| 摘要 |
<P>PROBLEM TO BE SOLVED: To control a phase difference between both arms of an optical interferometer to an optimum value, in an optical receiving apparatus for receiving an optical differential quaternary phase shift keying (DQPSK) signal. <P>SOLUTION: An optical DQPSK signal is made incident on two optical interferometers in each which a delay-time difference between two arms is set to be equal to a 1-symbol time of the optical DQPSK signal and which are orthogonal to each other. The optical receiving apparatus 100 converts the optical DQPSK signal into an intensity signal and receives it. A differential amplifier 11, 12 obtains a difference signal between outputs of a pre-amplifier 15, 16 and a discriminator 17, 18 connected thereto. The difference signal includes, as an amplitude, a phase shift in a phase section 22, 23. A control circuit 40, 50 adjusts the phase of the phase section 22, 32 in the optical interferometers 20, 30 to reduce this difference signal, so that the phase difference between the two arms is set to a desired phase difference. <P>COPYRIGHT: (C)2010,JPO&INPIT |
