Prism having two inner surfaces and outer shape regarded as plane parallel plate

摘要

A prism (1) comprises a first inner surface (114A) that performs total reflection of all rays (20) entering from the exterior and allows ON light (21) to pass therethrough; a second inner surface (122) that allows the rays (20) and the ON light (21) to pass therethrough and performs total reflection of OFF light (22); and a third inner surface (134) that allows the ON light (21) to pass therethrough. A first end (1E1) of the first inner surface (114A) is located in proximity to and above a predetermined point (P) in the second inner surface (122). The prism (1) is regarded as a plane parallel plate having a second outer surface (121) and a third outer surface (133).