| 摘要 |
PROBLEM TO BE SOLVED: To prevent elongation of a required time for adjusting a phase difference between a first optical signal to be phase-modulated and a second optical signal to be phase-modulated to a desired phase difference.SOLUTION: A bias setting circuit (10) selectively and repeatedly increases or decreases a bias voltage of an amount according to a variation amount detected by a variation amount detection circuit (24), so that a variation amount of power of synthetic optical signals detected by the variation amount detection circuit (24). Provided that the bias circuit (10) repeatedly increases the bias voltage while the power of the synthetic optical signal detected by a detector (16) is not less than predetermined power, instead of selectively and repeatedly increasing or decreasing the bias voltage of an amount according to the variation amount detected by the variation amount detection circuit (24). |
