| 摘要 |
PURPOSE:To perform reproduction with a little S/N deterioration due to a phase shift by using one light wave separated by a polarization separator as a light wave for a local oscillator when modulated information of a coherent light wave is demodulated. CONSTITUTION:Single polarized wave coherent light from an optical fiber 1 which contains optically phase-modulated information is made into circular polarized light by a lambda/4 plate 2 and this light is separated by the polarization separation device 3 into polarized light waves having mutually orthogonal polarization directions. One is shifted in phase by 90 deg. through a lambda/2 plate 5 to obtain the same polarization direction with the other polarized light wave, and then made incident on a lens 6. The other wave is reflected 10 totally by an optical phase modulator 14 and made incident to the lens 6, but phase-modulated optically by an oscillator 1 at the frequency from an oscillator with optical path length variation. Those two polarized waves incident on the lens 6 are multiplexed and photodetected 7, and a signal of frequency after the optical phase modulation of the optical phase modulator 14 at the frequency of the oscillator 8 is extracted and inputted to a mixer 9. The mixer 9 mixes it with the frequency of the oscillator 8. Consequently, reproduction with good S/N is attained. |
