Analysis of AR Silicon Carbide Waveguides: A Design Perspective

​Material breakthroughs often elevate entire industries to new heights, even unlocking new technological frontiers for humanity. The advent of silicon revolutionized semiconductor and computing eras, laying the foundation for silicon-based life. Could silicon carbide (SiC) similarly propel AR waveguides to unprecedented heights? Let’s explore waveguide design first.

Only by understanding system-level requirements can we clarify material optimization directions. The classic AR waveguide architecture originated from Dr. Tapani Levola of Finland, exemplified by Microsoft HoloLens. These waveguides consist of three zones: entrance pupil, expansion pupil, and exit pupil. Finns have been pivotal in AR waveguide development, from Nokia to HoloLens and later companies like Dispelix.

**Waveguide Design Basics:**​

1. ​**Entrance Pupil Zone:**​ Incoming light from the optical engine is coupled into the base (glass, SiC, or resin) via gratings. Functioning similarly to fiber optics, light undergoes total internal reflection (TIR) when incident angles meet critical thresholds, confining it within the base for transmission to the expansion pupil.
2. ​**Expansion Pupil Zone:**​ Light is replicated horizontally (X-axis) and propagated toward the exit pupil.
3. ​**Exit Pupil Zone:**​ Light is further replicated vertically (Y-axis), ultimately exiting the waveguide to the human eye. If the optical engine’s exit pupil (waveguide entrance) resembles a "disc," the AR waveguide’s purpose is to replicate this "disc" into multiple copies (e.g., 4x4) at the exit pupil. Ideally, these replicas overlap seamlessly to form a uniform, high-brightness light field with consistent color and brightness across the entire surface, ensuring visual uniformity regardless of gaze position.

**Key Design Considerations for AR Waveguides:**​

• ​**FOV (Field of View):**​ Determines the screen size perceived by users and influences optical engine design.
• ​**Eyebox:**​ Ensures complete image visibility within user head movement ranges, affecting comfort.
• ​**Additional Metrics:**​ Including brightness/color uniformity, MTF (modulation transfer function), and system integration.

The AR waveguide design process typically involves:

1. Defining FOV and eyebox requirements.
2. Selecting a waveguide architecture.
3. Establishing optimization variables/objectives.
4. Iterative refinement through simulation and testing.

Why Silicon Carbide Matters:​
Critical to waveguide performance is the ​k-vector wavevector diagram, which maps light propagation modes based on wavelength and angle. The central square represents the FOV of the incident light, while the annulus indicates the maximum FOV supported by the waveguide material’s refractive index. Materials with higher refractive indices (e.g., SiC) expand the outer boundary, enabling broader FOVs.

Each grating superimposes an additional wavevector onto incoming light, shifting its position within the annulus depending on wavelength. Thus, single-chip RGB implementations face reduced FOV compared to monochromatic systems due to dispersion.

**Alternatives to High-Refractive-Index Materials:**​

1. ​**FOV Stitching:**​ Architectures like Hololens’ Butterfly split the FOV into halves via lateral gratings, later recombining them at the exit pupil. This approach enables large FOVs even with low-index materials (e.g., glass with ~1.8 refractive index). Hololens 2 achieved over 50° FOV using this method.
2. ​**2D Grating Designs:**​ Further expand FOV potential through advanced patterning.

**SiC Advantages:**​
While high-refractive-index glass (e.g., 1.8) currently supports 50° FOVs without difficulty, SiC offers superior scalability for FOVs exceeding 60°. Designers favor SiC for its flexibility, but end-users prioritize performance, cost, portability, and maturity. Material selection ultimately depends on product teams balancing application needs, pricing, specifications, and supply chain readiness.

**Key Takeaways:**​

1. High-refractive-index glass suffices for 50°+ FOVs in mainstream applications.
2. SiC becomes essential for achieving 60°+ FOVs.

Materials are choices at the component level, serving system functions and ultimately users through products. Decision-making requires holistic consideration of scenarios, form factors, architectures, components, and materials.

ZMSH is well-equipped to provide high-quality silicon carbide (SiC) wafers that meet the advanced requirements of AR glasses technology. With exceptional thermal conductivity, optical clarity, and mechanical strength, ZMSH's SiC wafers are ideal for use in AR waveguides, enabling ultra-thin, lightweight lenses with superior heat dissipation and full-color display capabilities. By integrating ZMSH's SiC wafers, AR devices can achieve enhanced performance, delivering larger display areas and improved user comfort. Our SiC wafers are manufactured to meet the highest industry standards, making ZMSH a reliable partner for cutting-edge AR applications.

SiC Wafer - Prime Dummy Reaserch Grade For Semiconductor