This PDF file contains the front matter associated with SPIE Proceedings Volume 12897, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

We report on the experimental observation of chiral resonant modes via a free-space spin-preserving Fabry-Pérot cavity using Pancharatnam-Berry phase reflecting dielectric metasurface mirrors. Such meta-mirrors focus one spin state while diverging the other and preserve the helicity upon reflection.

Design and experimental demonstration of resonant two-dimensional amorphous silicon (a-Si) metasurface supporting mid-infrared quasi-BIC resonances and its application for resonant third harmonic generation enhancement are discussed. Symmetry-protected bound-state-in-continuum resonance is made accessible with the addition of nanodisk couplers in between elliptical dimers with a vertical offset in the symmetry plane. Fabricated quasi-BIC resonant structures show a clear transmission resonance peak at 2470 nm wavelength with a Q-factor of 80. Third-harmonic generation (THG) based up-conversion from 2470 nm fundamental excitation to 823 nm THG shows resonant THG enhancement by 35 times for TM polarized excitation with strong polarization dependence.

Structured-light based 3D sensing technology has been widely used in machine vision, face recognition, and unmanned driving due to high spatial resolution, miniaturized size, large field of view (FOV), and strong anti-interference capability. Speckle structured light is one kind of structure light method. For speckle structured light, certain designed structured projected dot pattern is usually generated by fixed random patterned vertical-cavity surface-emitting laser (VCSEL) array beam duplicated by diffraction optical elements (DOE). This method is conventionally static and non-programmable, resulting in low flexibility. In this paper, a novel programmable structured light is implemented by combining a siliconon-insulator (SOI) reflective metasurface and an individually addressable vertical-cavity surface-emitting laser (VCSEL) array chip. The designed individually addressable VCSEL array is composed of 8 by 8 VCSELs with 100um pitch. These VCSELs share the same cathode, but anodes are separated for on-off switching. The SOI consists of a 3um intermediate SiO2 layer and 340nm Si top layer. Si nanorods are formed by etching the Si top layer. The dimension and rotation of the nanorods are carefully designed so that different VCSEL from the VCSEL array creates speckle pattern with steerable position. By coding the VCSEL on-off states in the VCSEL array, programmable structured light and dynamic speckle density adjustment is achieved. We experimentally demonstrated the new method can get micron level precision which is much better than conventional method. Moreover, great potential is also found for eye movement tracking with the new method. Prototype model for AR/VR glasses application is proposed.

The orbit–orbit interaction of light is the interaction between the intrinsic and extrinsic orbital angular momenta associated with optical vortex beams and varying beam trajectories, respectively. We report the orbit–orbit interaction of light in a plasmonic ellipse cavity, whose unique geometry facilitates vortex–trajectory interplay when a vortex is considered in one of the foci of the ellipse. This interaction, manifested by vortex-dependent shifts, opens a new paradigm for light manipulation by leveraging the manifold vortex states.

Metalenses can be used as standalone single elements or incorporated as one component of a subassembly that also includes other non-metalens optical elements. A ray-based design approach allows the co-design of a hybrid system with metalenses and conventional optics. Such a ray-based design approach is applicable to both polarization-sensitive and -insensitive designs. We validate the ray-based design approach with polarization-sensitive designs.

Active metasurface is attracting a growing amount of attention from industry. Although several potential routes to achieve active metasurface have been proposed, liquid crystal (LC)-based approach, which relies on metasurface immersed in LC environment, is among the most promising methods due to the well-established assembly and packaging processes for LC devices. At the same time, some long-lasting issues of LC devices can be addressed with the introduction of metasurface, such as the slow response speed and limited resolution. In this work, we demonstrate an LC-based active metasurface (LCAM) device with electrically tunable reflection at near-infrared wavelength. The response time was determined to be sub-milliseconds, thanks to the 1-μm cell gap. More importantly, we found that the metasurface also provides alignment for the LC, which potentially could replace the alignment process in conventional LC devices. Our work presents a feasible option to improve the performance of LC-based devices such as liquid crystal on silicon (LCoS).

