| 摘要 |
PROBLEM TO BE SOLVED: To make reducible or preventible the loss of light caused by the diffusion of a light diffusing part. SOLUTION: Light transmitted an entrance side optical fiber 14 outgoes from the optical fiber 14 at the diffusing angle A=18.7 degrees, then enters a light diffusion part. When parallel light enters the light diffusing part 18, the parallel light is diffused into the diffusing angle B=20 degrees by the diffusing characteristics of the Gaussion distribution. When the difussion light of the diffusing angle A=18.7 degrees enters the light diffusing part 18, the diffusing light is further diffused into the diffusing angle 27.3 degrees. Hereupon, since the angle C decided by the numerical aperture NA of an entrance side optical fiber 16 is set to 27.3 degrees or more, light diffused by the light diffusing part 18 is totally reflected within the optical fiber 16.
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