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Magic Leap One Lightwear AR glasses, an example of AR headphones
Apple has been working on a set of portable augmented reality peripherals for some time. A constant question about any future “Apple Glasses” peripherals has been about how Apple can maintain its preference for sleek, high-performance systems rather than most of some current headsets. A new patent provides part of the answer.
“Scatter Compensation Optical System” is a patent application that describes a method that combines a small “holographic optical element” that can be projected onto a reflective surface. Therefore, the holographic projector could be on the edge of the Apple Glasses, and the total or semi-reflective surface could be the lenses in front of the user’s eyes.
“Head-mounted displays generally include close-to-eye optics to create ‘virtual’ images,” says the patent. “In the past, HMDs have faced a variety of technical limitations that have reduced image quality and increased weight and size. Also, conventional mirrors and grille structures have inherent limitations.”
The patent says that the angle of reflection between the optical element and the conventional mirror has a “suboptimal” impact on performance. This worsens if there are many different projectors with “multiple reflective axes that would cope unacceptably with angle of incidence and / or wavelength”.
Apple’s answer is to use a type of reflective surface called an “oblique mirror.” This is a material that while reflecting light, can only reflect certain frequencies or colors, and reflects everything at a different angle. The glasses could use different oblique mirrors to route the colors of different projectors and make them all go to the wearer’s eyes.
The advantage of a smaller system is clear, but if it didn’t have problems, everyone would be doing it. This projection and reflection is known as scattering, and scattering has problems.
“Dispersion can cause chromatic aberrations in optical devices,” says the patent. “These chromatic aberrations can have a degrading effect on an image from a reflective optical device.”
What the user could see without a system like Apple’s is perhaps similar to when the binocular lenses are not fully aligned and the edges of the image are blurred or have a rainbow-like color effect. Unlike binoculars, these types of augmented reality images can also appear absent-mindedly low-resolution.
Patent detail showing how an optical element can be reflected in the user’s eyes
The lenses in a device like Apple Glasses must allow the user to see the real world and display computer generated images. What Apple proposes is that the material can also reflect multiple images in the user’s eyes, without the user noticing that the image was created from more than one source.
Apple proposes that the optical element that projects these images be holographic. Much of this patent relates to how one or more holographic projections can be recorded.
“Holographic optical elements can be used in head-mounted devices or other systems and can be built from a recording medium,” he says. “The recording medium can sometimes be referred to here as a grid medium. The grid medium can be arranged between waveguide substrates. An input coupler like a prism can couple the light into the waveguide.”
Having the ability to reproduce or retransmit holographically recorded images, Apple’s proposal describes a system in which Apple Glasses’ lenses “have reflective axis angles that vary by less than 1.0 degrees.”
The invention is credited to five inventors, Jonathan B. Pfeiffer, Adam C. Urness, Frieze Schlottau, Mark R. Ayres and Vikrant Bhakta. Among them, they have dozens of related prior patents, including Bhakta’s “Field Division Element Projection Device” and Ayres’ “Holographic Multiplexing Process”.
This patent follows previous ones that are also related to the optimization of images to show in AR glasses.
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