of the undoped layer in the conventional device. Thus, the amounts of the piled-up carriers in the undoped layer can be greatly reduced and hence no band filling effect occurs in the undoped layer. Consequently, an optical device having a flat frequency characteristic can be produced without losing its modulating characteristic.

Abstract: A passive region is provided on one side or both sides of a waveguide-type optical modulator. Thereby, it is possible to obtain a high-speed optical modulator package superior in mechanical strength, thermal characteristic, high-frequency characteristic, and extinction characteristic. Moreover, it is possible to increase the operating speed of an optical fiber transmission equipment by applying the optical modulator package to the optical fiber transmission equipment.

Abstract: To obtain an optical functional device such that the reflectivity of a facet and the loss of coupling with a fiber are reduced, a mode conversion region for changing the beam spot size is formed on the input facet and/or the output facet in an optical function region and the facet of the side to be connected with a fiber in the mode conversion region is formed obliquely to the direction of propagation of light.

Abstract: Disclosed is a semiconductor optical integrated device and method of fabricating the device, the device having a plurality of quantum well structures, formed on a single substrate, acting as optical waveguides, the plurality of quantum well structures respectively having different lattice mismatches with the substrate and/or different strains (e.g., respectively compressive strain and tensile strain). The method includes selectively depositing the quantum well structures by, e.g., organometallic vapor phase epitaxy on growth regions of the substrate, the growth regions being defined by insulating layer patterning masks, with a width of the growth regions and/or a width of the patterning mask being different for the different quantum well structures.

Abstract: An optical signal is incident on a semiconductor optical waveguide with a grating and is reflected or transmitted therethrough to thereby perform dispersion compensation. Application of an electric field or implantation of carriers can be effected in the optical waveguide by means of electrodes attached in the optical waveguide. In addition, a temperature of the optical waveguide can be varied by a resistance heater. By using these measures, the dispersion compensation wavelength and the dispersion compensation intensity can be adjusted.

Abstract: An optical transmitter apparatus comprises a light source for optical signal transmission, an intensity modulator, a transmit signal generator and a signal generator. A transmit signal to be transmitted is supplied from the transmit signal generator to the intensity modulator, while a signal generated by the signal generator is supplied to the phase modulator. A light beam emitted from the light source passes through the intensity modulator and the phase modulator to be subsequently sent out as an optical signal for transmission with intensity thereof being modulated upon passing through the intensity modulator while spectrum thereof being spread by phase modulation which the optical signal undergoes upon passing through the phase modulator.

Abstract: There is provided a self-routing optical switch array formed by connecting m stages of optical switches and set so as to satisfy the relation:.lambda..sub.a1 <.lambda..sub.1 <.lambda..sub.a2 .lambda..sub.2 <. . . <.lambda..sub.an <.lambda..sub.n. . . <.lambda..sub.am <.lambda..sub.m <.lambda..sub.swhere .lambda..sub.n is wavelength of an absorption edge of a switching region of an nth stage of the optical switch array; .lambda..sub.an is wavelength of destination signal light multiplexed with information signal light used in an optical switch located at the nth stage, and .lambda..sub.s is wavelength of the information signal light.

Abstract: An optical modulator includes two cladding layers of different conductive types, a light absorption layer formed between the cladding layers for propagating incident light and for absorbing the light in response to a voltage applied between the cladding layers, and an optical waveguide layer formed between the cladding layers and optically connected to the light absorption layer, for propagating the light.

Abstract: An optical receiving method utilizing polarization diversity is disclosed in which first and second reference lightwaves having different frequencies and having polarization planes substantially perpendicular to each other, are combined with a signal lightwave to form a combined lightwave. The combined lightwave is subjected to heterodyne detection to obtain a detection signal and the detection signal is separated into first and second intermediate-frequency signals having different carrier frequencies. The first and second intermediate-frequency signals are converted into first and second baseband signals, respectively, and the first and second baseband signals are added to obtain an output signal.

Abstract: A waveguide type light merging and branching device, in which a resistance layer is disposed on a surface of a substrate or at least on one side therein and a low refractive index layer (refractive index n.sub.b), a core waveguide layer (refractive index n.sub.c, n.sub.c >n.sub.b), and a cladding layer (refractive index n.sub.n, n.sub.n >n.sub.c) superposed thereon on each other, the resistance layer having electrode terminals at the two extremities thereof, to which a voltage is applied.

Abstract: This invention relates to an optical multi/demultiplexer which will be useful for optical wavelength-division multiplexing communication using an optical fiber.In order to obtain high isolation, the optical multi/demultiplexer of the present invention constitutes three, mutually the same optical multi/demultiplexers by use of a main waveguide and first, second and third branch waveguides. Two rays of light having mutually different wavelenths, which are incident into the main waveguide, are isolated completely by the three optical multi/demultiplexers and are outputted.

Abstract: A waveguide type optical device in which a waveguide layer for propagating light is provided on the front surface of a substrate, and a compensation layer having a coefficient of thermal expansion substantially equal to that of the waveguide layer formed on the front surface is provided on the rear surface of the substrate.

Abstract: While a middle part of a plastic optical fiber bundle in a lengthwise direction thereof is being heated, it is twisted, and it is pulled in axial directions of the bundle. A biconically tapered portion is formed at the middle part of the bundle by the twisting and the pulling. When the biconically tapered portion has been formed into a predetermined shape, the heating is stopped, and simultaneously, a gas is blown against an outer periphery of the biconically tapered portion so as to rapidly cool this tapered portion. The biconically tapered portion is solidified to the predetermined shape by the rapid cooling.

Abstract: An optical filter is formed by providing a plurality of gaps, which have a desired width and such a depth that is larger than the thickness of the waveguide layer, in a slab or a waveguide layer in a three-dimensional optical waveguide so as to extend in the light propagating direction at desired period intervals. These gaps are filled with a film of a material, the refractive index of which is different from that of the waveguide layer, to complete the optical filter. A multiplex wavelength transmission device is formed monolithically by providing at least one optical filter, which is formed in the above-mentioned manner, in an optical waveguide, and arranging one or both of a light-emitting semiconductor element and a photodetector on the side of an optical signal which has passed through the optical filter, and on the side of an optical signal which has been reflected on the same optical filter.

Abstract: An optical multi/demultiplexer comprising a first waveguide for inputting/outputting light, second and third waveguides which are respectively arranged on both sides of the first waveguide, and first and second open-waveguides which are respectively arranged on sides of the second and third waveguides remote from the first waveguide.