Patent ID: 8320779

Claim:
A receiver for use in a system for transmitting a WDM light produced by multiplexing a plurality of DPSK-modulated light signals, comprising: a wavelength demultiplexer for demultiplexing said WDM light into light signals at respective central frequencies thereof; a delay interferometer for converting a light signal output from said wavelength demultiplexer into an intensity signal; a light detector for converting said intensity signal into an electric signal; and a logic inverting circuit for outputting the output signal from said light detector while non-inverting or inverting the logic level thereof depending on the frequency of a light signal output from said wavelength demultiplexer; wherein the interval between interferential frequencies at which the output signal output from said delay interferometer is maximum is 2/(2n+1) times the interval between the central frequencies of said WDM light, where n represents a positive number.