| 摘要 |
PURPOSE:To improve the reliability and to decrease the loss of a signal light by synthesizing a signal light of optional polarized wave and a local oscillation light of circularly polarized wave, separating them into orthogonal linear polarized wave and detecting it and connecting optical elements by an optical fiber to be connected while the plane of polarization is maintained. CONSTITUTION:The light of a signal laser 1 is propagated through the optical fiber 2 and made incident in an optical fiber pi/2 phase shift coupler 13 in an optional polarized wave state. Then the local light having a linearly polarized wave in a fixed direction from the local oscillation laser 5 is subject to rotation of polarized direction so as to be made coincident with the specific direction of the coupler 13 while preserving the polarized wave front by a plane of polarization preserving optical fiber 14-1 and made incident in the coupler 13. The said signal light and local light are led to a polarized demultiplex element 3 via a single mode optical fiber 17, demultiplexed into orthogonal polarized components and made incident in the optical receivers 8a, 8b. Moreover, the plane of polarization preserving optical fibers 14-1, 14-2, 14-3 and the laser 1 are connected between the laser 1 and the coupler 13, between a laser 5 and the coupler 13, between the element 3 and the receiver 8a and between the element 3 and the receiver 8b to improve the reliability of the system. Since the polarized wave of the light is the circularly polarized wave at the emitting end of the coupler 13, even if the element 3 give demultiplexing to the orthogonally polarized wave, the polarization is made coincident with the orthogonal polarized component of the signal light without fail, and no loss is given to the signal light. |
