| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a technique accurately reproducing data from an optical signal modulated using a differential M phase shift modulation system. <P>SOLUTION: A demodulator 1 has a heater 21 for applying phase shift to an optical signal obtained by branching an optical signal PS. A phase shift amount in the heater 212 is controlled by a control unit 50. The control unit 50 includes: a signal generator 52 for generating a low-frequency signal LFS1; an envelope detector 51 for detecting an envelope of an electric signal ES1; a manipulated variable determination section 53 for determining a control voltage VT1 for the heater 212 on the basis of a detection signal DS1 output from the envelope detector 51 and the low-frequency signal LFS1; and an adder 54 for outputting, as a control signal CS1, a signal obtained by adding the low-frequency signal LFS1 to the control voltage VT1. The heater 212 varies the phase shift amount in response to the control signal CS1. <P>COPYRIGHT: (C)2009,JPO&INPIT |
