Abstract: A low-loss optical switch device with a smaller number of ports for an optical switch in a network and node device capable of transmitting OCS-type and OPS-type optical signals is provided. The optical switch device includes: a high-speed add/drop optical switch composed of a plurality of optical switches, the optical switch having an optical waveguide structure made of a material whose refractive index or absorption coefficient changes on the order of nanoseconds, and the optical switch changing the refractive index or the absorption coefficient to perform switching of both OCS optical signals, which are optical-circuit-switching-type optical signals, and OPS optical signals, which are optical-packet-switching-type optical signals; and a plurality of circulators connected to an input port and an output port of the high-speed add/drop optical switch.

Abstract: An optical 90-degree hybrid circuit includes: first and second optical splitters for receiving and splitting a first and second light beam into two, respectively; a first optical coupler for generating an interfering light beam by multiplexing one of the light beams split by the first optical splitter and the second optical splitter; and a second optical coupler for generating an interfering light beam by multiplexing another one of the light beams split by the first optical splitter and the second optical splitter. The first optical splitter includes an optical coupler configured to output two light beams having equal phases, and the second optical splitter includes an optical coupler configured to output two light beams having a phase difference of 90 degrees.

Abstract: An optical wavelength multi/demultiplexer having transmission characteristics with a higher rectangular degree than a conventional one includes an AWG and two-stage lattice circuit. An example of a two-stage lattice circuit according to the present invention includes an input waveguide, a third optical coupler, a third and fourth arm waveguides, a second optical coupler, a first and second arm waveguides, a first optical coupler, and output waveguides. The optical path length differences between the third and fourth arm waveguides and between the first and second arm waveguides are designed to be ?L. The path passing the third and first arm waveguides differs by 2·?L in optical length from that the fourth and second arm waveguides. The paths passing the third and second arm waveguides and passing the fourth and first arm waveguides differ by ?L from that passing the fourth and second arm waveguides.

Abstract: The present invention provides an optical 90-degree hybrid circuit for reducing wavelength dependency of an IQ phase difference. An optical 90-degree hybrid circuit according to the present invention comprises a first demultiplexing optical coupler including a first and second input port, a second demultiplexing optical coupler including a third and fourth input port, first and second arm waveguides connected to the first and second input port, each having the same length, a third and fourth arm waveguides connected to the third and fourth input port, each having the same length, a 90-degree phase shift section installed in one of the first to fourth arm waveguides, a first optical coupler connected to the first and third arm waveguide, and a second optical coupler connected to the second and fourth arm waveguide, the light is inputted into the first and fourth input port or into the second and third input port.

Abstract: An optical 90-degree hybrid circuit includes a first demultiplexing optical coupler having two or more first input ports and two or more first output ports, a second demultiplexing optical coupler having two or more second input ports and two or more second output ports, two first arm waveguides connected to the first output ports, two second arm waveguides connected to the second output ports, a 90-degree phase shift section installed in one of the four arm waveguides, a first optical coupler and a second optical coupler connected to the first arm waveguides and the second arm waveguides, a first optical waveguide for connecting an optical splitter and the first input ports, and a second optical waveguide for connecting the optical splitter and the second input ports, wherein an optical length of the first optical waveguide is different from that of the second optical waveguide.

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Abstract: When a conventional synchronized AWG is employed to extend a transmission passband, an increase in loss near the optical center frequency can not be avoided. Because of passband width limit, a problem has existed in that the synchronized AWG could not be applied for a large, complicated communication system wherein a signal light passes a number of points. Therefore, an optical wavelength multiplexing/demultiplexing circuit of the present invention is a synchronized AWG, which includes an optical splitter arranged in an interference circuit that is connected on the side of one slab waveguide. The splitting ratio of the optical splitter varies, depending on the optical frequency, and the value becomes minimum near the optical center frequency of the synchronized AWG. The optical splitter is operated so that the splitting ratio is comparatively great at optical frequencies distant from the optical center frequency.

Abstract: An optical modulator having a high stability is provided. In the optical modulator according to the present invention, a phase modulation by an electro-optic effect is made on an optical substrate of an electro-optic material while the setting of an operating point by a thermal-optic effect is made on a planar lightwave circuit (PLC) substrate of quartz, silicon, or the like. Such configuration can suppress the influence of thermal drift or the like because no heat is applied directly to the optical substrate of the electro-optic material. In addition, breakage and warpage of the substrate due to heat are also mitigated. Further, quartz used for the PLC has a low thermal conductivity, approximately one-fifth of that of the LN substrate (approximately 1 W/(m·K)), and therefore, a desired phase difference can be maintained with a low power consumption, and thus, the operating point becomes stabilized.

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Abstract: An optical wavelength multi/demultiplexer having transmission characteristics with a higher rectangular degree than a conventional one includes an AWG and two-stage lattice circuit. An example of a two-stage lattice circuit according to the present invention includes an input waveguide, a third optical coupler, a third and fourth arm waveguides, a second optical coupler, a first and second arm waveguides, a first optical coupler, and output waveguides. The optical path length differences between the third and fourth arm waveguides and between the first and second arm waveguides are designed to be ?L. The path passing the third and first arm waveguides differs by 2·?L in optical length from that the fourth and second arm waveguides. The paths passing the third and second arm waveguides and passing the fourth and first arm waveguides differ by ?L from that passing the fourth and second arm waveguides.

