| 摘要 |
PURPOSE:To eliminate the lowering and irregularity in light transmissivity, and to improve the yield in a flame detector requiring a bent optical axis, by using a metal coated optical fiber as the optical fiber of a light guiding part. CONSTITUTION:An Al coated optical fiber 21 is inserted in a stainless steel pipe 20 and mechanical plastic deformation is applied to the pipe 20 to form a bent optical fiber 18. If the inner diameter of the pipe 20 is set to 130-150% of the outer diameter of the Al coated optical fiber 21, the bending angle thetaof 50-60 deg. can be realized by the mechanical bending of the pipe 20 without damaging the fiber 21. By this constitution, because the lowering in light transmissivity is purely caused only by an increment in light transmission loss due to mechanical bending and there is no increase in light transmission loss due to heat processing, the lowering in the light transmissivity is reduced. Further, because the lowering and irregularity in light transmissivity due to mechanical bending is extremely low as compared with that due to thermal bending processing, there is no obstacle in a flame detector and the lowering in the yield of a product is not generated at all.
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