Liquid crystal active optics help make AR glasses feel natural

If you have worked in the XR glasses industry long enough, you know that optical display modules have made enormous progress in delivering brighter, sharper and wider-field images to the eye. While the display performance in AR glasses is very important, the optical stack also plays a crucial role, as it is responsible for how the virtual images work with the human visual system in the real world.

Today’s AR/VR glasses still rely on largely static optical paths, even though a key part of that path – the eye itself – is entirely dynamic. Eyes move and refocus depending on the distance to a visual target and adapt to changing brightness. Active optics can automatically adjust focus and brightness, making virtual content behave more like the eye expects and reducing the perceptual mismatch that contributes to visual fatigue and discomfort.

Several liquid crystal optics technologies can be used to improve the user comfort and experience when wearing AR glasses, making them feel more natural. These include pixelated dimmers, tunable lenses and switchable half-wave plates. The fact that there has been a significant number of patents and papers from major consumer electronics companies over the last few years related to these technologies indicates their importance for advancing AR glasses.

Pixelated, fast-switching dimming for solid virtual images

Dimming in AR serves several purposes: increasing the contrast of the virtual image against the ambient scene, blocking the real-world background where needed, and providing a true perceptual black. Most dimmers in use today are either static (like a tinted sunglass lens) or switch over seconds to minutes – far too slow to keep pace with a rendered scene.

Fast-switching liquid crystal pixelated dimming addresses this problem. By selectively dimming only the region behind a virtual object, the system can create higher contrast, support occlusion, and make a virtual image appear solid instead of washed out in bright sunlight.

Visual representation of a virtual zebra’s visibility through AR glasses under three conditions: no dimmer, global dimmer, and pixelated dimmer. Only pixelated dimming can deliver solid virtual objects in bright light without affecting the real-world view.

Tunable lenses for dynamically adjustable focus and reading glasses

Human eyes focus continuously from close range (as near as 10 cm in youth) to the far distance, adjusting optical power as attention shifts across the scene. Most AR glasses present digital content at a fixed image plane, creating a mismatch between where virtual content appears and where the eye needs to focus. This conflict – known as the vergence-accommodation conflict – is a common cause of visual discomfort in AR.

Better focal control can reduce that discomfort, improve depth realism, and allow digital content to coexist naturally with the real scene. Liquid crystal lenses achieve this by functioning as an active Fresnel lens: within a package roughly 200 microns thick on a plastic substrate, the liquid crystal is precisely oriented to create a refractive index profile that can shift the apparent image plane from near-eye distance to the horizon.

Tunable push-pull lens principle in see-through AR glasses. Combined function (equal and opposite lens power for push and pull lenses) allows the focal length of the virtual object to be changed without affecting the appearance of the real world​.

In addition to using tunable lenses for image plane adjustment, there has been interest from eyewear companies to use liquid crystal tunable lenses for providing an on/off reading glasses functionality in AI and AR glasses. This would make these glasses truly ‘all-day wearable’ for the large portion of the population who would otherwise need to switch between AR glasses and reading glasses.

Switchable half-wave plates and polarization-state control for variable dimming and dual image planes

A switchable half-wave plate (sHWP) is a liquid crystal element that toggles the handedness of circularly polarized light – converting right-handed to left-handed and vice versa – based on an applied voltage. Used between two crossed polarizers, the sHWP creates a fast-switching variable dimmer.

In this arrangement, the LC rotates the polarization of transmitted light from the first polarizer; the second polarizer then converts that rotation into an intensity modulation, allowing the lens assembly to dim from roughly 40% transmission down to 0.03%. This is the principle behind global dimmers on the market today as well as for the next-generation pixelated dimmers under development.

An sHWP can also be used to selectively direct light through different optical paths, enabling two distinct image planes from a single optical stack. Depending on the polarization state of the waveplate, the image follows either a short-focal-length path or a long-focal-length path, enabling simultaneous or gaze-selected projection at two distances.

Developing liquid crystal active optics for AI and AR glasses

Liquid crystal active optics are moving fast from a research and development state to a key requirement in next-generation AR glasses.

In addition to providing functionality, the liquid crystal optics in AR glasses need to be lightweight and fit design expectations. FlexEnable’s organic semiconductor and LC-on-plastic platform is uniquely positioned to deliver LC active optics in the form factor required – from a normal glasses form-factor to visors with complex curvatures.

FlexEnable develops liquid crystal global and pixelated dimming cells and tunable lenses on plastic, making them a small fraction of the weight and thickness of similar glass components. We have R&D capability to develop customer specific active components and work with OEMs and supply chain partners to integrate these components in their products and provide them with a route to mass production.

Contact us at info@flexenable.com for more information.