To improve the reception sensitivity of an up signal.
A DFB laser 16 of a control station 10 outputs CW laser beam with wavelength λu. The laser beam is incident on an optical modulator 48 through an optical circulator 18 and an optical fiber 32. A deplexer 46 supplies an up signal Su from an antenna 42 to the optical modulator 48. A surface 48a of the optical modulator 48 which faces optical fiber 32 is a partially reflecting surface for the wavelength λu and the opposite surface 48b is a 100% reflecting surface for the wavelength λu. The light (unmodulated light) which is reflected on a front end surface 48a of the optical modulator 48 and the light (modulated light) which is totally reflected on an end surface 48b of the optical modulator and has its intensity modulated with the up signal Su while traveling forward and backward in the optical modulator 48 are both outputted to an optoelectric transducer 20 through the optical fiber 32 and optical circulator 18. The optoelectric transducer 20 uses the unmodulated light as local oscillation light to perform homodyne detection of the modulated light and outputs the detection result as an electric signal.
WATANABE TATSU
TANAKA HIDEAKI
SUZUKI MASATOSHI
HORIUCHI YUKIO
