Abstract: An optical wavelength division multiplexing transmission network system having a star-topology network is disclosed, which comprises an arrayed-waveguide grating type multiplexing/demultiplexing circuit having N input ports and N output ports, and N transmitting/receiving apparatuses, each apparatus including a transmitter, receiver, demultiplexer, multiplexer, and N 2-input and 2-output optical path switching elements corresponding to N wavelengths, so as to cope with a damage to a transmitting or receiving portion corresponding to a specific wavelength. Each switching element is independently switched between first and second connective conditions.

Abstract: An optical signal processor according to the present invention is an optical circuit of a lattice configuration. Its basic circuit structure comprises 3 dB directional couplers, two optical waveguides with equal optical path lengths, and two optical waveguides with different optical path lengths (an optical path difference of about 1 to 50 mm). Phase controllers for performing phase shift are provided on the optical waveguides. The portions with equal optical path lengths function as variable directional couplers, and variable directional couplers having arbitrary coupling rates can be constructed by changing the phase controllers on the optical waveguides with equal optical path lengths. As for an adaptive filter, there is adopted a construction in which a photodetector for withdrawing part of output is provided at the output port, and a feedback electric wiring for feedback control is laid.

Abstract: An integrated optical waveguide circuit includes a substrate; an optical wavelength multiplexer and an optical power splitter formed on a same surface of the substrate. The optical wavelength multiplexer is composed of a first slab optical waveguide, a second slab optical waveguide, a single or a plurality of input optical waveguides connected to the first slab optical waveguide at one end of the first slab optical waveguide, a plurality of arrayed optical waveguides arranged in parallel and having different lengths and connected to the first slab optical waveguide and the second slab optical waveguide, and a plurality of output optical waveguides arranged in parallel and connected to the second slab optical waveguide. The optical power splitter is composed of the second slab optical waveguide, one or more input optical waveguides, and the plurality of output optical waveguides arranged in parallel and connected to the second slab optical waveguide.

Abstract: An optical switching module has an optical waveguide substrate mounted on an electronic circuit substrate. According to a first aspect of the invention, the optical waveguide substrate has thin-film heaters, and the electronic circuit substrate has trimmable thick-film resistors for adjusting current fed to the thin-film heaters. According to a second aspect of the invention, the optical switching module also has a pair of fiber pigtails butt-coupled to the optical waveguide substrate. The fiber pigtails are secured to the ends of a supporter, which is attached to a heat sink fastened below the electronic circuit substrate. According to a third aspect of the invention, the optical waveguide substrate is mounted in a depression in the electronic circuit substrate. The invention reduces the size of the optical switching module.

Abstract: An optical device is presented which is useful for optical signal transmission and switching systems by multiplexing and demultiplexing optical signals in looped optical paths, consisting of a plurality of individual loop-back optical paths. The device is essentially a multi/demultiplexer having an arrayed waveguide grating disposed between a plurality of input sections and output sections which are joined by the plurality of individual loop-back optical paths. Because the modulated signals are looped back into the same optical paths using the same devices, problems of mismatching performance introduced by using different optical devices are avoided. The device processes individual optical signals of different wavelengths, minimizes splitting losses, and reduces noise components by producing narrow bandpass signals of high signal to noise ratio. Optical signal splitting and insertion, delay line memory and delay equalization circuits can all be handled by the same circuit configuration.

Abstract: A waveguide-type optical matrix switch including as its switching element a Mach-Zehnder interferometer which includes two directional couplers and an optical phase shifter. The two directional couplers are arranged by placing two optical waveguides in close proximity at two positions on a substrate, and have an identical coupling ratio. The optical phase shifter is disposed over at least one of the two optical waveguides between the directional couplers. The two optical waveguides have an effective optical path length difference of half a wavelength of a light signal between the two directional couplers, and are intersected in the optical switch element. The waveguide-type optical matrix switch is little affected by fabrication errors in the coupling ratio of the directional couplers, and superior in the extinction ratio.

Abstract: In an optical MDF (main distributing frame) for interconnecting external subscriber optical lines (122) with office optical lines (131) through jumpering operation, a matrix waveguide (128, 129, 130) having a plurality of crosspoints coupled with external lines and office lines is used. The matrix waveguide has a groove (235 in FIG. 4A) at each crosspoint so that said crosspoint is switched ON or OFF depending upon whether said groove is filled with matching oil or not, so that one of the external lines is connected to the selected office line. Said matching oil has the same refractive index as that of waveguides. Each crosspoint groove is coupled with a respective oil pool (236), which supplies matching oil which has essentially the same refractive index as that of a waveguide to said groove.

