| 摘要 |
PURPOSE:To extend a band width by defining a thickness of an optical film at a center layer or its adjacent layer of a dielectric multilayer film so as to be the max. band width in a specific range. CONSTITUTION:In the title film formed on an optical substrate having 1.45-1.65 refractive index, the dielectric mutlilayer film having a film formation shown by the formula {(0.5H)L(0.5H)}<k> (k = a natural number) wherein H and L are each thickness of the optical films composed of the materials having a high and a low refractive index respectively, the thickness of the optical film at the center layer is defined so as to be the max. band width in the thickness (d) of the optical film having 0.7-2.0lambda range, thereby enabling to obtain a large band width and to obtain a sufficiently broad band width in the polarized light separation, even if the title film of a low cost is used.
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