A demodulation delay circuit is provided with an optical interferometer that comprises first arm-waveguides for connecting input-side couplers and output-side couplers, and second arm-waveguides shorter in optical path length than the first arm-waveguides, and that delays each of the bits of an input optical signal by approximately 1 bit so that the bits interfere with bits adjacent thereto. The light propagating direction of the optical interferometer is different, by 180 degrees, at the input-side couplers and at the output-side couplers. Each of the input-side couplers and the output-side couplers comprises first and second waveguides, the optical path length of the first waveguide is longer than that of the second waveguide, each of the first and second waveguides has a first directional coupler and a second directional coupler formed at two places in the longitudinal direction thereof, and the input-side couplers and the output-side couplers are configured as wavelength non-dependent couplers having a binding rate of approximately 50% in the wavelength band where the couplers are to be used. The side of the input-side couplers where the first waveguides are arranged with respect to the longitudinal direction of the input-side couplers and the side of the output-side couplers where the first waveguides are arranged with respect to the longitudinal direction of the output-side couplers are the same.
DEMODULATION DELAY CIRCUIT AND OPTICAL RECEIVER