| 摘要 |
PROBLEM TO BE SOLVED: To obtain a three-port optical circulator which is such a complete circulation type that light inputted from a 3rd port returns to a 1st port. SOLUTION: A 1st birefringent element 10 for demultiplexing and multiplexing which demultiplexes light beams of the same optical path having their polarization directions orthogonally and multiplexes light beams of different optical paths, a 1st polarization rotating means 12 which converts orthogonal polarization directions to orthogonal directions or vice versa, a circulator function part 14, a 2nd polarization rotating means 16, and a 2nd birefringent element 18 for demultiplexing and multiplexing are arranged in this order. The circulator function part is equipped with a 1st birefringent element 20 for optical path control which shifts the optical paths according to the polarization directions, a 2nd birefringent element 22 for optical path control which has an optical shift quantity twice as large as that of the 1st element, and a 1/4- wavelength plate 24 and a reflection body 26 which are positioned between those 1st and 2nd birefringent elements for optical path control and operate on only the light of the center optical path while the light beams of side optical paths bypass them.
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