| 摘要 |
PROBLEM TO BE SOLVED: To improve the receiving sensitivity and to increase the communication distance for a multivalued optical signal whose power level increases in sequence from a 1st step to the N-th step by setting the power level of each step in such a way where the power level monotonously increases. SOLUTION: An optical modulator 12 of an optical transmitter 1 modulates the laser beam sent from a laser light source 11 by the ternary electric signal received from a ternary encoder 2 and sends the modulated laser beam to an optical transmission line 3 as an optical signal. The optical amplifiers 31-1, 31-2 and 31-n are inserted to the line 3 at every fixed distance and compensate the attenuation of the optical signal. Then a photoelectric converter 41 of an optical receiver 4 converts the optical signal into an electric signal, and the 1st and 2nd identifiers 43 and 44 identify the electric signal to send it to a ternary decoder 5 as a ternary digital electric signal. A nonlinear circuit 15 distorts and outputs a waveform by mean of the nonlinearity of a diode, so that the ratio of a high level difference of the ternary electric signal is set at 2 to 3 against a low level difference. |
