| 摘要 |
PURPOSE:To realize a stable optical heterodyne communication without generating an instantaneous disconnection, by controlling the branching ratio of the first and second optical branching devices and the driving circuits of the first and second polarized light control elements, so that a branching ratio of the first and second optical couplers is varied continuously. CONSTITUTION:When a value of at least one of driving voltages V1l of the first polarized light control element 504A becomes >=V1l<max>-DELTAV (DELTAV>0) or becomes V1l<max>+DELTAV, by the variation of a polarized light state of a signal light, a control part 508 varies continuously the branching ratio of the first optical coupler 507A side and second optical coupler 507B of the first and second optical branching devices 502, 503, to '0':'1' through a state of (1-x):x (0<x<1) from '1':'0'. The driving voltage V2l of the second polarized light control element 504B is always in a state for converting the polarized light state of the signal light so that it coincides with a polarized light state of a local oscillation light. Accordingly, from the time point when a part of the signal light is made incident on the second polarized light controlling circuit 506B from the branching device 502, the signal light is converted stably without generating an instantaneous disconnection, so that its polarized light state coincides with a polarized light state of the local oscillation light. |
