This invention regards the planer light wave circuit which includes the concave reflected type diffraction grating where 1 pair the identical focus line which separates the 1st and 2nd throb guided wave road territory is shared oppose. The light which was induced one side of the diffraction grating or by both is forwarded, in order to receive, the end of the input and output guided wave road, is arranged alongside the focus line. With this invention, it forwards the light inside the fixed wave length range from the input guided wave road, induces with the single diffraction grating, it becomes possible to output to the guided wave road which is inside all single throb guided wave road territories light inside another wave length range is sent, directing to another diffraction grating from a certain diffraction grating, is output to the guided wave road inside the throb guided wave road territory which differs.
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