| 摘要 |
PURPOSE: To provide a beam splitter which is 22.5 deg. in ray incident angle and has a low dependency of branching ratios on polarized light. CONSTITUTION: This beam splitter is formed by laminating plural optical films 2 on a glass substrate 1 having a refractive index of 1.51±0.10. The refractive indices and optical film thicknesses of the respective optical films 2 are as follows in order nearer the substrate 1: The refractive index of the first layer is 1.44±0.10 and the optical film thickness thereof is 0.05 to 0.15, the refractive index of the second layer is 1.68±0.10 and the optical film thickness thereof is 0.01 to 0.10, the refractive index of the third layer is 1.44±0.10 and the optical film thickness thereof is 0.50 to 0.60, the refractive index of the fourth layer is 2.23±0.10 and the optical film thickness thereof is 0.25 to 0.35 and the refractive index of the fifth layer is 1.44±0.10 and the optical film thickness thereof is 0.25 to 0.35. The optical film thickness is the relative value expressed by n×d/λwhere the refractive index is defined as (n), the actual film thickness as (d) and the wavelength to determine the center of the band asλ.
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