Patent ID: 6791750
Filing Date: 2004-09-14
Classification: G02B

Abstract:
A polarization beam splitter comprising:a first prism including a first surface on which light is incident and a second surface that makes an acute angle with the first surface; a second prism disposed so as to face the second surface of the first prism; and a dielectric multilayer film sandwiched between surfaces of the first and second prisms that face each other and composed of: a first multilayer portion having high-refractive-index layers and low-refractive-index layers laid alternately on one another so that each layer has an optical film thickness equal to {fraction (1/4 )} of a first wavelength; and a second multilayer portion having high-refractive-index layers and low-refractive-index layers laid alternately on one another so that each layer has an optical film thickness equal to Â¼ of a second wavelength, wherein, let the first wavelength be &lgr;1, the second wavelength be &lgr;2, and an angle that the first and second surfaces of the first prism make with each other be &thgr;, then the condition &lgr;12&lE;1.55Â·&lgr;1is fulfilled, and in addition, let a refractive index of the first prism be Nd, a refractive index of the high-refractive-index layers of the first multilayer portion be NH1, a refractive index of the low-refractive-index layers of the first multilayer portion be NL1, a refractive index of the high-refractive-index layers of the second multilayer portion be NH2, and a refractive index of the low-refractive-index layers of the second multilayer portion be NL2, then, for angles &thgr;1 and &thgr;2 that respectively fulfill sin2&thgr;1=NH12Â·NL12/[Nd2Â·(NH12+NL12)] and sin2&thgr;2=NH22Â·NL22/[Nd2Â·(NH22+NL22)], the conditions|NH1âˆ’NL1|NH2âˆ’NL2| and |&thgr;1âˆ’&thgr;|2âˆ’&thgr;|, or |NH1âˆ’NL1|>|NH2âˆ’NL2| and |&thgr;1âˆ’&thgr;|>&thgr;2âˆ’&thgr;|are fulfilled.