| 摘要 |
<P>PROBLEM TO BE SOLVED: To obtain a QPSK modulator that maintains a phase difference between the I phase and the Q phase to π/2. <P>SOLUTION: The QPSK modulator includes: a means for splitting incident light into two beams; a first phase modulating means for modulating the phase of one of the branched beams; a second phase modulating means for modulating the phase of the other branched beam; a phase shifting means disposed in a preceding stage or a succeeding stage of the first or second phase modulating means; a means for coupling the beams that have respectively passed through the first phase modulating means and the second modulating means, and outputting the coupled beams as an optical signal; a means for converting a part of the outputted optical signal into an electric signal; a means for detecting a peak value of the amplitude of the optical signal from the electric signal and outputting a peak detection signal; a means for generating a dither signal; a phase comparing means for comparing phases of the peak detection signal and of the dither signal and generating a deviation signal in accordance with the deviation from the phase shift amount π/2 in the phase shifting means; and a feedback control means for superposing the dither signal on the deviation signal and feedback-controlling the phase shifting means to adjust the phase shift amount to π/2. <P>COPYRIGHT: (C)2011,JPO&INPIT |
