To execute communication by means of simple circuit configuration by detecting plural change points of the symbols of a transmission digital signal, detecting the values of the symbols between the detecting change point to the next, converting them into previously decided digital codes, converting them into high-speed digital signals by every symbol of the signal to be transmitted and multiplexing them.
The change in the respective symbol values of the inputted digital signal S2 is detected by a signal change detecting circuit 4, and the values of the respective symbols are detected and decided by a signal level deciding circuit 5. They are converted into the high speed digital signals by binary digital codes corresponding to the quaternary symbols by an encoding circuit 6, the signals corresponding to the symbols are multiplexed by selective exchange by a code selecting circuit 7, and then, they are outputted to a transmission line from an optical transmitting circuit 8 as a transmission optical signal. The received optical signals are decoded by a decoding circuit 10, the error of the codes is checked by a code error detecting circuit 11, and conversion to the binary digital encoded signals is executed precisely.
IMAMURA NOBUO
UCHINO FUMITAKA
