Google Invents Smartglasses with a Curved Thin See-Through Lightguide with Large Eyebox that includes a Half-Wave Plate
Last week the U.S. Patent and Trademark Office officially published a patent application from Google that relates to possible future smartglasses focused on curved thin see-through lightguide with large eyebox. The curved light-guide includes a half-wave plate (HWP) to flip an input polarization for a main image to an orthogonal polarization and a dielectric mirror to act as a weak analyzer to dim side images.
Google notes in their patent background that conventional eyewear display designs include a microdisplay (“display”) positioned in a temple or rim region of a head wearable frame like a conventional pair of eyeglasses. The display generates images, such as computer-generated images (CGI), that are conveyed into the FOV of the user by optical elements such as curved lightguides deployed in the lens of the head wearable display frame. The wearable electronic eyewear display device can therefore serve as a hardware platform for implementing augmented reality (AR) or mixed reality (MR). Different modes of augmented reality include optical see-through augmented reality, video see-through augmented reality, or opaque (VR) modes.
Light transmitted from a microdisplay to a user's eye in an eyewear display device generally undergoes multiple reflections, refractions, diffractions, and/or changes in polarization that can result in stray light within the system. Stray light within an eyewear display device reduces image contrast and can create haziness and ghost images in the field of view.
Minimizing stray light in eyewear display devices provides a user with a more enjoyable viewing experience while also reducing eye fatigue.
Curved Thin See-Through Lightguide with Large Eyebox
Google's patent application covers and describes embodiments of an eyewear display having an expanded eyebox and techniques for mitigating artifacts.
In one example embodiment, a device includes a microdisplay, a curved lightguide configured to receive display light from the microdisplay and to transmit the display light from a proximal end of the curved lightguide to a distal end of the curved lightguide, an incoupler configured to direct light from the microdisplay into the curved lightguide, wherein the incoupler is thicker than the curved lightguide, and an outcoupler disposed at the distal end of the curved lightguide, the outcoupler configured to direct a portion of the display light out of the curved lightguide toward a user's eye, wherein the outcoupled is disposed at an angle with respect to the curved lightguide to receive two interactions of the display light at a world-side of the outcoupler.
In some embodiments, the device includes a frame to carry a lens, wherein at least a portion of the curved lightguide and a first portion of the incoupler are disposed within the lens and a second portion of the incoupler is disposed within the frame.
In some embodiments, the first portion of the incoupler has a spherical eye-side surface and the second portion of the incoupler has a non-spherical eye-side surface.
Some embodiments relate to techniques for dimming side images in a curved lightguide by utilizing a polarized light source combined with a half-wave plate (HWP). Light rays traveling through the lightguide to generate a main image undergo an even number of interactions (bounces) within the lightguide, whereas light rays traveling through the lightguide to generate side images undergo an odd number of bounces within the lightguide. The HWP flips the input polarization for the main image to the orthogonal polarization and preserves the linear polarization for the side images due to the even number of bounces of main image light and the odd number of bounces of side image light. In some embodiments, the HWP is a curved HWP placed on the eye-side or the world-side of the lightguide. Once the polarization of the main image has been flipped, the display light is directed to a dielectric mirror, which acts as a weak analyzer to dim the side images by an order of magnitude. The main image polarization is aligned to s- for higher luminance and p- for the side images to dim them.
Google's patent FIG. 1 below is a block diagram of a display system including an incoupler and outcoupler configured to produce an enlarged eyebox; FIG. 2 is a diagram illustrating a curved lightguide including an incoupler thicker than the curved lightguide and an outcoupler angled to receive two bounces of display light; FIG. 4 is a diagram illustrating an eyebox in relation to a lens of a display system.
Google's patent FIG. 7 above is a diagram illustrating a display system with a gap in a low-index coating to mitigate artifacts.
For full details, review Googe's patent application 20240427150 that was published on December 26, 2024 in the U.S.