| 摘要 |
PROBLEM TO BE SOLVED: To ensure a constant quantity of light without being influenced by scattering in outer diameters of monitor optical fibers and optical axes of optical source lamps by forming a light leakage part on the whole outer circumference of light guide at an incident end of thereof, and fitting a ring-shaped monitor fiber on the light leakage part. SOLUTION: A light leakage part 3 is formed over the whole outer circumference of a light guide 2 so as to monitor the quantity of light at an incident end 2a of the guide 2. The formation of the part 3 may be done by scrubbing the clad surface of an optical fiber on which the guide 2 is formed to give flaws thereto. For the reception of light from the part 3, a ring-shaped monitor fiber 4 corresponding to the outer diameter of the guide 2 at the portion of the part 3 and the formation width of the part 3 is fitted. The width of the fiber 4 should be formed slightly wider than the formation width of the part 3 so as to prevent leakage of light from the part 3 to the outside.
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