| 摘要 |
PURPOSE:To high sensitively receive tracking signals without causing the degradation of the main signals. CONSTITUTION:A transmitting circuit 10 switches the output of the two kinds of multilevel PPM modulation circuits 1 and 2 to PPM convert a main signal Sm simultaneously by a switch 4 corresponding to the logical level of a tracking signal Ss. A multilevel PPM signal Sp of the result of the switching is E/0 converted by an E/O 5 and becomes an optical signal St. At a receiving circuit 20, a received tracking signal Ssr is reproduced from a received signal Sr from an 0/E 18 by a low-pass filter 17. Quaternary and binary PPM demodulation circuits 12 and 13 demodulate the received signal Sr which is PPM converted from a delay circuit 11 simultaneously at a timing which a timing reproducing circuit 14 generates. A switch control circuit 16 controls a switch 13 based on the level of the received tracking signal Ssr, thus, received main signal Smr is obtained from either one of the PPM demodulation circuit 12 and 13. |
