| 摘要 |
PURPOSE:To decode a received signal into a signal having a correct side polarity by including an identification pulse signal in a transmission signal at the transmission side in an optical communication by the frequency shift keying extracting the identification pulse signal at the reception side so as to discriminate the inversion of the sign polarity. CONSTITUTION:Signals 7-10 of the 1st-4th series, for example, are inputted to a multiplex conversion circuit 4, where a transmission signal 11 subject to time division multiplex is obtained. In this case, an identification pulse signal 12 in common use with a frame synchronizing signal is inserted in the transmission signal 11 at each prescribed period. After the transmission signal 11 is amplified to a prescribed level by a drive circuit 5, the result is fed to an light source section 6, from which a signal light 13 subject to direct frequency shift keying by an applied current is outputted. The incident signal light 13 is synthesized with a local oscillation light 16 given from a local oscillation light source 15 by a synthesis circuit 14, subject to light heterodyne detection by a light at a photodetector 17 and converted into an intermediate frequency signal 18. A demodulation circuit 20 converts the intermediate frequency signal 18 into a demodulation output 22 of base band and a code identification circuit 23 detects the identification pulse signal 12. |
