To prevent dew condensation in fiber type optical parts and to prevent changes in the optical characteristics by forming a part of a protective case to house and seal the optical parts body from a specified high moisture permeable resin.
A part of a protective case consists of a high moisture permeable resin having a moisture permeation coefficient of ≥140 g/m2/24 hour. The high moisture permeable resin having a moisture permeation coefficient of ≥140 g/m2/24 hour, such as silicone resin is used for the sealing resin 4. If the moisture permeation coefficient is less than 140 g/m2/24 hour, the moisture in the parts is not smoothly discharged, and the effect to prevent dew condensation can not be obtained. If the high moisture permeable resin has good mechanical characteristics, not only the sealing resin 4 is formed from the high moisture permeable resin, but the whole or a part of the protective pipe 2 can be formed from the aforementioned high moisture permeable resin. The proportion of the high moisture permeable resin in the protective case 5 is preferably about ≥2% of the whole surface area, and if the resin has higher moisture permeation coefficient, the proportion may be smaller than the aforementioned value.
NISHIDE KENJI
YAMAUCHI RYOZO
