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As the demand for photonic devices in Augmented Reality (AR) and Virtual Reality (VR) increases, the need for efficient, miniaturized components becomes more pressing. Two components under scrutiny are metalenses and optical combiners, which are crucial in applications ranging from automotive LIDAR and cameras to AR/VR systems. However, it is challenging to support high-volume manufacturing for these components without compromising performance.
Understanding Manufacturing-Aware Metalenses
Meta optics – also known as flat optics – are transitioning into High Volume Manufacturing (HVM) using traditional integrated circuit manufacturing techniques. Meta optics are built as a metasurface that is comprised of meta-atoms. The meta-atoms are subwavelength unit-cells built in high-refractive-index films with a thickness range of approximately 0.5 to 3+ μm. The metasurface may be used as a focusing lens, splitter, waveguide, or to serve some other optical function.
Metalenses, with their potential to revolutionize imaging systems, are gaining interest in the field of optics. However, they are challenging to design and manufacture in high volume; issues include mask manufacturing, corner rounding, etching, fillet, layout generation, and substrate flatness impact, among others. The photolithography and etch processes often fail to achieve desired results, such as square corners and perpendicular sidewalls. These deficiencies negatively impact metasurface performance metrics.
Taking a “manufacturing-aware” design approach to optimizing metalenses helps designers overcome manufacturing challenges. This approach integrates advanced technology from optical design (RSoft Photonic Device Tools) and manufacturing process design (Synopsys Proteus, S-Litho and Sentaurus Process Explorer) software, to ensure that a manufactured metalens is closer to optimal performance for a specific manufacturing technique. It aids in implementing design rules from and to optical and manufacturing design, shortening the design cycle, and striving for a first-time-right metalens design.
Figure 1. Metalens design flow incorporating manufacturing limitations. A designer’s meta-atom set is simulated in manufacturing, creating a “manufacturing-aware” meta-atom library. The meta-atom library is then used to develop a metalens with improved manufactured performance.
Addressing Similar Challenges in AR/VR Devices
Manufacturing challenges aren't unique to metalenses. Low-cost and high-precision fabrication of surface relief gratings on AR/VR waveguide combiners is one of the critical steps in realizing devices suitable for mass adoption.
Surface relief gratings (SRGs) have micrometer-scale features and are sensitive to surface fillet, etch, and roughness introduced during manufacturing. For an optical combiner, a key parameter is to carefully control the spatial diffraction efficiencies of the SRG.
Any deviation of the shape of the SRG conducts to a variation the diffraction efficiency, ignoring those variations at early stage of the optimization would generate multiple design loop to converge to the targeted performance of the optical combiner as the uniformity of light on the eyebox. Having a “manufacturing-aware” optimization flow for the optical combiner would be beneficial to the final performance and robustness of the design as the manufacturing defects of the SRG are now part of the characterization of the component.
Synopsys offers a complete design flow, as shown in Figure 2, that allows the designer to integrate the manufactured profile of SRG at early stage of the optimization. The optimization of the optical combiner is performed to satisfy the requirement for illuminance uniformity on the eye box as well as picture quality and color definition.
Figure 2: Schematic of the first-time right design approach
using the manufactured SRG profiles as the initial point.
Conclusion
Incorporating manufacturing awareness in optical design, particularly for metalenses and AR/VR devices, is beneficial for a robust and efficient optical design flow. By understanding and simulating the impact of manufacturing processes on these devices, designers can improve performance, reduce design-manufacturing-test loops, and save both time and money. As the demand for these devices continues to grow, such an approach will be crucial in advancing optics and photonics technologies.
Read the full papers at the SPIE Digital Library (subscription may be required):
- Optical and manufacturing design aware flow for metalenses
- Computational patterning and process variation impact on photonics devices
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