Abstract: A guided-wave optical branching device having optical waveguides disposed on a substrate. The waveguides are partially arranged to be close to each other to form a tapered directional coupler in which the waveguides are point symmetrical or line symmetrical. Alternatively, the waveguides are neither line symmetrical nor point symmetrical. The tapered directional coupler reduces the wavelength dependence of the coupling ratio of the output power derived from the branching device. The widths of the waveguides in the parallel coupling region, the length of the coupling region in the symmetrical or asymmetrical directional coupler, the asymmetrical parameters or the like are set at values determined in accordance with the wavelength range used, so that the wavelength dependence of the coupling ratio of the power between the input port and the output port is reduced in a desired wavelength range, for example, 1.2 .mu.m-1.8 .mu.m.

Abstract: A method for adjusting a characteristic of a guided-wave optical circuit which includes one or more waveguides formed by a substrate, a cladding layer formed on the substrate, and a core portion having one or more cores embedded in the cladding layer. The method is carried out by producing a reversible thermal hysteresis phenomenon, after the clading layer and core portion have been formed. The thermal hysteresis phenomenon is produced in a thermal hysteresis produced region preselected so as to include at least a portion of the cladding layer and/or the core portion, thereby adjusting a refractive index difference between the cladding layer and the core portion.

Abstract: A guided-wave optical branching component is composed of a Mach-Zehnder interferometer having two or more directional couplers. A slight difference .DELTA.L in the optical-path length is provided in two or more optical waveguides connecting the two or more directional couplers. The difference of the optical-path length is less than the shortest wavelength in the operational wavelength region of the guided-wave optical branching component, and the coupling ratio of each of the two directional couplers monotonically increases with wavelength in the operational wavelength region. By using the optical branching components thus constructed (i.e., Mach-Zehnder interferometer type 3-dB optical coupler) in conjunction with a phase shifter, a Mach-Zehnder interferometer type optical switch can be achieved.

Abstract: An integrated optical device includes a substrate; a single-mode optical waveguide having a cladding layer disposed on the substrate and a core portion embedded in the cladding layer for transmitting light therethrough; and a stress applying film disposed on a desired portion of the cladding layer for adjusting stress-induced birefringence of the single-mode optical waveguide by irreversibly changing the stress exerted on the core portion by a trimming technique. The integrated optical device can be manufactured by the steps of forming a cladding layer on a substrate; forming a single-mode optical waveguide having a core portion embedded in the cladding layer for transmitting light therethrough; and forming, on the cladding layer, a stress applying film for exerting a stress on the single-mode optical waveguide to irreversibly change the stress by trimming the film.

Abstract: An integrated optical device includes a substrate; a single-mode optical waveguide having a cladding layer disposed on the substrate and a core portion embedded in the cladding layer for transmitting light therethrough; and a stress applying film disposed on a desired portion of the cladding layer for adjusting stress-induced birefringence of the single-mode optical waveguide by irreversibly changing the stress exerted on the core portion by a trimming technique. The integrated optical device can be manufactured by the steps of forming a cladding layer on a substrate; forming a single-mode optical waveguide having a core portion embedded in the cladding layer for transmitting light therethrough; and forming, on the cladding layer, a stress applying film for exerting a stress on the single-mode optical waveguide to irreversibly change the stress by trimming the film.

Abstract: A single-polarization single-mode optical fiber comprises a core made of silica glass, a clad surrounding the core and made of silica glass having a smaller index of refraction than the glass comprising the core, a pair of stress applying members symmetrically disposed on the clad and made of silica glass having different thermal expansion coefficient from that of the clad, spacers interposed between the stress applying members and made of silica glass having substantially the same thermal expansion coefficient as the clad, and a jacket surrounding the spacers, stress applying members. The jacket is also made of silica glass and has a smaller expansion coefficient than the stress applying members. The optical fiber of this invention has an excellent polarization preserving characteristic, low loss, long length, and stable characteristics.

Abstract: In a single mode optical waveguide having a substrate, a cladding layer formed on the substrate, a core portion embedded in the cladding layer, and an elongated member for applying a stress to the core portion or a stress relief groove for relieving a stress from the core portion in the cladding layer along the core portion. The position, shape and material of the elongated member or the groove are determined in such a way that stress-induced birefringence produced in the core portion in accordance with a difference in thermal expansion coefficient between the substrate and the single mode optical waveguide is a desired value.

