Patent ID: 7961392

Claim:
A polarization beam splitter for polarization-splitting incident light when light to undergo polarization-splitting has an incidence angle that falls in a range of 54 degrees through 66 degrees, the polarization beam splitter comprising, between two transparent substrates: an adhesive layer configured to adhere to one of the two transparent substrates; two or more types of dielectric multilayer films each having a different corresponding design basis wavelength, the two or more types of dielectric multilayer films each including high refractive index films and mid refractive index films, the high refractive index films and mid refractive index films each having an optical thickness in accordance with the corresponding design basis wavelength and being alternately laminated to form an even number of layers; a single-layer dielectric film, the single-layer dielectric film contacting a last layer in a last of the two or more types of dielectric multilayer films, the single-layer dielectric film being the same as a first layer in the last of the two or more types of dielectric multilayer films; two sandwich-use mid refractive index films, the two or more types of dielectric multilayer films and the single-layer dielectric film being sandwiched between the two sandwich-use mid refractive index films, the sandwich-use mid refractive index films each having an optical thickness corresponding to a wavelength λ that is distinct from any of said design basis wavelengths; and the two or more types of dielectric multilayer films and the single-layer dielectric film and the two sandwich-use mid refractive index films form a polarization split film, which performs a polarization split function with respect to light that is substantially in the visible wavelength region.