| 摘要 |
PROBLEM TO BE SOLVED: To prevent damage in an electric absorption type optical modulator by controlling so as not to apply a forward voltage to the electric absorption type optical modulator even in an instance such as that an applied voltage to the electric absorption type optical modulator is kept to a prescribed value or above, etc., when a power source of a drive circuit is raised and lowered. SOLUTION: When the power source of the drive circuit 1 is raised, a charge circuit 7 is charged by a DC bias voltage source 2, and the charged voltage is applied from a bias tee 4 to the electric absorption type optical modulator 5. When the charged voltage becomes a threshold value or above, a switch 10a is closed after a prescribed delay by a voltage detector 9, and an AC modulation voltage source 3 is connected to the bias tee 4, and the DC bias voltage and the AC modulation voltage are applied to the optical modulator 5 together with each other. On the other hand, when the power source of the drive circuit 1 is lowered, though the switch 10a is turned off by a control circuit 8a, and the AC modulation voltage is interrupted, the DC bias voltage is lowered gradually while discharging the voltage charged in the charge circuit 7 to the optical modulator 5. |
