Silicon carbide

Silicon carbide (SiC) is a hard crystalline compound of silicon and carbon. It is best known as an abrasive and as a wide-bandgap semiconductor for power electronics, but it is also transparent across the visible spectrum and has a high refractive index of roughly 2.5 to 2.7. Those optical properties have made it a substrate material for the waveguide displays used in augmented reality (AR) glasses.

Meta used silicon carbide waveguides in its Orion AR glasses prototype, shown in September 2024, which Meta describes as having an approximately 70 degree field of view. According to Meta, the material's high index lets a single waveguide plate carry a field of view that would otherwise need a stack of glass plates, and it also reduces the rainbow artifacts that ambient light produces in diffractive waveguides. As of October 2026, SiC waveguides have been shown by Meta, by several Chinese optics companies and in academic papers, but the material remains expensive and difficult to process.

Reviewed 21 October 2026. Checked every claim against the cited Meta pages, Road to VR, UploadVR, TrendForce, Goertek, Magic Leap and KGOnTech pages, the Acheson profile and patent, and Crossref/arXiv/full-text records of the cited papers. About review dates.

Material properties

Silicon carbide occurs in many crystal forms, called polytypes. A 2022 review in Applied Physics Reviews by Ailun Yi and colleagues counts about 250 polytypes, of which only three (cubic 3C, and hexagonal 4H and 6H) can be grown stably and are commercially available for optoelectronic devices. The review notes that the properties of the polytypes differ slightly. It gives the following ranges for SiC:

Property	Value given for SiC
Bandgap	2.3 to 3.2 eV
Transparent window	0.37 to 5.6 µm
Refractive index	2.5 to 2.7
Thermal conductivity	3.6 to 4.9 W cm-1 K-1
Mohs hardness	9.2 to 9.5

Source: Yi et al. (2022), Table 1.

For comparison, the same table lists a thermal conductivity of 0.042 W cm^-1 K^-1 and a refractive index of 2.2 for lithium niobate. The hexagonal polytypes are optically anisotropic. In 1971 P. T. B. Shaffer of the Carborundum Company measured the refractive index of the four common SiC polytypes over the visible range and found that birefringence generally increases with the hexagonal character of the polytype.

History

Edward G. Acheson produced silicon carbide in 1891 while trying to use electric heat to impregnate clay with carbon. He found that the shiny crystalline product was useful as an abrasive, named it carborundum, and in 1894 set up the Carborundum Company in Monongahela City, Pennsylvania, to make abrasive products such as grinding wheels. His US patent 492,767, filed on 10 May 1892 and granted on 28 February 1893, claims the crystalline compound of silicon and carbon and its production by passing an electric current through materials containing carbon and silica.

According to Meta, the main application of SiC is high-power electronics, such as those in electric vehicles. Integrated photonics research has also used SiC for chip-scale waveguides, nonlinear optics and quantum information applications.

Use in AR waveguides

Why a high index matters

In a waveguide combiner, light from a microdisplay projector is coupled into a thin transparent plate, travels along it by total internal reflection, and is coupled out toward the eye. Diffractive designs use surface gratings for the in-coupling, pupil expansion and out-coupling. The range of angles that a plate can guide grows with the refractive index of its material. Meta's AR waveguides technical lead Giuseppe Calafiore said that "the larger the refractive index of a material, the larger field of view the display can support."

Meta's blog lists three candidate materials and their indices: glass at 1.8 (the highest-index glass the team had when Calafiore joined Oculus Research in 2016), lithium niobate at about 2.3, and silicon carbide at 2.7. Meta calls 2.7 the highest refractive index known for an optical application, a 17.4 percent increase over lithium niobate and 50 percent over glass. Other researchers use slightly lower values for the substrates they tested; a 2026 Science Advances paper used n = 2.6 for its SiC waveguides.

Rainbow artifacts

Diffractive waveguides can show "rainbows", colored streaks created when ambient light from the outside world is diffracted by the gratings toward the eye. Meta describes rainbows as colorful streaks of light created when ambient light reflects off the waveguide. In their 2024 preprint, Boqu Chen and colleagues at Zhejiang University, Westlake University and Moldnano explained why a SiC waveguide can avoid this: its gratings can use a smaller period, so ambient light is diffracted at larger angles, mostly outside the range the eye box receives. For comparison they calculated that a waveguide with n = 1.9 needs a 370 nm grating period for a single-plate full-color design with a 30 degree field of view, and that some blue and green ambient light diffracted by such a grating would reach the eye; their SiC design used a 262 nm period. Meta's Barry Silverstein, director of research science at Reality Labs, said that one of SiC's properties "is that it gets rid of those rainbows".

Heat and weight

Calafiore pointed out that SiC conducts heat, whereas plastic, glass and lithium niobate are poor thermal conductors. Display analyst Karl Guttag wrote in 2026 that SiC is roughly 200 to 400 times more thermally conductive than glass and almost as scratch resistant as diamond, but brittle, so broken pieces have sharp edges and need to be laminated or contained for eye safety.

