OPTICAL PHASE MODULATION DEMODULATION CIRCUIT AND OPTICAL PHASE MODULATION DEMODULATION METHOD

摘要

PROBLEM TO BE SOLVED: To simplify the adjustment of a center frequency of a delay Mach-Zehnder interferometer used for optical phase modulation adopting the DQPSK system.;SOLUTION: An optical phase modulation circuit is provided with: a CW light source; a phase modulator for applying periodic phase modulation with a phase shift of 0 to π/4 to a received optical signal by using a clock whose frequency is a half the symbol rate; and an optical orthogonal phase modulator that distributes the received optical signals into two paths, applies phase modulation of 0 to π to the respective optical signals, and again synthesizes them by deviating the phase of the one optical signal by π/2, wherein the components above are connected in series in the order of the CW light source, the phase modulator, and the optical orthogonal phase modulator, or in the order of the CW light source, the optical orthogonal phase modulator, and the phase modulator.;COPYRIGHT: (C)2008,JPO&INPIT