| 主权项 |
1. A planar optical system (10) for wide field-of-view polychromatic imaging, consisting essentially of:
a planar waveguide (3) consisting exclusively of a plate having two faces (4, 5) that are plane and parallel, said planar waveguide having a thickness of the order of 1 mm; an entry coupler consisting exclusively of a first diffraction grating (1); an exit coupler consisting exclusively of a second diffraction grating (2); the planar optical system (10) being adapted to receive an incident optical beam (6, 16) having an optical spectrum of spectral width Δλ and an angular field ±Δθ and defining a mean angle of incidence i0 with the normal to a face (4, 5) of the waveguide (3); said first diffraction grating (1) being adapted to couple said incident beam (6, 16) into the planar waveguide (3) as a beam (7, 17) adapted to propagate in the waveguide (3) by total internal reflection at the faces (4, 5) of the waveguide (3), and the second diffraction grating (2) being adapted to receive the coupled beam and to diffract said coupled beam out of the waveguide as an exit beam (9, 19); characterized in that: the first and second diffraction gratings (1, 2) are diffraction gratings of low line density, having a pitch greater than the wavelength of use over a spectral range at least from 450 nm to 630 nm, the line density of the said first and second diffraction gratings (1, 2) being less than 1200 lines/mm, the waveguide (3) is in a transparent material, and the refractive index of the waveguide (3) is at least 1.55 and less than 1.65 over said spectral range at least from 450 nm to 630 nm, the first diffraction grating (1) is adapted to couple an entry beam (6, 16) over said spectral range of at least 450 nm to 630 nm, of mean angle of incidence i0 in the range 30 degrees to 60 degrees and having an angular field 2*Δθ of ±15 degrees into the waveguide (3) by positive first order (+1) diffraction, said coupled beam (7, 17, 8, 18) defining an internal angle of incidence greater than the angle of total internal reflection and less than a limit angle γ, the limit angle γ being 80 degrees and the second diffraction grating (2) being adapted to receive the coupled beam (7, 17, 8, 18) and to diffract the coupled beam by negative first order (−1) diffraction out of the waveguide (3) at a mean exit angle i1 relative to the normal to an exit face (4, 5) of the waveguide (3) in the range 30 degrees to 60 degrees over said spectral range of at least 450 nm to 630 nm, and the planar optical system (10) provides wide field-of-view polychromatic imaging over said spectral range at least from 450 nm to 630 nm. |