Meta Orion

Reality Labs research manager Nihar Mohanty said that in 2019 he and his then manager Matt Colburn set up Meta's own fabrication facility because no one could produce etched SiC waveguides. In 2019 the team and its suppliers also found that silicon carbide in its purest form is very transparent, and Calafiore said that the production process could be changed to optimize the material for optical rather than electronic properties. With the 1.8 index glass then available, reaching the desired field of view required stacking multiple waveguide plates, and Calafiore said that three pieces of glass per lens were too heavy and too thick for a pair of glasses. In July 2020 the team decided that SiC was the best choice for three reasons: it needed only a single plate with smaller mounts, it had better optical properties, and it was lighter than a dual-plate glass design.

Orion's gratings are slant etched, with grating lines sloped diagonally rather than vertical. Mohanty said Meta was the first to slant etch directly on the devices, and that nanoimprinting, which the industry had relied on, does not work for substrates with such a high refractive index. Meta's Orion product page describes "optical-grade silicon carbide (SiC) lenses" and an optical stack that minimizes stray light effects such as rainbows. Its separate silicon carbide page says that production complexity remains high for the industry because the material is relatively new.

Meta has not sold Orion; its product page describes it as an internal product that is not available to the public. UploadVR reported in March 2025 that Meta's planned follow-on AR glasses, codenamed Artemis, were glass-based and would not have Orion's field of view. The same report cited Meta as saying that suppliers on three continents were "heavily pursuing" optical-grade SiC, and quoted Silverstein: "Orion proved that silicon carbide is a viable option for AR glasses".

Cost

SiC has historically been expensive, and it is one of the hardest known materials, so working it requires diamond tooling. Meta said in 2025 that overcapacity built for electric vehicles had begun to lower substrate costs, and that suppliers were moving from 4-inch to 8-inch wafers, with some developing precursors to 12-inch wafers. Road to VR noted that wafers made for electric vehicles are not optical grade, so surplus electronics wafers cannot simply be reused for lenses. In December 2025 TrendForce reported that Shenzhen Kuotan Semiconductor Technology planned a RMB 1.15 billion production base for 12-inch optical-grade SiC in Huizhou, Guangdong, aimed in part at AR and AI glasses waveguides, with a first-phase target of 50,000 wafers a year.

Other developments

Group	Date	SiC waveguide work
Westlake University and Moldnano	August 2025	Paper in eLight: a single-layer, full-color SiC diffractive waveguide made on 4-inch SiC wafers with a "NIL-to-lift-off" process, in which nanoimprint lithography creates a metal mask for transferring the grating pattern into the SiC; packaged single lens 3.795 g and 0.75 mm thick, with a 0.2 mm Fresnel lens for vision correction
Zhejiang University and LLVision	September 2025	Paper in Photonics: single-layer full-color SiC diffractive waveguide glasses with a 55 degree field of view, 2.12 g per lens and rainbow suppression, using a "Period-Limited" design method
Goeroptics (announced by Goertek)	February 2026	F50Se full-color SiC waveguide module shown at SPIE AR, VR, MR 2026, with a 50 degree field of view, a full-color LCoS microdisplay and, by the company's figure, over 1,500 nits in the eye box; also an F30Se etched SiC module 0.65 mm thick
Magic Leap	Undated web page (accessed October 2026)	Lists silicon carbide, with high-index glass and polymers, among the materials it chooses for waveguides
Zhejiang University and LLVision	August 2026	Paper in Science Advances: metagrating couplers designed with a physics-constrained generative network; the SiC (n = 2.6) device reached a 75 degree field of view, 1,100 nits and 49.7 percent luminance uniformity
Westlake University and Moldnano	September 2026	Preprint describing a 0.35 mm, 1.98 g SiC diffractive waveguide with gratings whose depth and duty cycle vary across the plate, and a nanoimprint-compatible method for patterning four lens pairs per 8-inch wafer; full-color performance over a 30 degree field of view reported from simulation

Glass remains a competing route to wide fields of view. At CES 2026 Lumus, which developed the waveguide used in the Meta Ray-Ban Display, said its ZOE glass waveguide was the first geometric waveguide to surpass a 70 degree field of view, the figure Meta had reached with SiC in Orion.

Limitations

In a September 2026 analysis of five SiC waveguides, including Orion's and those of Moldnano and LLVision, Guttag judged the color uniformity of all of them to be poor. He wrote that the material's dispersion and birefringence make diffractive design difficult, that the high index makes surface reflections and ghost images harder to control with anti-reflection coatings, and that SiC waveguides will be inherently more expensive than glass ones because of small wafers, crystal defects and difficult polishing and etching. Anisotropy is also a research topic: a 2026 SPIE paper by Jonathan Heinz-Garcia and Russell Chipman addressed the impacts of SiC substrate anisotropy on waveguide design. Meta has said that work on bringing down cost is ongoing.

See also

• Waveguide display
• Diffractive waveguide
• Refractive index
• Meta Orion
• Optical combiner
• Nanoimprint lithography
• AR glasses