Abstract: An optical functional device equivalent to a 2×2 Mach-Zehnder optical switch is produced by forming two 3 dB couplers and input/output waveguides on a substrate. Two optical phase modulation paths are formed on corresponding waveguides between 3 dB couplers. A channel region having an opposite electric polarity is formed between source and drain regions, having the predetermined electric polarity, formed on the substrate. The optical phase modulation path is insulated from the surrounding area and disposed above the channel region. Additionally, a control electrode (i.e. a gate region) subjected to high-density doping is formed above the optical phase modulation path. By applying an electric voltage having the predetermined polarity to the control electrode, the source region, and the drain region, it is possible to generate hot carriers, in proximity to the optical phase modulation path, so as to accumulate charges and change a refractive index, thus setting a desired light-wave input/output path.

Abstract: A light source circuit transmits light incident from a semiconductor laser source to a plurality of optical devices. At least one optical branch section is formed to branch one input-side optical waveguide at least into a first output-side optical waveguide terminal and a second output-side optical waveguide terminal. A light path length (L1) between the optical branch section and a next-stage optical branch section or the optical device is connected to the first output-side optical waveguide extending from the optical branch section and a light path length (L2) between the optical branch section and the next-stage optical branch section selected such that the absolute value of a difference between (L1) and (L2) is (¼+i/2) times (i is zero or a positive integer) the wavelength of the light transmitted through the light source circuit.

Abstract: An optical semiconductor device includes a silicon oxide layer configured to be formed on a substrate; an optical waveguide part configured to be formed on the silicon oxide layer; a cladding layer configured to be formed covering the optical waveguide part; and a semiconductor laser configured to be disposed on the substrate. Laser light emitted from the semiconductor laser enters the optical waveguide part. The optical waveguide part increases transmittance of light when the wavelength becomes greater within an oscillation wavelength range of the semiconductor laser.

Abstract: The invention relates to a spot-size converter, a manufacturing method thereof, and an integrated optical circuit device, and ensures easier coupling to the optical fiber and higher accuracy in manufacturing the spot-size converter. A first core that is extended from a first end configured to input/output light toward a second end, and a second core that is formed by a plurality of cores, and formed at a position to be evanescent-coupled to the first core, and moreover extended along a direction from the first end toward the second end are provided, and, on the second core, a third core that has a taper unit and is formed at a position to be evanescent-coupled to the second core in a lamination direction is provided.

Abstract: An optical waveguide includes a substrate, a first core provided over the substrate and having a first taper region that extends from one side toward the other side and has a sectional area that decreases toward the other side, and a plurality of second cores provided over the substrate and over or under the first core with a first cladding layer sandwiched therebetween and extending in parallel to the substrate and the first core.

Abstract: A spot-size converter includes a substrate, a first core provided over the substrate, and second and third cores provided over the substrate and over or under the first core with a cladding layer sandwiched therebetween and extending in parallel to the substrate and the first core.

Abstract: In order to provide a spot size converter and a method for making the same which enable the optical connection with low loss and are able to reduce the excess loss for the position misalignment in mounting, a spot size converter according to an exemplary aspect of the present invention includes: a substrate on which an optical waveguide including a first core is laminated and which includes a notch; a core reducing part which is formed so that a cross-section area of the first core may gradually decrease toward an end part of the first core in the direction of light propagation; a second core which surrounds the core reducing part and is made of a material whose refractive index is smaller than that of the first core; a peripheral clad which surrounds the second core and is made of a material whose refractive index is smaller than that of the second core; and a lower clad which is formed in a lower part of the second core and includes the peripheral clad; wherein the lower clad is formed in the notch.

Abstract: An optical semiconductor device includes: a substrate of semiconductor; an array having a plurality of active regions arranged on the substrate so as to emit light to the same direction, the plurality of active regions being arranged more densely at ends of the array than in the center of the array in a direction crossing the light emitting direction; and electrodes which inject current to the plurality of active regions.

