| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical fiber coupler giving light branching and coupling directivity and its production method. SOLUTION: Althought signal light made incident from the core 31a of a coupling area 31a on the core 41a if a coupling area 41 through a boundary face 51 is partially reflected, the remaining light is refracted and made incident on the core 41a of the area 41. On the other hand, signal light having a progress angle smaller than a progress angle ofπ/2-θcorresponding to the critical angleθof the boundary face 51 out of signal light beams made incident on the core 31a of the area 31 is totally reflected and is not made incident on the core 31a. Thereby, the coupling of signal light between both the coupling areas 31, 41 can be provided with directivity.
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