| High-refractive-index material offers a new design space for AR displays, making the rainbow effect a thing of the past.

When users put on AR glasses, they expect a perfect blend of virtual content and the real world, not the persistent colored fringes in their field of view. This rainbow effect, caused by the dispersion of ambient white light within the waveguide, has long plagued the industry.

Today, an innovative solution based on silicon carbide (SiC) material is bringing a breakthrough to this challenge.

01 Understanding the Physical Nature of the Rainbow Effect

In the field of AR displays, the rainbow effect is a familiar yet thorny problem. Upon close observation of any AR device using grating waveguides, it's hard to ignore the colored streaks accompanying the image with slight adjustments in viewing angle.

The physical root of this phenomenon lies in the waveguide's microstructure:

The characteristic size of optical gratings is on the same order of magnitude as the wavelength of light. When ambient white light hits these micro-nano structures, different wavelength components diffract at their own specific angles.

Much like a prism splitting white light into a spectrum of colors, the grating structure within the waveguide similarly acts as a beam splitter, separating the otherwise uniformly mixed white light into its colored components.

From the iridescence on soap bubbles to the dazzling reflections from a CD, these everyday phenomena share the same physical mechanism with the AR waveguide rainbow effect: diffraction and interference effects at the micro-nano scale.

The core of the problem is that when these physical phenomena occur in AR displays, they transform from beautiful natural occurrences into technical flaws that impair the user experience.

02 The Unique Solution Offered by Silicon Carbide

Traditional solutions often attempt to directly suppress the generation of the rainbow effect. However, silicon carbide material offers a distinctly different technical path: instead of eliminating the rainbow, it prevents it from entering the human eye.

The core of this solution lies in the material's fundamental properties: Silicon carbide possesses a significantly higher optical refractive index than traditional materials.

This characteristic enables designers to adopt grating structures with smaller periods. Smaller-period gratings produce larger diffraction angles, causing most of the "rainbow light" diffracted from ambient light to propagate at such extreme angles that it completely misses the observable range of the human eye.

It can be likened to adjusting the angle of a lamp to direct glaring light away from the observer's line of sight while maintaining good illumination of the space.

The limitations of traditional materials thus become apparent:

Conventional optical materials, if using excessively small grating periods, face a fundamental physical limitation – the diffracted light angles become too large, exceeding the transmission range supported by the waveguide, directly leading to a significant reduction in the field of view (FOV).

The high refractive index of silicon carbide precisely breaks through this bottleneck, creating feasibility for small-period grating design while maintaining a large FOV.

03 The Art of Balance in Systems Engineering

Silicon carbide material provides theoretical possibility, but transforming it into a practical product requires meticulous systems engineering.

This process reflects a universal pattern in technological development:

Early-stage technological development often pursues breakthroughs in a single metric. When physical limits are approached, the direction of innovation shifts toward system-level协同优化 – finding the optimal balance point among multidimensional parameters.

The development of silicon carbide waveguides follows this same path: the advantages in optical performance brought by the high refractive index must be weighed against processing techniques, manufacturing costs, system integration, and other dimensions.

Excellent engineering never seeks the extreme of a single metric, but rather finds the most elegant balance under all constraints. This also explains why silicon carbide waveguides are only gradually becoming practical as the relevant process chains mature.

04 Technical Implications and Future Outlook

The successful strategy of silicon carbide waveguides in addressing the rainbow effect provides an important paradigm for technological innovation: When directly solving a problem encounters a bottleneck, reconfigure the system parameters to open up a new path.

This mindset has been repeatedly validated throughout the history of technology:

• Architectural innovation breaks performance bottlenecks by redefining system structures.

• Materials science expands design boundaries by altering fundamental physical properties.

• Integration technologies enhance system performance by optimizing component relationships.

In the field of AR optics, silicon carbide waveguides demonstrate similar wisdom – not obsessing over completely eliminating the physical phenomenon itself, but rather making its impact disappear from the user experience through the synergy of material and design.

Silicon carbide is not a panacea. The design of small-period gratings also introduces new challenges: higher machining precision requirements, more complex optical design, and stricter process control.

But its true value lies in pointing the direction for innovation: on the path of AR optical development, material innovation and design innovation are of equal importance. The breakthrough for next-generation AR display technology likely lies within the systematic optimization of these fundamental materials.