Patent ID: 7652823

Claim:
A non-polarizing beam splitter comprising: a first prism; a ground layer made of a dielectric material which is formed on a slant face of the first prism; an Au layer having thickness of 15.5 to 35 nm which is formed on the ground layer; a protective layer made of a dielectric material which is formed on the Au layer; and a second prism which is jointed to an outermost layer of the protective layer via adhesive, wherein the non-polarizing beam splitter divides light at wavelength of 640 nm to 820 nm into transmission light and reflection light by a predetermined ratio, wherein the following conditions are satisfied: 25.2X 2 +12.4X+6.84<D<31.6X 2 .+12.6X+10.4, R+T>88 (%) where, X=R /( R+T ) R designates an average of reflectance of P polarized light and reflectance of S polarized light at the wavelengths of 640 nm to 680 nm and 760 nm to 810 nm, T designates an average of transmittance of the P polarized light and transmittance of the S polarized light at wavelengths of 640 nm to 680 nm and 760 nm to 810 nm, D designates a thickness of the Au layer (nm).