| 摘要 |
Beams having components of frequencies f0, f+1, and f-1 output from an optical modulation unit (10) are monitored, a second optical detector (14b) measures a beam reception power P2 of the beam having the components of entire frequencies, and a first optical detector (14a) measures a beam reception power P1 of the bearn having the component of frequency fo filtered by a filter unit (13), so that a phase difference applied by respective DC electrodes of Mach-Zehnder optical waveguides MZ-A, MZ-B, and MZ-C of the optical modulation unit (10) on the basis of the beam reception powers P1 and P2 is controlled. The controlling is performed so that the beam reception power P1 is a minimum value and the beam reception power P2 is a maximum value.
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