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 illumination corresponding to a collimated image from an aperture, the illumination 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 prism attached to said first major external surface of said LOE, said coupling prism providing at least part of an image injection surface angled obliquely to said major external surfaces, said projector being associated with said image injection surface and oriented such that the chief ray and the angular field about the chief ray are injected through said image injection surface at angles of incidence relative to said major external surfaces greater than a critical angle for internal reflection at said major external surfaces; and
(d) a reflective polarizing beam splitter deployed at an interface between said major external surface and said coupling prism parallel to said major external surfaces, at least part of the illumination being incident on said beam splitter with a first polarization and being transmitted by said beam splitter from said coupling prism into said LOE, light corresponding to a conjugate image of the collimated image and having a second polarization incident on said beam splitter from within said LOE being reflected from said beam splitter so as to propagate within said LOE by internal reflection.
2. The optical system of claim 1 , further comprising a waveplate deployed in a path of at least a part of the illumination to convert the illumination between said first polarization and said second polarization.
3. The optical system of claim 2 , wherein said waveplate is a quarter-wave plate associated with at least part of said second major external surface of said LOE.
4. The optical system of claim 2 , wherein said waveplate is a half-wave plate deployed in overlapping relation to a first part of said aperture without overlapping a second part of said aperture.
5. The optical system of claim 4 , wherein said first part of said aperture projects illumination through a part of said image injection surface from which light passes into said LOE without traversing said beam splitter.
6. The optical system of claim 4 , wherein said projector is configured to project illumination of said second polarization, wherein said first part of said aperture projects illumination through a part of said image injection surface from which light passes through said beam splitter, said half-wave plate converting illumination of said second polarization into illumination of said first polarization.
7. The optical system of claim 1 , wherein said image injection surface is provided in part by said coupling prism and in part by a surface of said LOE.
8. The optical system of claim 1 , wherein said image injection surface is provided entirely by said coupling prism.