| 摘要 |
<p>Light having components of frequencies f<SUB>0</SUB>, f<SUB>+1</SUB> and f<SUB>-1</SUB> outputted from an optical modulator (10) is monitored, a second light detection means (14b) measures the power P2 of all the components, and a first light detection means (14a) measures the power P1 with frequency f<SUB>0</SUB> component cut out by a filter means (13). Based on these light receiving powers (P1) and (P2), phase differences imparted by the respective DC electrodes of Mach-Zehnder optical waveguides (MZ-A, MZ-B, MZ-C) of the optical modulator (10) are controlled. The control is performed to minimize the light receiving power (P1) and to maximize the light receiving power (P2).</p> |
