Optical system
An optical system includes a display, at least one lens, and at least one of a partial reflector and a reflective polarizer. The optical system forms a virtual image of an image emitted by the display for viewing by an eye. The emitted image includes a plurality of cones of image light. Each cone of image light propagates from a different corresponding location on the emitted image and includes a central light ray propagating along a central axis, such that in each of orthogonal first and second planes that include the central axis, an intensity distribution of the cone of image light as a function of angle relative to the central axis includes a substantially flat peak having a full width of at least 15 degrees across which the peak changes by less than about 20%, and a corresponding fullwidth at half maximum that is less than about 60 degrees.
1 . An optical system centered on an optical axis and comprising:
an aperture stop;
a display panel configured to generate an image, the optical system configured to display a virtual image of the generated image to an eye of a viewer disposed on the optical axis proximate the aperture stop;
an illumination source configured to provide illumination to the display panel from an emission surface of the illumination source, the emission surface of the illumination source comprising a plurality of locations, a cone of light emitted through each location of the plurality of locations on the emission surface of the illumination source comprising a central light ray propagating along a direction parallel to the optical axis and having a peak intensity and corresponding full widths W80 and W30 at respective eighty and thirty percent of maximum, W80 and W30 within about 30% of each other;
a light redirecting film disposed between the display panel and the emission surface of the illumination source and comprising a regular array of light redirecting elements configured to receive, transmit, and redirect at least some of, the cones of light emitted through the emission surface of the illumination source so that the transmitted cones of light cover the display panel and are transmitted thereby as corresponding cones of image light; and
a lens assembly disposed between the display panel and the aperture stop and comprising at least one of a lens, a partial reflector, and a reflective polarizer, such that the cones of image light pass through the aperture stop after going through the lens assembly.
2 . The optical system of claim 1 , wherein the central light ray of each cone of light emitted through each location of the plurality of locations on the emission surface of the illumination source makes an angle of less than about 5 degrees with the optical axis.
3 . The optical system of claim 1 , wherein each of the transmitted cones of light transmitted by the light redirecting film has a peak intensity and corresponding full widths W′ 80 and W′ 30 at respective eighty and thirty percent of maximum, W′ 80 and W′ 30 within about 30% of each other.
4 . The optical system of claim 1 , wherein each of the cones of image light comprises a flat peak having a full width of at least 15 degrees across which the peak changes by less than about 20%, and a corresponding fullwidth at half maximum that is less than about 60 degrees.
5 . The optical system of claim 1 , wherein the lens assembly comprises at least one lens, a partial reflector, and a reflective polarizer, each of the cones of image light passing through the aperture stop after going through each of the at least one lens, the partial reflector, and the reflective polarizer.
6 . The optical system of claim 5 , wherein each of the cones of image light passes through the aperture stop after further being reflected at least once by each of the partial reflector and the reflective polarizer.
7 . The optical system of claim 1 , wherein the emission surface of the illumination source is smaller in a length and a width than the display panel.
8 . The optical system of claim 1 , wherein the regular array of light redirecting elements comprises facets of a Fresnel lens.
9 . The optical system of claim 1 , wherein the aperture stop has a size of between about 1 mm and about 10 mm.
10 . The optical system of claim 1 , wherein the lens assembly comprises at least one lens.
11 . The optical system of claim 1 , wherein the lens assembly comprises a partial reflector, such that for a normally incident light and for each of mutually orthogonal polarization states, the partial reflector reflects at least 40% of the incident light and transmits at least 40% of the incident light.
12 . The optical system of claim 1 , wherein the lens assembly comprises a reflective polarizer, such that for a normally incident light, the reflective polarizer reflects at least 60% of the incident light polarized along a first in-plane direction and transmits at least 60% of the incident light polarized along an orthogonal second in-plane direction.
13 . The optical system of claim 1 further comprising a retarder layer, such that for a central light ray of at least one of the cones of image light, the retarder changes a phase of the central light ray by at least 20 degrees.