Optical differential quadrature phase shift keying(DQPSK) signal demodulation is one of the key technologies to accomplish a phase-modulated optical fiber communication system.In this paper,we design and setup a 2-bit delay interferometer(DI) utilizing YVO4 crystals,which is used as a DQPSK signal demodulator.Compared with the traditional DI usually based on fibers,the crystal based DI gains an advantage of higher temperature stability,which therefore will have a broad prospect in application as a key devic...