| 摘要 |
PURPOSE:To improve the characteristics of transmission and reflection by providing the beam splitter with a plane transparent plate having some refractive index, a low refractive index film layer having higher refractive index than the transparent plate and a high refractive index film layer having higher refractive index than the former film layer. CONSTITUTION:The beam splitter is formed by laminating the 1st layer consisting of the low refractive index film layer (refractive index NL, film thickness lambdaO/4) and the 2nd layer consisting of the high refractive index film layer (refractive index NH, film thickness lambdaO/4) successively up to the Nth layer and forming the low refractive index film layer on the highest Nth layer. If the beam splitter is to be used for an optical disc reproducing optical system using a near infrared-ray laser oscillator, the conditions of refractive indexes to satisfy the request are shown in the table at the film constitution of e.g. 3-9 layers. In accordance with the spectral characteristics of P and S polarizing components constituted by the number of layers based upon the table, a beam splitter having 50% transmittivity is obtained independently of the number of layers. |
