What Is Augmented Reality Optics?

To enable augmented reality (AR), an optical system projects digital images onto a transparent display positioned in front of the user's eyes, overlaying virtual information onto the real environment. You can achieve this through different types of displays, such as head-mounted displays (HMDs), handheld devices like tablets, or mounted displays like windshields.

AR headsets and mounted displays

A typical AR optical system consists of three main components:

• Light sources: Microdisplays such as organic light emitting diodes (OLEDs) or liquid crystal displays (LCDs) generate the augmented images. Binocular HMDs use two displays, one for each eye, to create a 3D effect through stereoscopy. Holographic HMDs use spatial light modulators (SLMs) to produce modulated coherent light for advanced image projection.
• Receivers: The user's eyes receive both the real-world and augmented images.
• Optical elements: Lenses and combiners blend light from the microdisplays with light from the real environment and project the combined image to the user's eyes. In AR glasses, for example, a microdisplay image passes through a series of optical components, including beam-shaping lenses, prisms, and prescription lenses, before being merged with the real scene for the viewer.

Figure 1. Prescription AR schematic diagram:

(a) Side view showing the AR beam path. The prescription lens works for vision-correction and wave-guide of the AR image. A beam shaping lens refracts light rays from a micro display that enter the prescription lens through an in-coupling prism and create a magnified virtual image at a set distance from the lens.

(b) Geometric parameters in the Prescription AR system.

(c) The 3D diagram of optical components.

Reprinted with permission. © The Optical Society.

Optical aberrations can affect image quality in AR HMDs, similar to other optical systems. Aberrations such as chromatic aberration, spherical aberration, coma, astigmatism, field curvature, and distortion can cause blur or warping in the projected images. Careful design and optimization are essential to minimize these aberrations and improve visual clarity.

Designing AR optics requires a combination of specialized software tools and expertise from multiple engineering disciplines. Optical engineers use software to create and optimize imaging systems, analyze stray light, and design diffractive optical elements. Mechanical engineers need CAD tools to lay out the system and perform thermal and structural analysis. Electrical engineers may also be involved to implement eye-tracking and manage signals sent to the optical system.

The Workflow

Optical Systems:

• You can use CODE V optical design software to trace rays through the optical system, optimize the system to reduce aberration, decrease distortion, and increase resolution as shown in a head-mounted display. You can also use augmented reality optics for automotive head-up displays (HUDs), modeled in CODE V (see next section). Then export the geometry to LightTools.
• LightTools illumination design software can model illumination, stray light and ghost images. You can also use LightTools to optimize illumination uniformity.

Design gratings using photonic design software:

Diffractive gratings couple light into the waveguide plate and couple the light out of the plate into the eyes. Gratings must be designed properly so that the optical system produces good images. For the design and optimization of gratings, you can optimize gratings based on things like diffraction angle and efficiencies of any order or combination of orders.

• RSoft DiffractMOD RCWA is a very efficient tool to rigorously calculate diffraction properties of transversely periodic devices.
• RSoft FullWAVE FDTD is another powerful tool to rigorously calculate diffraction properties of transversely periodic devices when necessary.
• RSoft MOST optimization in the RSoft CAD Environment provides a convenient method to optimize gratings with either RSoft FullWAVE or RSoft DiffractMOD.

Once you build the gratings, you can export the Bidirectional Scattering Distribution Function (BSDF) information and layout files directly to LightTools to define a surface property. All diffractive properties are included in the RSoft BSDF files, which contain information about how a surface such as thin film or patterns scatters light.

A head-up display (HUD) augments a driver’s field of view with an image from a display. You need software to model the rays traveling through the windshield and to evaluate the quality of the projected image.

CODE V has powerful application features in the HUD design space for tackling a wide range of opto-mechanical systems design challenges. Engineers can use this optical design software for CAD visualization and ray tracing. CODE V supports new freeform surfaces, providing greater design freedom for compact windshield-combiner systems. These surfaces improve aberration control as display resolution increases at the viewer’s eye (higher density display pixels) form factors shrink.

After design completion, it is important to check the final system performance against nominal criteria and for actual system as-built performance. For this, LightTools is the logical next step for viewer simulation. A reverse ray trace from spectral color objects representing a display image in LightTools shows the projected HUD image for a viewer (onto a model scene). A LightTools simulation can also help uncover unforeseen issues with stray images or reflections in the system. Also, engineers can use LightTools CAD import and measurement tools to determine:

• Eyebox to windshield distance
• Approximate angle of incidence on windshield
• Windshield to dashboard distance

LightTools simulation of real world optical system performance is an excellent asset for Keysight design engineering product users in their work.

The main difference between augmented reality (AR) and virtual reality (VR) optics is how they interact with the real environment. VR optics simulate the entire visual environment, immersing users in a completely virtual world. In contrast, AR optics capture the real environment and overlay digital information onto it, blending simulated and real elements through a visual display.

In AR, the display is typically see-through, allowing users to view both the real world and digital enhancements simultaneously. VR displays, on the other hand, only present the simulated environment, blocking out the real world.

Key differences between AR and VR optics include:

• Display requirements: AR needs high luminance displays to ensure visibility in bright environments like outdoors or operating rooms.
• Optical precision: For see-through AR head-mounted displays (HMDs), angular registration error—the difference in angle between real and virtual imagery—should be kept below 1 to 3 arcminutes for optimal clarity.
• Design considerations: AR HMDs often use a folded optical design to achieve a wide field of view (FOV) while maintaining a compact form factor. These devices must integrate an optical combiner that merges reflected light from virtual scenes with transmitted light from the real world. Designers commonly use beam splitters for prototyping, while holographic optical elements (HOEs) offer a thinner, flatter solution for specific wavelengths.

These examples illustrate how augmented reality optics are transforming a wide range of industries by enhancing situational awareness, improving decision-making, and creating more interactive experiences.

• Head-up displays (HUDs) for driving: Provides real-time information on the windshield to assist drivers.
• Surgical assistance: Superimposes procedural instructions and helpful data during medical operations.
• Combat aid: Offers enhanced situational awareness and targeting information for military personnel.