Abstract: An optical coupler for single mode optical signals having a tunable (variable) coupling ratio, and a method of fabricating the coupler. A pair of virtually identical optical fibers are fused together at a narrowed waist region, each fiber being formed of a core and cladding, each being tapered toward the waist in such a manner as to ensure adiabatic propagation of light in the structure. An optical signal carried by one fiber first passes through a decreasing taper region and then passes through an increasing taper region of one or the other fiber (or both). The decreasing taper rate of the input portion of one fiber is such that the optical signal radiates out of the core (where V=1 locally) and into the cladding, as it approaches the waist. The increasing taper rates of the output portions of the two fibers are such that a predetermined coupling ratio is obtained.

Abstract: A hybrid optical integrated circuit having a high-silica glass optical waveguide formed on a silicon substrate, an optical fiber and an optical device coupled optically to the optical waveguide, and an optical fiber guide and an optical device guide on the substrate for aligning the optical fiber and the optical device at predetermining positions, respectively, relative to the optical waveguide. Islands carrying electrical conductors are disposed on the substrate. A first electrical conductor film is formed on the substrate. Second electrical conductor films are formed on the top surfaces of the optical waveguide, the optical fiber guide, the optical device guide and the islands and are electrically isolated from the first electrical conductor film. An electrical conductor member is provided to feed electric power from the first and second electric conductor films to the optical device which needs the power supply.

Abstract: A method for fabricating a hybrid optical integrated circuit having a high-silica glass optical waveguide formed on a silicon substrate, an optical fiber and an optical device coupled optically to the optical waveguide, and an optical fiber guide and an optical device guide on the substrate for aligning the optical fiber and the optical device at predetermined positions, respectively, relative to the optical waveguide. Islands carrying electrical conductors are disposed on the substrate. A first electrical conductor film is formed on the substrate. Second electrical conductor films are formed on the top surfaces of the optical waveguide, the optical fiber guide, the optical device guide and the islands and are electrically isolated from the first electrical conductor film. An electrical conductor member is provided to feed electric power from the first and second electric conductor films to the optical device which needs the power supply.

Abstract: A core torch for fabricating a single-mode optical fiber preform wherein fine glass particles are produced eccentrically with respect to the center area of a flame stream, the core torch being so arranged as to blow the flame stream at an angle inclined to a seed rod. The porous glass body forming the core is grown on one end of the rod and in the direction of the axis of the rod. A cladding layer is formed on the periphery of the porous glass core body by at least one torch for forming the cladding. The obtained porous glass body is heated and vitrified into a transparent glass body, which is sealed in a silica tube for jacketting to form a single-mode optical fiber preform. At least one exhaust port is disposed within a distance of 1 mm to 50 mm from the periphery of the porous glass body and in the vicinity of the growing surface of the glass body to exhaust residual glass fine particles and undesired gases. A porous glass body having a diameter of 20 mm or less is easily formed.

Abstract: A method of fabricating an optical fiber preform wherein a synthesizing torch is inclined between 10.degree. and 60.degree. with respect to the rotation axis of a seed rod. Moving the rod while rotating it, a glass raw material gas and a flame forming gas are blown out individually from the torch to synthesize glass particles which are deposited onto one end of the rod, so that a cylindrical porous preform is grown in the direction of the rotation axis of the rod. Then the porous preform is heated at a high temperature to vitrify the porous preform into a transparent optical fiber preform. At least one exhaust port is disposed at a distance of 1 mm to 50 mm from the periphery of the porous preform and in the vicinity of the growing surface of the porous preform. In fabricating the porous preform the outer diameter fluctuations are small, and the preform is formed stably without formation of cracking on the periphery of the preform.

Abstract: A method of fabricating a single-mode optical fiber preform wherein a core torch produces fine glass particles eccentrically with respect to the center area of a flame stream, the core torch being so arranged as to blow the flame stream at an angle inclined to a seed rod. The porous glass body forming the core is grown on one end of the rod and in the direction of the axis of the rod. A cladding layer is formed on the periphery of the porous glass core body by at least one torch for forming the cladding. The obtained porous glass body is heated and vitrified into a transparent glass body, which is sealed in a silica tube for jacketting to form a single-mode optical fiber preform. At least one exhaust port is disposed within a distance of 1 mm to 50 mm from the periphery of the porous glass body and in the vicinity of the growing surface of the glass body to exhaust residual glass fine particles and undesired gases. A porous glass body having a diameter of 20 mm or less is easily formed.