Patent NZ-725339-A (NZ)
Title: Occluding in freeform optical relay system with beamsplitters
Inventor: GAO CHUNYU
IPC: G02B27/01
Filed: 2013-04-05
Abstract: The present invention relates to the field of head mounted displays. In an aspect there is provided a compact optical see-through head-mounted display comprising: a microdisplay for generating an image to be viewed by a user, the microdisplay having a virtual view path associated therewith; a transmission-type spatial light modulator for modifying the light from an external scene to block portions of the see-through view that are to be occluded, the spatial light modulator having a see-through path associated therewith; an objective optics, facing an external scene, configured to receive the incoming light from the external scene and to focus the light upon the spatial light modulator, where the objective optics is a three-reflection freeform prism, comprising five optical freeform surfaces: refractive surface S4, reflective surface S5, S4’ and S6 and refractive surface S7, where the objective optics is configured to form an intermediate image inside the objective optics; a beamsplitter configured to merge a digitally generated virtual image from a microdisplay and a modulated see-through image of an external scene passing from a spatial light modulator, producing a combined image; an eyepiece configured to magnify the combined image, where the eyepiece is a two-reflection freeform prism, comprising four optical freeform surfaces: refractive surface S1, reflective surface S2, reflective surface S1’ and refractive surface S3; and an exit pupil configured to face the eyepiece, the exit pupil whereupon the user observes the combined view of the virtual and see-through views in which the virtual view occludes portions of the see-through view. The objective optics is disposed upon a front layer of the display. The spatial light modulator is disposed on the back layer of the display at or near an intermediate image plane of the see-through path, facing a side of the beam splitter. The microdisplay is disposed on the back layer of the display, facing a different side of the beam splitter. The beam splitter is disposed such that the see-through path is merged with the virtual view path and the light from the merged path is directed to the eyepiece. The eyepiece is disposed upon the back layer of the display. Incoming light from the external scene enters the objective optics through the refractive surface S4, is consecutively reflected by the reflective surfaces S5, S4’ and S6, and exits the objective optics through the refractive surface S7. The incoming light forms an intermediate image at its focal plane on the spatial light modulator, whereupon the spatial light modulator modulates the light in the see-through path to occlude portions of the see-through view. The spatial light modulator transmits the modulated light into the beam splitter. The light from the microdisplay enters the beam splitter. The beamsplitter merges the modulated light in the see-through path with the light in the virtual view path and folds toward the eyepiece for viewing. The light from the beam splitter enters the eyepiece through the refractive surface S3, then is consecutively reflected by the reflective surfaces S1’ and S2, and exits the eyepiece through the refractive surface S1 and reaches the exit pupil, where the viewer’s eye is aligned to see a combined view of a virtual view and a modulated see-through view. This aspect addresses a problem associated with simplifying simplifying the optical design of the display. Advantageously, using an identical structure for the eyepiece and objective is that the optical design strategy of one prism can be readily applied to the other, which helps simplify the optical design, correct odd order aberrations, such as coma, distortion and lateral colour.