Patent ID: 7961991

Claim:
A delay demodulation device formed on a chip including a Planar Lightwave Circuit (PLC) for demodulating Differential Quadrature Phase Shift Keying (DQPSK) signals, comprising: an input waveguide, which receives the DQPSK signals, extending entirely in a one direction from a middle portion of an end face of the chip toward a center portion of the chip; a Y-shape waveguide, which splits the input waveguide into two waveguides; a first Mach-Zehnder interferometer comprising a first input coupler, which is connected to one of the two waveguides split by the Y-shape waveguide, a first output coupler, which is connected to first and second output waveguides, and two arm waveguides having different lengths with respect to each other and connected between the first input coupler and the first output coupler; a second Mach-Zehnder interferometer comprising a second input coupler, which is connected to an other of the two waveguides split by the Y-shape waveguide, a second output coupler, which is connected to third and forth output waveguides, and two arm waveguides having different lengths with respect to each other and connected between the second input coupler and the second output coupler; a first delay portion formed in the first and second output waveguides to match the lengths of the first and second output waveguides; and a second delay portion formed in the third and fourth output waveguides to match the lengths of the third and forth output waveguides, wherein ends of both the arm waveguides of the first Mach-Zehnder interferometer and ends of both the arm waveguides of the second Mach-Zehnder interferometer are bent toward a center portion of the PLC, and the two waveguides split by the Y-shape waveguide, the first and second Mach-Zehnder interferometers, the output waveguides of the first Mach-Zehnder interferometer and the output waveguides of the second Mach-Zehnder interferometer, and the first and second delay portions are respectively formed at symmetrical positions on the chip with respect to a virtual centerline of the chip extending from the input waveguide in the one direction.