| 摘要 |
The purpose of the present invention is to correct and make uniform the amount of phase modulation in various phase modulation regions of an optical modulator during operation. An optical modulating unit (11) outputs an optical signal with a four level modulation. A signal distribution circuit (12) outputs signals (D0 - D2, Dcal) on the basis of an input digital signal (DIN). A drive circuit (14) outputs drive signals from drivers (DR10 - DR12) and the calibration driver (DR100) connected with phase modulation regions (PM1_0 - PM1_2, PM2_0 - PM2_2) and calibration phase modulation regions (PM10, PM20). A control circuit (13) calibrates the amplitude of the drive signals output by the drivers (DR10 - DR12) so as to correspond to the amount of phase modulation for calibration phase modulation regions (PM10, PM20) according to the optical intensity of the optical signal. |