Abstract: An optical device includes: a first cladding layer; a core layer disposed on the first cladding layer and, with increase in its sectional area, extending from a first end which receives/outputs light along a direction from the first end toward a second end; a slab layer disposed on the first cladding layer and extending to the second end along the direction from the first end toward the second end; a rib layer disposed on the slab layer and, with decrease in its sectional area, extending to the second end along the direction from the first end toward the second end; and a second cladding layer disposed on the core layer and the rib layer. The core layer and both of the slab and rib layers are optically coupled in a part in which the sectional are of the core and rib layers is the maximum.

Abstract: A wavelength-variable light source according to the present invention includes 2×2 3-dB directional coupler 3, closed loop-type optical circuit 5, at least two resonators 1 and 2, and optical amplifier 4. The closed loop-type optical circuit 5 is formed by connecting ends of the two output paths of 3-dB directional coupler 3. The resonators 1 and 2 have different resonance wavelength periods. One end of optical amplifier 4 is optically connected to one input path end 6 of 3-dB directional coupler 3. Lasing light is output from the other end of the optical amplifier 4. A non-reflecting structure is formed at the other input path end 7 of the 3-dB directional coupler. The wavelength-variable light source configured as described above includes an element configured to vary the resonance wavelength of the resonator 1 or 2.

Abstract: Provided are an optical waveguide and a production method thereof which can constrict both the width and thickness of the SOI optical waveguide core layer in the same process and at the same time, simplify production process, and reduce optical losses. An optical waveguide includes a first clad layer formed on a semiconductor substrate; a first core layer formed on the upper side of the first clad layer with the use of a semiconductor material the refractive index of which is higher than that of the first clad layer; and a second clad layer formed on the upper side of the first core layer with the use of a material the refractive index of which is lower than that of the first core layer. The width of the first core layer is defined based on the width of an unoxidized semiconductor material sandwiched between oxide films the parts of which are thermally oxidized.

Abstract: A wavelength-variable light source according to the present invention includes 2×2 3-dB directional coupler 3, closed loop-type optical circuit 5, at least two resonators 1 and 2, and optical amplifier 4. The closed loop-type optical circuit 5 is formed by connecting ends of the two output paths of 3-dB directional coupler 3. The resonators 1 and 2 have different resonance wavelength periods. One end of optical amplifier 4 is optically connected to one input path end 6 of 3-dB directional coupler 3. Lasing light is output from the other end of the optical amplifier 4. A non-reflecting structure is formed at the other input path end 7 of the 3-dB directional coupler. The wavelength-variable light source configured as described above includes an element configured to vary the resonance wavelength of the resonator 1 or 2.

Abstract: Provided are an optical waveguide and a production method thereof which can constrict both the width and thickness of the SOI optical waveguide core layer in the same process and at the same time, simplify production process, and reduce optical losses. An optical waveguide includes a first clad layer formed on a semiconductor substrate; a first core layer formed on the upper side of the first clad layer with the use of a semiconductor material the refractive index of which is higher than that of the first clad layer; and a second clad layer formed on the upper side of the first core layer with the use of a material the refractive index of which is lower than that of the first core layer. The width of the first core layer is defined based on the width of an unoxidized semiconductor material sandwiched between oxide films the parts of which are thermally oxidized.

Abstract: Arranged for at least one of a pair of branch optical waveguides in a Mach-Zehnder type interference optical system is a ring resonance type phase shifter for modulating a light wave signal propagating through the branch optical waveguide. The ring resonance type phase shifter includes a ring-type optical waveguide arranged so as to be mode-coupled with the corresponding branch optical waveguide, and is configured so that amplitude branching ratio K between the corresponding branch optical waveguide and the ring-type optical waveguide can be varied with a change in refractive index or the like, accompanied by voltage application to a pn junction, for example. As amplitude branching ratio K is varied, the phase difference between the light wave signals propagating through the paired optical waveguides varies, to thereby control the intensity of the light wave signal output from the interference optical system.

