Abstract: A planar lightwave circuit is provided. The planar lightwave circuit includes a waveguide and a spotsize converter which is a part of the waveguide, wherein a core is embedded in a cladding in the waveguide, and the spotsize converter is located near an end face of a substrate on which the planar lightwave circuit is formed, the spotsize converter including: a core width fine-tuning part in an end face side of the substrate; and a core width converting part which follows the core width fine-tuning part; wherein core width of the spotsize converter is minimum at an end face of the substrate, a mean taper angle ?1 of the core width fine-tuning part is larger than 0° and smaller than a mean taper angle ?2 of the core width converting part.

Abstract: A low-cost, high-reliability polarization-independent optical waveguide interferometer is proposed which does not bring about any additional job involved in the insertion of a half-wave plate or excess loss of light. In an optical multi/demultiplexer utilizing optical interference of light waves passing through a plurality of optical waveguides with different lengths, such as an AWG and a Mach-Zehnder interferometer, longitudinal integral values of birefringence values of the individual waveguides, which values are variable or invariable along the waveguides, are made equal for all waveguides 201 and 202. Thus, simply varying the waveguide width can implement polarization-independent operation, or on the contrary implement a polarization beam splitter.

Abstract: The present invention provides an optical demultiplexer and an optical multiplexer the transmission characteristics of which are unlikely to be affected by fabrication errors and which have small group delay dispersion. A cross output port (X-OUT) of a second optical demultiplexer element (DEMUX) is selected, and a through output port (T-OUT) of a third DEMUX is selected. A T-OUT of a first DEMUX has a passband equal to the X-OUT of the second DEMUX, and a X-OUT of the first DEMUX has a passband equal to the T-OUT of the third DEMUX. The T-OUT of the first DEMUX has group delay characteristics opposite to those of the X-OUT of the second DEMUX, and the X-OUT of the first DEMUX has group delay characteristics opposite to those of the T-OUT of the third DEMUX.

Abstract: It is an object of the present invention to reduce the size of a circuit and the adverse effects of fabrication errors, while increasing yield. Signal light incident on a circuit through input waveguides propagates from the exterior to interior of the circuit while rotating counterclockwise. The signal light passes through a point of inflection in the center of the circuit, subsequently propagate clockwise from the interior to exterior of the circuit, and then exit output waveguides. Two arms constituting a delay circuit and optical couplers can be integrated together at such an interval that they are not coupled together. Therefore, the size of the circuit can be reduced compared to the prior art.

Abstract: An optical multi/demultiplexer is provided that has a wide passband and small crosstalk among its all channels. It includes first and second arrayed waveguide gratings and a 2×2 optical signal processor. The 2×2 optical signal processor includes first to fourth directional couplers, and first to third delay lines. The first to third delay lines have thin film heater phase shifters for correcting phase errors involved in fabrication. Utilizing the 2×2 optical signal processor having a transmission spectrum with a square profile having a wide passband and rejection band makes it possible for the optical multi/demultiplexer that combines the arrayed waveguide gratings with the waveguide type circulating filter (2×2 optical signal processor) to widen the extinction bandwidth of the adjacent channel.

Abstract: A no polarization dependent waveguide type optical circuit can resolve polarization dependency completely and can reduce reflected return light. An intermediate portion of the two connecting waveguides are formed with S-shaped waveguides of the same shape consisted of respectively two curved waveguides or two curved waveguides and straight waveguides connecting the curved waveguides. One polarization mode converter is provided in a groove formed across the S-shaped waveguide, and a perpendicular line to an incident surface of light of the polarization mode converter and the S-shaped waveguide forms an angle greater than 0°.

Abstract: It is an object of the present invention to reduce the size of a circuit and the adverse effects of fabrication errors, while increasing yield. Signal light incident on a circuit through input waveguides propagates from the exterior to interior of the circuit while rotating counterclockwise. The signal light passes through a point of inflection in the center of the circuit, subsequently propagate clockwise from the interior to exterior of the circuit, and then exit output waveguides. Two arms constituting a delay circuit and optical couplers can be integrated together at such an interval that they are not coupled together. Therefore, the size of the circuit can be reduced compared to the prior art.

