| 摘要 |
PURPOSE:To realize the transmission system immune to external disturbance by making wavelengths of two lasers at the transmission side equal, providing a time width for identifying a channel to the same time for both channels at a prescribed period, sending one laser light only in the time width only and providing a polarized wave compensating device to the reception side. CONSTITUTION:The wavelengths generated from lasers 1-1, 1-2 are equal. In modulation, the identification signal time width 22 is provided periodically to modulated light 3-1, 3-2 in addition to a transmission signal time width 21 and only one side modulated light 3-1 is made always incident in a optical fiber within the time width. The polarized wave of the modulated light 3-1, 3-2 enters a polarized wave compensation device 6 via an optical fiber 5. The light 7 subject to polarized wave compensation is separated into orthogonal linearly polarized wave reception light 9-1, 9-2 and converted into electric signals 11-1, 11-2. The signal 11-1 is coincident with the signal waveform of the light 3-1. A part of the signal light 11-1 is led to a synchronizing signal generating circuit 12 to obtain a synchronizing signal 13 synchronously with the identification signal. A feedback circuit 14 detects the level of the signal 11-2 at generating the synchronizing signal 13 to control the polarized wave compensating device 6 thereby minimizing the level. Thus, the fluctuation of the polarized wave due to external disturbance onto the optical fiber is suppressed. |
