| 摘要 |
PURPOSE:To use a polarized wave controller whose control circuit and optical system are simple, and also, to always make the polarized wave state of a signal light and a local oscillation light coincide, by providing a birefringence generating part for converting the output light of a local oscillation light source to a linearly polarized wave having a desired main axis. CONSTITUTION:The signal light of an optical transmission line 1 outputted to the light output terminal 5 of an optical coupler 2, and the output light of a local oscillation light source 6 are brought to an optical heterodyne detection in an optical heterodyne detector 11. In this state, the FSK signal of 600MHz intermediate frequency, and 200Mb/s bit rate are fetched. This detecting signal is amplified by an amplifying circuit 12, and a voltage is applied to a polarized wave controller 9 by a driving power source 13, by what is called 'a mounting climbing method' by which its output signal always becomes maximum. In this case, the output light of a linearly polarized wave outputted from the local oscillation light source 6 becomes a linearly polarized light even in the light output terminal of a single mode optical fiber 8 by a birefringence giving part 10. In this way, the polarized wave controller 9 can always make the output light of the local oscillation light source 6 coincide with the polarized wave state of a signal light varied in the course of transmission, and an optical heterodyne detection of the maximum output can be executed.
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