Patent NZ-740631-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 one aspect there is provided a compact optical see-through head-mounted display, capable of combining a see- through path with a virtual view path such that the opaqueness of the see-through path can be modulated and the virtual view occludes parts of the see-through view and vice versa, the display comprising: a microdisplay for generating an image to be viewed by a user, the microdisplay having a virtual view path associated therewith; a reflection-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 two-reflection freeform prism comprising four optical freeform surfaces: refractive surface S4, reflective surface S5, S4’ and refractive surface S6; a first beamsplitter configured to reflect the see-through path onto a mirror; a relay lens configured to generate another intermediate image upon the spatial light modulator; a second beam splitter configured to merge a 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; 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; and a mirror to fold the see-through path. The objective optics is disposed upon the front layer of the display, where the first beam splitter is disposed upon the front layer of the display. The mirror is disposed upon the front layer of the display at the focal plane of the objective optics, facing the spatial light modulator. The spatial light modulator is disposed on the back layer of the display, facing the second beam splitter. The relay is disposed between the first and the second beam splitters. The microdisplay is disposed on the back layer of the display, facing the second beam splitter. The second beam splitter is disposed on the back layer such that the direction of light transmission from second the beam splitter is facing the eyepiece. The eyepiece is disposed upon the back layer of the display. The incoming light from the external scene enters the objective optics through the refractive surface S4, consecutively reflects upon the reflective surfaces S5, S4’, and exits objective optics through the refractive surface S6. The incoming light is reflected by the first beam splitter onto the mirror, where it forms an intermediate image. The mirror reflects the light from the front layer onto the relay lens, whereupon the relay lens forms another intermediate image upon the spatial light modulator. The spatial light modulator modulates the light in the see-through path to remove the light to be occluded. The spatial light modulator reflects the modulated light into the second beam splitter, whereupon the light from the microdisplay enters the second beam splitter. The second 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 cumbersome helmet-like form factor of the prior art which prevents the acceptance of such technology. Advantageously, inside the objective optics an intermediate image 460 is formed to erect the see-through view which eliminates the necessity of using an erection roof reflective surface which can lead to a more compact design by folding the optical path inside the objective prism multiple times.