| 摘要 |
Optical filter with a thin film form by laminating low refractive index layers (20) alternately from substrate side (18) with high refractive index layers (21). The thin film is provided with first, second and third laminated portion (22-24). In the first laminated portion (22), the refractive indices of the high refractive index layers become gradually higher, while in the second laminated portion (23) the refractive index of the higher refractive index layers remain substantially equal to the highest refractive indices of the high refractive index layers of the first laminated portion. In the third laminated portion (24), the refractive indices of the high refractive index layers become gradually lower. The refractive indices of the low refractive index layers in the first through third laminated portions are substantially equal to the refractive index of the substrate. An absolute value of the refractive index gradient of the high refractive index of the first laminated portion is not the same as in the third laminated portion.
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