| 摘要 |
PROBLEM TO BE SOLVED: To solve such a problem that control of the relation between the film thickness and the refractive index has been difficult by conventional methods in an optical filter of a refractive index gradient type in which the refractive index differs in the film thickness direction. SOLUTION: A plurality of vitreous composite target materials 7a, 7b and so on containing a plurality of metal elements and oxygen are disposed while varying the compounding ratio of the metal elements for every target material. The composite target materials are successively sputtered by using a common ion gun 2 so that vitreous films with the refractive index varying stepwise can be successively deposited on the surface of a substrate 3 with high accuracy.
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