Abstract: An optical switch not having waveguide crossings, as in a matrix switch, enabling input/output path switching of N×N, and not increasing the optical loss or the size when the number of channels increases. The optical switch includes plural input ports 10 and plural output ports 17 and has a path switching function of the planar waveguide type. The input ports are connected to one ends of respective different sub-slab optical waveguides 12. The opposite side ends of the sub-slab optical waveguides 12 are optically coupled to one end of a common main slab optical waveguide 15 via arrayed optical waveguides 14. To the opposite side end of the main slab optical waveguide 15 are connected plural output ports 17. On the top of the arrayed optical waveguides 14, there are respectively arranged electrodes 13, each causing the difference in the refractive index of the respective optical waveguide.

Abstract: An optical switch not having waveguide crossings, as in a matrix switch, enabling input/output path switching of N×N, and not increasing the optical loss or the size when the number of channels increases. The optical switch includes plural input ports 10 and plural output ports 17 and has a path switching function of the planar waveguide type. The input ports are connected to one ends of respective different sub-slab optical waveguides 12. The opposite side ends of the sub-slab optical waveguides 12 are optically coupled to one end of a common main slab optical waveguide 15 via arrayed optical waveguides 14. To the opposite side end of the main slab optical waveguide 15 are connected plural output ports 17. On the top of the arrayed optical waveguides 14, there are respectively arranged electrodes 13, each causing the difference in the refractive index of the respective optical waveguide.

Abstract: Arranged for at least one of a pair of branch optical waveguides in a Mach-Zehnder type interference optical system is a ring resonance type phase shifter for modulating a light wave signal propagating through the branch optical waveguide. The ring resonance type phase shifter includes a ring-type optical waveguide arranged so as to be mode-coupled with the corresponding branch optical waveguide, and is configured so that amplitude branching ratio K between the corresponding branch optical waveguide and the ring-type optical waveguide can be varied with a change in refractive index or the like, accompanied by voltage application to a pn junction, for example. As amplitude branching ratio K is varied, the phase difference between the light wave signals propagating through the paired optical waveguides varies, to thereby control the intensity of the light wave signal output from the interference optical system.

Abstract: An optical device including a substrate, a distributed feedback (DFB) semiconductor laser formed on the substrate and including a diffraction grating having an asymmetrical &lgr;/4 phase shift region, the diffraction grating extending along an optical axis of the DFB semiconductor laser, and a field absorbing modulator integrated with the DFB semiconductor laser on the substrate for modulating a light wave emitted from the DFB semiconductor laser, the optical modulator having a facet reflection rate between 0.01 and 0.02% at an output end thereof, the diffraction grating having a &kgr;L value between 1 and 1.2. The proper combinations of the &kgr;L value of the diffraction grating and the reflection rate of the output facet of the modulator of the DFB semiconductor laser can fabricate the source for integrating the modulator having the excellent quality with a higher yield and lower cost.

Abstract: A method for selecting a light source for optical communication system comprises the steps of: measuring time division chirping characteristics and optical response waveforms of the light source responding to a fixed strength random pulse signal; performing a simulation of a transmission process based on measured data; computing a selection parameter as an index for determining a dispersion tolerance quality of the light source according to a computed post-transmission waveform of an optical signal that propagated through an optical fiber path; and deciding the dispersion tolerance quality of the light source based on values of the selection parameter. There is no need for providing the usual facilities required for dispersion tolerance evaluation such as EDFA, optical fibers, wavelength filter, receiving disk and error rate detector and the like and the time required for selection is significantly reduced.

Abstract: Disclosed is an electroabsorption-type optical modulator, which has: a semiconductor substrate; and a semiconductor buffer layer, a semiconductor optical absorption layer and a semiconductor cladding layer which are layered in this order on the semiconductor substrate; wherein the absorption of a light wave supplied to an end of the semiconductor optical absorption layer is controlled by changing an intensity of electric field applied to the semiconductor optical absorption layer; and the semiconductor optical absorption layer has a region with absorption-edge wavelength shorter than that of the other region of the semiconductor optical absorption layer and a voltage corresponding an external electrical signal is simultaneously applied to both the regions of the semiconductor optical absorption layer, so that, to an incident light, a refractive index of the semiconductor optical absorption layer is decreased and an absorption coefficient of the semiconductor optical absorption layer is increased when an inten