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 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 electrically controlled optical device effective index includes a traveling wave electrode, a shield conductor and a thick buffer layer of a low dielectric constant. The thickness of an overlaid layer disposed between the traveling wave electrode and the shield conductor as well as the thickness of the buffer layer is so determined that an effective index of a microwave transmitted through the traveling wave electrode approaches an effective index of light transmitted through an optical waveguide, and that a microwave conductor loss is reduced, and that a characteristic impedance of said traveling wave electrode approaches a characteristic impedance of an associated external microwave circuit.

Abstract: An electrically controlled optical device includes a traveling wave electrode structure, a shield conductor and a thick buffer layer having a low dielectric constant. The thickness of an overlaid layer disposed between the traveling wave electrode structure and the shield conductor, as well as the thickness of the buffer layer, is determined so that the effective index of a microwave transmitted through the traveling wave electrode structure approaches the effective index of light transmitted through an optical waveguide, so that the microwave conductor loss is reduced, and so that the characteristic impedance of the traveling wave electrode structure approaches the characteristic impedance of an associated external microwave circuit.