We developed, tested, and applied a software tool that automatically generates high-accuracy CAD models of freeform elements with datums and fiducials, facilitating the efficient transition from freeform design to fabrication and measurement.
The geometry of a waveguide NED sets a fundamental limit on the in-coupling efficiency. We designed a metagrating with 28% minimum field efficiency surpassing the SRG's 20% efficiency and nearly matches the limit of 29%.
Waveguide displays are a popular architecture for optical see-through augmented reality (AR) devices because they provide a large eyebox while maintaining a compact form factor. However, they typically suffer from some drawbacks, including low optical efficiency and limited image quality, especially toward the edges of the field of view. Low optical efficiency reduces the brightness seen by the user and makes AR devices difficult to use in brighter environments, particularly outdoors. Poor image quality reduces the amount of detail that can be displayed through an AR device, limiting their range of application to showing large text and low-resolution figures. High efficiency and sharp image quality are difficult to achieve simultaneously in waveguide displays, requiring tradeoffs in the design process and the system specifications. In this work, we investigate how these parameters are impacted by the waveguide's geometry and choices about the diffractive gratings used. We show an example of a starting architecture and how to optimize performance by dividing the in-coupler into multiple zones without altering the overall waveguide geometry. Splitting the in-coupler into multiple zones opens a new dimension for exploring and expanding the waveguide design space.
Metaforms are novel optical components formed by conforming a metasurface to a freeform substrate. Metaforms can be a powerful solution when designing compact imaging systems such as augmented reality displays. Given the rotationally variant nature of the metaform substrate and the difficulty of metasurface fabrication on curved substrates, the proper alignment of the metasurface nanofeatures to the freeform substrate is essential. Thus, to seamlessly bridge the metaform design, manufacturing, and metrology, we developed a software tool that automatically generates ISO standard highaccuracy CAD models for the designed metaform components.
The creation of new see-through near-eye displays (NEDs) architectures is a topic of intense research focus. A fundamental problem that each design must address is the field of view (FOV) and eyebox of NEDs are limited by etendue conservation for a fixed display optics size. Waveguide architecture provides the solution to increasing the eyebox in NEDs without increasing the optics size through exit pupil expansion. Brightness and uniformity are two key features of waveguide architecture. In this work, we focus on the brightness of the waveguide since the image uniformity can be compensated by the display engine. We show that the geometry of the waveguide sets a fundamental limit on the in-coupling efficiency for a given FOV. This limit can be used as a tool for waveguide designers to benchmark the in-coupling efficiency of their incoupler gratings. With this derived limit, we designed and optimized a metasurface-based grating (metagrating) and a surface relief grating (SRG) as in-couplers. The diffractive efficiencies of the two types of in-couplers were then compared to the theoretical efficiency limit. The metagrating's 28% efficiency surpasses the SRG's 20% efficiency and nearly matches the geometry-based limit of 29% due to the superior angular response control of metasurfaces compared to SRGs. This work provides a new understanding of the brightness efficiency limit of waveguide-based combiners and paves a novel path toward implementing metasurfaces in efficient waveguide AR displays.
Freeform optics and metasurfaces are two emerging optical technologies that show promise for addressing the needs of modern consumer devices like augmented and virtual reality (AR/VR) displays and mobile cameras. Recent advances in fabrication and testing have been critical to the success of freeform optics. In parallel, various methods for metasurface fabrication, including electron-beam lithography (EBL), have been researched and well established in the last decade but have been limited to fabrication on flat substrates. Metaform is a new optical component that consists of a metasurface conformed to a freeform substrate. We will explore the advances in nodal aberration theory, freeform design methodology, nanofabrication, and metrology necessary to make metaform optics a reality. To validate the developed processes and highlight the advantages of metaforms, we will examine a compact metaform imager inspired by the needs of AR displays. By leveraging the benefits of both metasurfaces and freeform optics, metaforms can thus be used to navigate critical design tradeoffs between optical performance, system volume, and form factor.
Unlike conventional optical components, which often present physical obstructions to the miniaturization of optoelectronic devices, the control of light using flat optics has attracted much recent attention due to unique technological opportunities presented by these devices. Optical metasurfaces, which are composed of rationally designed nanostructures, are proposed to replace some of the conventional optical elements given their compact size and more importantly, the ability to produce spatially varying phase change, amplitude modulation and polarization conversion of incident light over subwavelength dimensions. For example, a compact, flat lens with dynamically tunable focal length will be an essential component in advanced reconfigurable optical systems. Although there have been some successful demonstrations of active metalenses recently, they all work in the transmission configuration. Here, we design and realize the first reflection type, tunable lens (i.e., metamirror) operating in the visible regime (670 nm). With a designed hyperboloidal phase profile, the metamirror is fabricated on a substrate driven by external force, so its focal length can be adjusted dynamically. It is shown that the focal length can be continuously adjusted by up to 45% with a 0 to 20% lateral stretching of the substrate, while maintaining diffraction-limited focusing and high focusing efficiency. Our design as a flat optics element has strong potential in widespread applications such as wearable mixed reality electronics, biomedical instruments and integrated optics devices.
*[email protected] Design study for a 16x zoom lens system for visible surveillance camera Anthony Vella*, Heng Li, Yang Zhao, Isaac Trumper, Gustavo A. Gandara-Montano, Di Xu, Daniel K. Nikolov, Changchen Chen, Nicolas S. Brown, Andres Guevara-Torres, Hae Won Jung, Jacob Reimers, Julie Bentley The Institute of Optics, University of Rochester, Wilmot Building, 275 Hutchison Rd, Rochester, NY, USA 14627-0186 ABSTRACT High zoom ratio zoom lenses have extensive applications in broadcasting, cinema, and surveillance. Here, we present a design study on a 16x zoom lens with 4 groups (including two internal moving groups), designed for, but not limited to, a visible spectrum surveillance camera. Fifteen different solutions were discovered with nearly diffraction limited performance, using PNPX or PNNP design forms with the stop located in either the third or fourth group. Some interesting patterns and trends in the summarized results include the following: (a) in designs with such a large zoom ratio, the potential of locating the aperture stop in the front half of the system is limited, with ray height variations through zoom necessitating a very large lens diameter; (b) in many cases, the lens zoom motion has significant freedom to vary due to near zero total power in the middle two groups; and (c) we discuss the trade-offs between zoom configuration, stop location, packaging factors, and zoom group aberration sensitivity.
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