| 摘要 |
A blocking portion is provided at an end of the mirror to prevent a light beam emitted from an input port from being transmitted to or reflected by first and second output ports. The mirror is inserted to a position where the end of the blocking portion of the mirror reaches a boundary P2' on the insertion side of an area to be blocked to obtain a permissible crosstalk value of the light beam. The mirror is removed to a position where the rear end of the blocking portion of the mirror reaches a boundary P2 on the removal side of the area to be blocked. The mirror is movably driven between the removal position and the insertion position in the optical path of a first light beam by a drive. Thus it is possible to reduce the length of the driving stroke of the mirror.
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