Abstract: A low-cost, high-reliability polarization-independent optical waveguide interferometer is proposed which does not bring about any additional job involved in the insertion of a half-wave plate or excess loss of light. In an optical multi/demultiplexer utilizing optical interference of light waves passing through a plurality of optical waveguides with different lengths, such as an AWG and a Mach-Zehnder interferometer, longitudinal integral values of birefringence values of the individual waveguides, which values are variable or invariable along the waveguides, are made equal for all waveguides 201 and 202. Thus, simply varying the waveguide width can implement polarization-independent operation, or on the contrary implement a polarization beam splitter.

Abstract: A planar lightwave circuit is provided. The planar lightwave circuit includes a waveguide and a spotsize converter which is a part of the waveguide, wherein a core is embedded in a cladding in the waveguide, and the spotsize converter is located near an end face of a substrate on which the planar lightwave circuit is formed, the spotsize converter including: a core width fine-tuning part in an end face side of the substrate; and a core width converting part which follows the core width fine-tuning part; wherein core width of the spotsize converter is minimum at an end face of the substrate, a mean taper angle &thgr;1 of the core width fine-tuning part is larger than 0° and smaller than a mean taper angle &thgr;2 of the core width converting part.

Abstract: The present invention provides an optical demultiplexer and an optical multiplexer the transmission characteristics of which are unlikely to be affected by fabrication errors and which have small group delay dispersion. A cross output port (X-OUT) of a second optical demultiplexer element (DEMUX) is selected, and a through output port (T-OUT) of a third DEMUX is selected. A T-OUT of a first DEMUX has a passband equal to the X-OUT of the second DEMUX, and a X-OUT of the first DEMUX has a passband equal to the T-OUT of the third DEMUX. The T-OUT of the first DEMUX has group delay characteristics opposite to those of the X-OUT of the second DEMUX, and the X-OUT of the first DEMUX has group delay characteristics opposite to those of the T-OUT of the third DEMUX.

Abstract: An optical multi/demultiplexer is provided that has a wide passband and small crosstalk among its all channels. It includes first and second arrayed waveguide gratings and a 2×2 optical signal processor. The 2×2 optical signal processor includes first to fourth directional couplers, and first to third delay lines. The first to third delay lines have thin film heater phase shifters for correcting phase errors involved in fabrication. Utilizing the 2×2 optical signal processor having a transmission spectrum with a square profile having a wide passband and rejection band makes it possible for the optical multi/demultiplexer that combines the arrayed waveguide gratings with the waveguide type circulating filter (2×2 optical signal processor) to widen the extinction bandwidth of the adjacent channel.

Abstract: A no polarization dependent waveguide type optical circuit can resolve polarization dependency completely and can reduce reflected return light. An intermediate portion of the two connecting waveguide are formed with S-shaped waveguides of the same shape consisted of respectively two curved waveguides or two curved waveguides and straight waveguides connecting the curved waveguides. One polarization mode converter is provided in a groove formed across the S-shaped waveguide, and a perpendicular line to an incident surface of light of the polarization mode converter and the S-shaped waveguide forms an angle greater than 0°.

Abstract: The present invention provides a wavelength division multiplexing filter that requires lower costs, a smaller size, and a smaller amount of fiber routing operations. According to the present invention, a first module constitutes a first filter. A second module constituting a second filter is produced by connecting together circuits identical in number to a plurality of output ports of the first module, the circuits each comprising a combination of directional couplers and Bragg gratings both formed of silica-based-glass waveguides, the circuits each having a wavelength selection characteristic so as to correspond to each of the output ports. The second module is connected to the first module via an 8-fiber ribbon to simplify the integration and connection of the circuits.