Achromatic flat-panel display
View Patent ↗An achromatic flat-panel projection display comprises a video projector 2 a , a condensing lens ( 26 ) and a tapered transparent slab spreading the image input from the projector over the area of th slab. To compensate for dispersion in the slab a dispersive prism is used at the input edge of the slab, whose dispersion cancels out the dispersion of the slab. The prism can be a separate part of simply a bevel in the input edge, i.e. the thick end of the slab.
1. An achromatic flat-panel projection display comprising an image projector for projecting an image to be displayed, and a tapered transparent slab into the thick end of which the image is projected so that the rays emerge over one face of the slab, the slab being made of a dispersive material; further comprising a dispersive prism between the projector and the slab, compensating for the dispersion occurring in the slab.
2. A display according to claim 1 , in which the prism is a separate component.
3. A display according to claim 2 , in which the prism is made of the same material as the slab.
4. A display according to claim 1 , in which the prism is integral with the slab so that the input edge is bevelled.
5. A display according to claim 1 , in which the angle β of the prism satisfies
sin
(
θ
1
+
β
)
tan
β
=
n
0
2
-
sin
2
(
θ
1
+
β
)
-
(
n
0
2
-
1
)
n
0
2
-
sin
2
(
θ
1
+
β
)
where θ 1 is the angle of input in air relative to the plane of the slab, and n 0 is the average refractive index of the material of the slab over the range of wavelengths input from the projector.