| 摘要 |
PROBLEM TO BE SOLVED: To enable transmission with a high S/N without degrading characteristics by transmitting an optical signal while modulating its polarization through a control signal. SOLUTION: According to an information signal, the optical signal from a light source LD 1 is modulated by an optical modulator 4 and according to an output control signal 51 of a control signal generating circuit 6, the polarizing plane of the optical signal is modulated. Further, the polarizing plane of the optical signal is modulated by a control signal 52 of long synchronism with the control signal 51 by a polarized light modulator 9. This demodulation is performed for making the polarization on a transmission line with the polarizing plane of a polarizer for control signal extraction on the side of reception since the polarization is changed slowly in comparison with the control signal 51. On the side of reception, received light is amplified and branched, and the optical signal polarized and modulated by the control signal is extracted by the polarizer and converted to an electric signal. Thus, since the intensity of the optical signal does not fluctuate, without degrading the characteristics of the information signal, the control signal of high output can be provided through a simple circuit to which only the polarizer is added. |
