Optical system with compact coupling from a projector into a waveguide
An optical system includes a light-guide optical element (LOE) ( 10 ) having mutually-parallel first and second major external surfaces ( 11, 12 ) for guiding light by internal reflection, and a projector ( 100 ) that projects illumination corresponding to a collimated image from an aperture ( 101 ). The projector injects light in to the LOE via a coupling prism ( 30 ) attached to the first major external surface ( 11 ) that projects an image injection surface. A reflective polarizing beam splitter ( 51 ) is deployed at an interface between the major external surface ( 11 ) and the coupling prism ( 30 ) parallel to the major external surfaces, to selectively transmit illumination from the coupling prism into the LOE while trapping light already within the LOE so as to propagate within the LOE by internal reflection.
1. An optical system comprising:
(a) a light-guide optical element (LOE) formed from transparent material and having mutually-parallel first and second major external surfaces for guiding light by internal reflection;
(b) a projector configured to project light corresponding to a collimated image from an aperture, the light exiting said aperture with a chief ray defining an optical axis of said projector and with an angular field about the chief ray;
(c) a coupling-in arrangement associated with said projector and with said LOE for coupling said light from said projector into said LOE at a coupling-in region so that the light undergoes internal reflection at said major external surfaces, said coupling-in arrangement including a reflective polarizing beam splitter and a waveplate deployed such that, for at least one part of said angular field, the light propagating within said LOE has spatial non-uniformity of polarization;
(d) a coupling-out arrangement associated with said LOE for redirecting the light propagating within said LOE towards a viewer, said coupling-out arrangement being polarization-sensitive; and
(e) a non-uniformity mitigating element selected from the group consisting of: a retarder; a birefringent depolarizing element; and a partially-reflecting mixing element, said non-uniformity mitigating element being associated with said LOE and deployed to interact with the light propagating within said LOE between said coupling-in arrangement and said coupling-out arrangement to as to decrease a non-uniformity in the light redirected towards the viewer caused by said spatial non-uniformity of polarization.
2. The optical system of claim 1 , wherein said non-uniformity mitigating element comprises a retarder associated with said LOE and deployed to convert linear polarization of the light propagating within said LOE to circular polarization.
3. The optical system of claim 1 , wherein said non-uniformity mitigating element comprises a block of birefringent material having a thickness d greater than Δλ/Δn, where Δλ is the spectral bandwidth of the light and Δn=is the difference between the extraordinary and the ordinary refractive indices of the birefringent material, so as to achieve depolarization.
4. The optical system of claim 1 , wherein said non-uniformity mitigating element is a flat element deployed substantially perpendicular to said major external surfaces of said LOE.
5. The optical system of claim 1 , wherein said non-uniformity mitigating element is a flat element located at one of said major external surfaces of said LOE.
6. The optical system of claim 1 , wherein said non-uniformity mitigating element is a flat element deployed within said LOE in a plane oblique to said major external surfaces of said LOE.
7. The optical system of claim 1 , wherein said non-uniformity mitigating element is at least one partially-reflecting surface deployed within said LOE, parallel to said first and second major external surfaces.
8. The optical system of claim 7 , wherein said partially-reflecting surface is deployed in the middle of a thickness of said LOE.
9. The optical system of claim 7 , wherein said at least one partially-reflecting surface is implemented as two partially-reflecting surfaces deployed so at to subdivide a thickness of said LOE into three portions.