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: A Mach-Zehnder interferometer circuit (700) is provided with two couplers (722, 724) and two arm waveguides (706, 708) connecting the couplers with each other, each fabricated on a substrate, in which a polarization rotation device (732) is disposed in a groove dividing each of the two arm waveguides into two, the polarization rotation device (732) for converting vertically polarized light into horizontally polarized light, and birefringence is adjusted by performing laser irradiation or the like partially into at least one of the two arm waveguides such that a difference between birefringence values divided by an optical wavelength to be used is within a range of 2m?0.2 to 2m+0.2 (m is an integer including zero), the birefringence values being those integrated linearly along the respective two arm waveguides in an optical signal travelling direction.

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: The present invention discloses an interferometer optical switch that can carry out switching over a broad band and has a high extinction ratio and large fabrication tolerance. The interferometer optical switch employs a phase generating coupler, the phase difference of the output of which has wavelength dependence, as at least one of the optical multi/demultiplexing device included in the interferometer optical switch. A wavelength insensitive interferometer optical switch is implemented by making the sum 2?{?1(?)+??L(?)+?2(?)} constant regardless of the wavelength, where ?1(?) is the phase produced by the first optical multi/demultiplexing device, 2???L(?) is the phase difference of the optical delay line with an optical path length difference of ?L, and 2??2(?) is the phase produced by the second optical multi/demultiplexing device.

Abstract: An optical multi/demultiplexing circuit includes at least one phase generating optical coupler and an optical delay line coupled to the phase generating optical coupler. The phase generating optical coupler consists of at least one input and at least two outputs. At least one of the phase generating optical coupler has a wavelength dependent or frequency dependent output phase difference in the passband of the circuit so that it can change the transmittance characteristics of the optical multi/demultiplexing circuit.

Abstract: The present invention discloses an interferometer optical switch that can carry out switching over a broad band and has a high extinction ratio and large fabrication tolerance. The interferometer optical switch employs a phase generating coupler, the phase difference of the output of which has wavelength dependence, as at least one of the optical multi/demultiplexing device included in the interferometer optical switch. A wavelength insensitive interferometer optical switch is implemented by making the sum 2?{?1(?)+??L(?)+?2(?)} constant regardless of the wavelength, where ?1(?) is the phase produced by the first optical multi/demultiplexing device, 2???L(?) is the phase difference of the optical delay line with an optical path length difference of ?L, and 2??2(?) is the phase produced by the second optical multi/demultiplexing device.

Abstract: An optical multi/demultiplexing circuit includes at least one phase generating optical coupler and an optical delay line coupled to the phase generating optical coupler. The phase generating optical coupler consists of at least one input and at least two outputs. At least one of the phase generating optical coupler has a wavelength dependent or frequency dependent output phase difference in the passband of the circuit so that it can change the transmittance characteristics of the optical multi/demultiplexing circuit.

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: It is an object of the present invention to provide an optical filter which allows parameters to be easily adjusted, which allows birefringence and temperature dependence to be easily compensated for, and which is essentially free from dispersion. The optical filter includes an optical coupler that splits light into two beams, optical couplers connected to outputs of the optical coupler, a first group of two optical waveguide delay lines connected to the coupler, a second group of two optical waveguide delay lines connected to the coupler, an optical coupler that combines lights from the first group of the lines, an optical coupler that combines lights from the second group of the lines, and a multimode interference optical coupler that combines lights from the couplers together.

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: It is an object of the present invention to provide an optical filter which allows parameters to be easily adjusted, which allows birefringence and temperature dependence to be easily compensated for, and which is essentially free from dispersion. The optical filter includes an optical coupler that splits light into two beams, optical couplers connected to outputs of the optical coupler, a first group of two optical waveguide delay lines connected to the coupler, a second group of two optical waveguide delay lines connected to the coupler, an optical coupler that combines lights from the first group of the lines, an optical coupler that combines lights from the second group of the lines, and a multimode interference optical coupler that combines lights from the couplers together.

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: 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.