| 摘要 |
PROBLEM TO BE SOLVED: To prevent a sensitivity from being lowered by connecting modulation electrodes of at least two optical modulators among optical modulators in series each other so that the same electric signals are impressed on them with the same phases to use single mode optical fibers without depending on the polarized plane of the outgoing light of a light siurce. SOLUTION: The AC voltage induced in a receiving antenna 33 passes through an impedance mudulating circuit 35 to be impressed on two optical modulators 41, 42 connected in series. The modulation electrodes of the two modulators 41, 42 are connected in series so that the same electric signals are impressed on them with the same phases. In this case, since coaxial cables of 50Ωs are used in this device, the impedance of a closed circuit consisting of the modulation electrodes and the impedance modulating circuit becomes double and the voltage drip to be impressed on the modulation electrodes becomes half and the sensitivity is enhanced. Then, the light made incident on respective optical modulators 41, 42 is modulated by impression voltages impressed on the modulation electrodes and is emitted to be made incident on a photodetector 32.
|