Abstract: The present invention provides an optical 90-degree hybrid circuit for reducing wavelength dependency of an IQ phase difference. An optical 90-degree hybrid circuit according to the present invention comprises a first demultiplexing optical coupler including a first and second input port, a second demultiplexing optical coupler including a third and fourth input port, first and second arm waveguides connected to the first and second input port, each having the same length, a third and fourth arm waveguides connected to the third and fourth input port, each having the same length, a 90-degree phase shift section installed in one of the first to fourth arm waveguides, a first optical coupler connected to the first and third arm waveguide, and a second optical coupler connected to the second and fourth arm waveguide, the light is inputted into the first and fourth input port or into the second and third input port.

Abstract: An optical 90-degree hybrid circuit includes a first demultiplexing optical coupler having two or more first input ports and two or more first output ports, a second demultiplexing optical coupler having two or more second input ports and two or more second output ports, two first arm waveguides connected to the first output ports, two second arm waveguides connected to the second output ports, a 90-degree phase shift section installed in one of the four arm waveguides, a first optical coupler and a second optical coupler connected to the first arm waveguides and the second arm waveguides, a first optical waveguide for connecting an optical splitter and the first input ports, and a second optical waveguide for connecting the optical splitter and the second input ports, wherein an optical length of the first optical waveguide is different from that of the second optical waveguide.

Abstract: An optical 90-degree hybrid circuit includes: first and second optical splitters for receiving and splitting a first and second light beam into two, respectively; a first optical coupler for generating an interfering light beam by multiplexing one of the light beams split by the first optical splitter and the second optical splitter; and a second optical coupler for generating an interfering light beam by multiplexing another one of the light beams split by the first optical splitter and the second optical splitter. The first optical splitter includes an optical coupler configured to output two light beams having equal phases, and the second optical splitter includes an optical coupler configured to output two light beams having a phase difference of 90 degrees.

Abstract: In an optical interferometer, polarization dependence attributable to the optical path difference has conventionally been eliminated by inserting a half-wave plate at the center of the interferometer. However, light induced by polarization coupling produced in directional couplers used in the optical interferometer causes interference having different interference conditions from those of the normal light. Polarization rotators that effect any one of 90° rotation and ?90° rotation of all states of polarization of incoming light are inserted in the optical interferometer, and thereby the interference conditions of light induced by polarization coupling are made the same as those of the normal light. Each of the polarization rotators is implemented by using two half-wave plates and by varying an angle of combination of these half-wave plates. Alternatively, each of the polarization rotators is implemented through a combination of one half-wave plate and a waveguide having birefringence properties.

Abstract: When a conventional synchronized AWG is employed to extend a transmission passband, an increase in loss near the optical center frequency can not be avoided. Because of passband width limit, a problem has existed in that the synchronized AWG could not be applied for a large, complicated communication system wherein a signal light passes a number of points. Therefore, an optical wavelength multiplexing/demultiplexing circuit of the present invention is a synchronized AWG, which includes an optical splitter arranged in an interference circuit that is connected on the side of one slab waveguide. The splitting ratio of the optical splitter varies, depending on the optical frequency, and the value becomes minimum near the optical center frequency of the synchronized AWG. The optical splitter is operated so that the splitting ratio is comparatively great at optical frequencies distant from the optical center frequency.

Abstract: An optical modulator having a high stability is provided. In the optical modulator according to the present invention, a phase modulation by an electro-optic effect is made on an optical substrate of an electro-optic material while the setting of an operating point by a thermal-optic effect is made on a planar lightwave circuit (PLC) substrate of quartz, silicon, or the like. Such configuration can suppress the influence of thermal drift or the like because no heat is applied directly to the optical substrate of the electro-optic material. In addition, breakage and warpage of the substrate due to heat are also mitigated. Further, quartz used for the PLC has a low thermal conductivity, approximately one-fifth of that of the LN substrate (approximately 1 W/(m·K)), and therefore, a desired phase difference can be maintained with a low power consumption, and thus, the operating point becomes stabilized.

Abstract: A demodulator is provided for a multilevel differential phase shift keyed signal, capable of eliminating polarization dependence due to birefringence and polarization coupling-induced light resulting from a waveguide structure, and also, polarization dependence due to dynamic birefringence produced at the time of driving a variable phase adjuster. The demodulator is configured of an optical delay line interferometer of a waveguide interference type. The S/N ratio of a demodulated signal in the demodulator formed by the optical delay line interferometer can be also improved. Further, both the polarization dependence and the temperature dependence of the optical delay line interferometer can be reduced. The disposition of a polarization converter and groves filled with a temperature compensation material makes it possible to provide a circuit configuration suitable for eliminating the polarization dependence and the temperature dependence of the optical delay line interferometer.