Waveguides are the optics used in smart glasses to deliver a virtual image to the eye from a projector, which is usually situated in the frame. Waveguides fit within the eyepiece, which is transparent to allow light from the real world to reach the eye. This article assesses various strengths and weaknesses of different reflective and diffractive waveguide technologies. Metrics assessed include field of view (FoV) enabled, cost, weight, thickness, optical efficiency, transparency and image quality.
IDTechEx's report, "Optics for Virtual, Augmented and Mixed Reality 2026-2036: Technologies, Forecasts, Markets", provides insight into the optics required for augmented reality (AR) and virtual reality (VR) devices. Technologies are assessed via bespoke technology benchmarking, and the expected market outlook is illustrated by market forecasts from 2026 to 2036.
Whilst this article aims to highlight some of the strengths and weaknesses of waveguide technologies used for AR optics, it is important to note that many metrics used to benchmark waveguide technologies are intertwined. For example, by increasing the FoV of a waveguide, there can be knock-on effects to form factor, optical efficiency, and image quality. Furthermore, there is a synergy between the development of AR optics and displays. Therefore, in many cases, the light engine, or device as a whole, must be evaluated in comparison to others.
Reflective waveguides
Reflective waveguides are one of the most compelling technologies for AR, and are the optics used in Meta's Ray-Ban Display smart glasses. These optics are supplied by Lumus, regarded by many as extremely high quality. As reflections are inherently wavelength independent, unlike diffraction, there are no issues with color accuracy for reflective waveguides. Furthermore, the optical efficiency of the waveguide is almost an order of magnitude higher than other designs. Reflective waveguides can be made from polymer or glass substrates.
A key disadvantage of reflective waveguides is the manufacturing cost, especially for glass waveguides. Glass reflective waveguides are made from dozens of parts, each requiring traditional manufacturing processes such as gluing and polishing. This can result in challenges with yield. However, polymer reflective waveguides may avoid many of these challenges, for example, Optinvent's waveguide produced via injection molding.
SRG waveguides
Surface relief grating (SRG) waveguides are a type of diffractive waveguide which are also very compelling. SRG waveguides, such as those developed by Magic Leap, are capable of enabling a wide FoV of 70° whilst also enabling a thin eyepiece and compact form factor. This is vital for developing fashionable smart glasses. However, SRG waveguides tend to struggle compared to reflective waveguides in terms of optical efficiency, which can make factors such as battery life challenging.
There have been several innovations into manufacturing techniques and materials for the diffractive grating structures on the surface of the waveguide. Variations in aspect ratio and slant angle may be able to improve several of these challenges with optical efficiency. Furthermore, atomic layer deposition of high refractive index materials onto the grating structures can also aid further technological improvements.
Holographic waveguides
Holographic waveguides are another type of diffractive waveguide and operate in a similar way to SRG waveguides. The diffractive structures are produced by holographic exposure and phase separation of a liquid crystal photopolymer matrix which is sandwiched between two glass substrates. This technology is not as widespread but has been successfully developed by DigiLens and used in its enterprise device, the DigiLens Argo. Holographic waveguides tend to be thicker but can also be used for high image quality and transparency.
Substrate materials
Most waveguide players are now developing products utilizing both polymer and glass substrates. Whilst glass is associated with higher image quality, a shift to polymer substrates can reduce material costs, weight, and improve durability. Polymers are lower refractive index than glass, and therefore for the same thickness product may have reduced FoV. Many players within the industry believe that in the long-term polymer waveguides will dominate.
A substrate material for the future is silicon carbide, which was utilized in Meta's Orion prototype shown in 2024. Applied Materials have also noted that advanced materials such as silicon carbide and lithium niobate are of interest. These materials would target the high-end of the market. The material is higher refractive index than glass which could help shrink the size and weight of the waveguide. The main issue with silicon carbide as a waveguide material is the associated material availability and costs.
For further detail of AR optics, as well as optics for VR, see IDTechEx's report, "Optics for Virtual, Augmented and Mixed Reality 2026-2036: Technologies, Forecasts, Markets". An introduction to each technology, the company landscape and a SWOT analysis are provided for each technology. An assessment of the extended reality (XR) market and the applications of XR technology is also included.
