Patent ID: 7454103
Filing Date: 2008-11-18
Classification: G02B,G03H

Abstract:
1. An optical diffraction device comprising: a layer defining a general plane and arranged for propagating locally at least one local leaky mode which is excited by refraction of a locally incident electromagnetic wave having a given vacuum wavelength λ and reaching said layer from a cover medium of refractive index n a highly reflective structure at the lower side of said layer for said at least one local leaky mode; a diffractive element in the form of a corrugation or/and of an index modulation arranged in, or/and at the upper side of, or/and above, or/and at the lower side of, or/and under said layer for diffracting said locally incident electromagnetic wave into the reflected −1 said locally incident electromagnetic wave reaching said layer with a local incidence direction defining together with said normal to the general plane a local incidence plane, said diffractive element having a local grating vector K g making an angle β with said local incidence plane which is larger than or equal to zero and smaller than or equal to 90 degrees, the diffractive element having, where said locally incident electromagnetic wave reaches said layer, no positive propagating diffraction order and all negative propagating orders with substantially zero diffraction efficiency except the −1 st order when said angle β is smaller than 90 degrees and all propagating diffraction orders except the two first diffraction orders with substantially zero diffraction efficiency when said angle β is equal to 90 degrees, wherein the diffraction device comprises a semi-reflective structure for said locally incident electromagnetic wave which is arranged between the upper side of said layer and said cover medium, this semi-reflective structure being arranged for increasing the −1 st order diffraction efficiency when said angle β is smaller than 90 degrees and the two first diffraction order efficiencies when said angle β is equal to 90 degrees.