Patent ID: 6504660
Filing Date: 2003-01-07
Classification: G02B

Abstract:
A prism comprising:a first portion made of a first material having a wavelength dependency in a refractive index; and a second portion abutting to the first portion, the second portion being made of a second material having a wavelength dependency in a refractive index which is different from the wavelength dependency in the refractive index of the first material, wherein the first portion and the second portion have shapes such that the wavelength dependency in the refractive index of the first portion and the wavelength dependency in the refractive index of the second portion are substantially cancelled by each other and the prism is a reflective-type prism including a reflecting portion within a light path from an external incident light of a light beam to an emitting light as a shaped light beam, wherein a surface A denotes a surface of the first portion on which the external incident light is incident, a surface B denotes a joint surface between the first portion and the second portion, and a surface C denotes a surface of the second portion facing the surface B; the light path of the reflective-type prism is such that the external incident light is incident on and refracted at the surface A, the light refracted at the surface A is incident on and refracted at the surface B, the light refracted at the surface B is incident on and reflected by the surface C, the light reflected by the surface C is again incident on and refracted a second time at the surface B, and the light refracted at the surface B is again incident on and refracted a second time at the surface A, and thereby supplied to the outside of the prism as the emitting light, wherein the wavelength dependency in the refractive index of the second material is larger than the wavelength dependency in the refractive index of the first material; wherein the prism spatially magnifies the emitting light with respect to the external incident light so as to shape the light beam by providing the spatial light intensity distribution of the emitting light to be different from the spatial light intensity distribution of the external incident light; wherein the magnification of the emitting light is defined by four refractions which are the two refractions at each of surfaces A and B; and wherein a plurality of angles made by normals to the surfaces A, B and C with respect to an incident direction of the external incident light on the surface A are &pgr;/2âˆ’&agr;1, &pgr;/2âˆ’&agr;2 and &pgr;/2âˆ’&agr;3, respectively; a relationship &agr;2>&agr;3>&agr;1 is satisfied, wherein &agr;1, &agr;2 and &agr;3 are angles made by the surfaces A, B and C with respect to the incident direction of the external incident light, respectively.