| 摘要 |
PURPOSE:To improve the performance of an optical filter and to reduce the production cost of the filter by forming a vapor deposition layer as the outermost surface layer to have a two-layered structure having distribution of compsn. and refractive index in the direction of the film thickness. CONSTITUTION:A glass layer 6 formed as the outermost surface layer of multilayered film is formed by vapor-deposition SiO2 in a same cell without introducing reactive gas continuously. The refractive index of the glass layer 6 obtd. in this stage is n 1.50-1.53 and the compsn. of the glass is expressed by SiOx (where x=1.5-<2.0). The film thickness of the glass layer 6 is regulated to ca. 1mum with the purpose for preventing deterioration of optical properties of the filter. Further, SiO is vapor-deposited by resistance heating vapor- deposition forming SiO film having optical film thickness corresponding to 1/2 wavelength on the outermost surface layer (glass layer 6) with the purpose for obtd. reflection reducing effect. The refractive index of the reflection reducing layer 7 is n 1.80-1.85.
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