| 摘要 |
PURPOSE:To decrease the fluctuation in a light transmission characteristic by thermal stress by providing a compensation film having the coefft. of thermal expansion approximately equal to the coefft. of thermal expansion of a waveguide film formed on the front face of a substrate to the rear face of the substrate. CONSTITUTION:The film to service as the compensation layer 5 having the coefft. of thermal expansion approximately equal to the coefft. of thermal expansion of the film formed on the front face is formed on the rear face of the substrate 1. Namely, the coefft. of thermal expansion distribution is approximately symmetrical with about the middle in the thickness direction of the substrate 1 as a center and, therefore, the substrate 1 is not warped by a temp. fluctuation. Since there is no change in the size of the structure, the light transmission characteristic does not fluctuate and since the substrate does not warp at the time of a high-temp. heat treatment, the light propagation characteristic is not deteriorated. Furthermore, the coefft. of thermal expansion distribution is approximately symmetrical with about the middle in the thickness direction of the substrate 1 as a center and, therefore, even if, for example, the thermal stresses are generated, these stresses are also symmetrically distributed. The anisotropy of the refractive index is thereby greatly decreased. |
