Compact and Colorless PLC-Type 1-Bit Delay Line Interferometer for DQPSK Demodulator

A compact and colorless planar lightwave circuit (PLC) type 1-bit delay line interferometer for a differential quadrature phase-shift keying (DQPSK) demodulator is demonstrated by adopting wavelength insensitive couplers with narrow coupling waveguides and novel circuit arrangement suitable for integrated DQPSK receivers. The fabricated interferometer realizes a small chip size and practical properties in both entire C- and L-bands.