Patent NZ-724344-A (NZ)
Title: Apparatus for optical see-through head mounted display with mutual occlusion and opaqueness control capability
Inventor: GAO CHUNYU
IPC: G02B27/01
Filed: 2013-04-05
Abstract: Disclosed is a compact optical see-through head-mounted display system, configured to combine a see-through path with a virtual view path such that an opaqueness of a see-through view can be modulated to occlude portions of the see-through path, the system comprising: a microdisplay for generating a virtual image to be viewed by a user on the virtual view path; a spatial light modulator for modifying light from an external scene to block portions of the see-through path that are to be occluded; an objective optics configured to receive and fold the light from the external scene on the see-through path and to focus the light from the external scene as an intermediate image upon the spatial light modulator at a back focal plane distance of the objective optics, wherein the objective optics is a freeform prism formed by a plurality of reflective and refractive surfaces to image the external scene into the spatial light modulator; a beamsplitter configured to merge a virtual image and an occluded see-through image, producing a combined image of the virtual image from the microdisplay in those occluded portions of the see-through path; an eyepiece optics configured to magnify the combined image; an exit pupil configured to face the eyepiece optics, wherein the user observes the combined image through the exit pupil; and a plurality of surfaces configured to fold the virtual view path and the see-through path to the exit pupil, wherein the microdisplay and the spatial light modulator are optically conjugate, such that the spatial light modulator is disposed at a distance from the beamsplitter substantially equal to a distance of the microdisplay from the beamsplitter. Also disclosed is a method comprising: receiving external light from an external scene through an objective optics; folding the external light from the external scene through a plurality of surfaces to create a see-through path; focusing the external light as an intermediate image on a spatial light modulator located substantially at a back focal plane associated with a prescription of the objective optics; modulating the external light received from the external scene on the spatial light modulator to create a modulated see-through image of the external scene; transmitting the modulated see-through image of the external scene to a beamsplitter; rendering a virtual image by a microdisplay; transmitting the rendered image to the beamsplitter on a virtual view path, wherein the beamsplitter is at a distance from the spatial light modulator that is optically conjugate from the microdisplay; combining the rendered image with the modulated see-through image; and folding the combined rendered image and modulated see-through image through an eyepiece optics configured to magnify the combined rendered image and modulated see-through image. The unique positioning of the spatial light modulator and microdisplay as a function of the focal length of the objective optics (that is, the “optically conjugate” relationship dictates positioning and types of the microdisplay and spatial light modulator) seeks to permit compact form fitting (e.g. the microdisplay and SLM can be positioned closer to the beamsplitter to minimize aberrations) which seeks to address a problem associated with bulky head mounted devices. Furthermore, the positioning of the spatial light modulator and microdisplay as a function of the focal length of the objective optics enable microdisplays and spatial light modulator of common specification and beam divergences to be used without intermediate optics, thereby enabling simpler architectures which seeks to address a problem associated with the complexity of prior head mounted devices.