| 摘要 |
PURPOSE:To prevent deterioration in the S/N of a reception signal by dividing a band characteristic of a band pass filter into two in matching with plural received waves, selecting freely the carrier frequency and narrowering the pass band of the band pass filter. CONSTITUTION:Two kinds of frequencies f0, f1 are assigned as signals corresponding to data 1, 0. The optical modulated by the frequencies f0 and f1 is received by a photodetector 21 and amplified by an amplifier 22. After the output of the amplifier 22 is branched into two by a branching device 24, the result is inputted respectively to band pass filters 25, 26. The characteristic of one band pass filter 25 has a narrow pass band W0 including the frequency f0 and the characteristic of the other band pass filter 26 has a narrow pass band W1 including the frequency f1. Thus, only the carrier signal f0 is outputted to an output of the band pass filter 25 and only the carrier signal f1 is outputted to the output of the band pass filter 26. After the outputs of the two filters 25, 26 are synthesized by a synthesizer 27, the result is amplified by an amplifier 23 and demodulated by a demodulator 28. |
