Patent ID: 6757105
Filing Date: 2004-06-29
Classification: G02B

Abstract:
A diffractive optical element for trapping and propagating a light having a color spectrum characterized by a plurality of wavelengths longer than a shortest wavelength, &lgr;B, and shorter than a longest wavelength &lgr;R, the light striking the diffractive optical element at an angle greater than a first field-of-view angle, &agr;âˆ’FOV, and smaller than a second field-of-view angle, &agr;+FOV, the diffractive optical element comprising a linear grating being formed in a light-transmissive substrate, wherein:(a) said linear grating is characterized by a pitch, d, selected so as to allow total internal reflection of a first light ray having wavelength of &lgr;B and a striking angle of &agr;âˆ’FOV, thereby to trap said first light ray by total internal reflection; (b) said light-transmissive substrate is characterized by an index of refraction, ns, larger than a minimal index of refraction, nMIN, said minimal index of refraction is selected so as to allow total internal reflection of a second light ray having wavelength of &lgr;R and a striking angle of &agr;+FOV, thereby to trap said second light ray by total internal reflection; and (c) a thickness of said light-transmissive substrate is sufficiently large so as to allow propagation of a light of any wavelength longer than &lgr;B and shorter than &lgr;R, striking said light-transmissive substrate at any angle larger than &agr;âˆ’FOV and smaller than &agr;+FOV.