Patent ID: 6522473
Filing Date: 2003-02-18
Classification: G02B

Abstract:
An optical system, interposed between a pupil plane and an image plane, comprising:a first prism; a second prism; and a holographic element sandwiched between said first prism and said second prism, cemented to these prisms, wherein when a light beam traveling along an optical path connecting said pupil plane and said image plane through said optical system is called a first beam, said first prism has a 1-1 surface placed on a pupil side, combining a function of transmission with a function of reflection of said first beam; a 1-2 surface placed on an opposite side of a pupil with respect to said 1-1 surface; and a 1-3 surface placed on an image side, transmitting said first beam, said second prism includes a 2-1 surface having a shape identical with said 1-2 surface, placed opposite thereto to transmit said first beam at least twice, and a 2-2 surface placed on the opposite side of the pupil with respect to said 2-1 surface of said second prism, reflecting said first beam, said holographic element is constructed so that said first beam, when entering said holographic element at a first incident angle, is diffracted and reflected and when entering said holographic element at a second or third incident angle, is transmitted, and thereby said 1-2 surface of said first prism combines a function of transmission with a function of reflection of said first beam, and said 1-1 surface of said first prism is configured as a totally reflecting surface such that when said first beam is incident on said 1-1 surface at an incident angle over a totally reflecting critical angle, said first beam is reflected, while when said first beam is incident at an incident angle below said critical angle, said first beam is transmitted, and thereby said 1-1 surface combines a function of reflection with a function of transmission.