| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To control, with a simple configuration, a bias of an optical modulator having a nested waveguide to be used for DQPSK (Differential Quadrature Phase Shift Keying) modulation. <P>SOLUTION: The optical modulator has a nested waveguide configured by mounting two sub-Mach-Zehnder waveguides SMZ1 and SMZ2 on two branched waveguides, respectively, in one main Mach-Zehnder waveguide MMZ. The optical modulator further includes modulation parts ME1 to ME3. The method includes: while applying low-frequency signals having the same frequency (f) and 90 degree different phase to the modulation part provided on each of the sub-Mach-Zehnder waveguides, detecting a portion of lightwave output from the corresponding sub-Mach-Zehnder waveguide in each of the sub-Mach-Zehnder waveguides, and performing bias control BC1 and BC2 of the modulation parts in the sub-Mach-Zehnder waveguide based on detection values; and detecting a portion of the lightwave output from the main Mach-Zehnder waveguide, and performing bias control BC3 of the modulation parts in the main Mach-Zehnder waveguide based on the detection values. <P>COPYRIGHT: (C)2011,JPO&INPIT</p> |
