| 摘要 |
An optical hybrid circuit includes a MMI coupler including a pair of input channels provided at positions symmetrical with respect to a center position in a widthwise direction thereof, a pair of first output channels outputting a pair of first optical signals having an in-phase relationship, and a pair of second output channels neighboring with each other outputting a pair of second optical signals having an in-phase relationship. The MMI coupler converts QPSK signal light or DQPSK signal light into the pair of first optical signals and the pair of second optical signals having an in-phase relationship. The optical hybrid circuit includes a 2:2 optical coupler connected to the first or the second output channels. The 2:2 optical coupler converts the pair of first optical signals or the pair of second optical signals into a pair of third optical signals having a quadrature phase relationship with the pair of first or second optical signals.
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