Metasurfaces, comprising arrays of ultrathin and planar nanostructures (termed "meta-atoms"), hold immense potential for high-performance optical devices, enabling the precise control of electromagnetic waves with subwavelength spatial accuracy. However, the design of meta-atom structures that satisfy multiple functional criteria and workability presents a formidable challenge that significantly increases the design complexity. To address this challenge, we developed an expedited process for constructing a versatile, fabrication-friendly meta-atom library. This process utilizes deep neural networks in conjunction with a meta-atom selector, which considers the practical fabrication limitations. To corroborate the effectiveness of our method, we successfully employed it to empirically validate a dual-band metasurface collimator utilizing intricate free-form meta-atoms.

Metasurface design is often done in one of two distinct ways: at one hand we have full wave based optimization (e.g. adjoint optimization) resulting in a rigorous solution at the expense of very long simulation times and small active areas of a few 10 μm², on the other hand is a library based approach where full wave simulation of individual meta-atoms is combined with local periodic approximation (LPA) based calculations to combine them into a large area meta-surface. The latter approach results in fast calculation and larger areas become possible (mm² to cm²) but with an approximated result. To tackle the approximation issues coming from LPA, we here analyze under which conditions the LPA is no longer valid. Overlapping domain analysis (ODA) has been proposed to improve the accuracy of simulation by accounting for neighbouring meta-atoms without requiring full wave calculation of the entire area at once. We observe specific locations where there are large discrepancies between neighbouring structure forms. Based on this result we propose a workflow for large metasurfaces: 1) LPA based design of the component, 2) ODA to locate the specific regions where LPA approximations are insufficient and 3) optimization of the specific structure on these location based on extended metaatom simulations. We compare the simulation results and calculation time of the following 3 methods: LPA, overlapping domains and full wave FDTD to determine practical areas where each method is appropriate.

Conventional metalens design is based on the library where phases and transmissions of the meta-atoms are calculated with the periodic boundary condition. And the most suitable meta-atom is picked up from the library ignoring its environment. However, the coupling between adjacent meta-atoms produces the phase error, leading to low efficiency and scattering of the metalens. We proposed a method of numerical optimization of the wavefront error by adjusting the meta-atoms size, which reduces phase errors leading to higher efficiency compared to the conventional metalens design. This method is scalable for a large size metalens and for metalens with an arbitrary phase profile.

In this study, we explore the innovative potential of metalenses as a compact and flexible alternative to digital micromirror devices, marking a significant advancement in optical engineering. Specifically, we highlight the use of the phase change material Sb₂Se₃ for its ability to enable swift, reversible, and non-volatile focusing and defocusing actions within the 1550 nm telecom spectrum. The integration of a robust ITO microheater into the lens design enhances its functionality, paving the way for dynamic meta lenses suited for beamforming applications. Through a detailed microfabrication process, we demonstrate a metalens capable of rapid tuning at the 0.1MHz level for focusing and defocusing within the C band communication range, by toggling the phase change material between its amorphous and crystalline states. Experimental results reveal a high contrast ratio for switching of 28.7 dB, underscoring the device’s efficiency and potential in revolutionizing optical component design for telecommunications and beyond.

Large lens apertures are crucial for many emerging metalens applications. For example, it is particularly important in achieving adequate signal to noise ratio in atmospheric monitoring and long-distance laser communications, which often require lens diameters on the order of centimetres in size. Achromatic and multiwavelength large-area metalenses pose unique open research questions. Central to this is the issue of scale. Centimetre scale metalenses must be engineered on both the macro-scale size of the entire lens as well as that of the subwavelength scatterers. The mismatch in scale leads to two main challenges. First, it limits the applicability of freeform inverse design procedures due to the computational domain size. Second, under a traditional design approach individual meta-atoms have constraints on their maximum phase-dispersion values which in turn significantly restrict the diameter of an achromatic single layer lens phase profile for a given numerical aperture (NA). Here we demonstrate non-interacting multilayer Huygens’ metasurfaces as a platform to create centimeter scale multiwavelength metalenses. In this configuration each layer modulates a specific wavelength while achieving high transmittance and low phase disturbance at alternative wavelengths. This significantly eases alignment tolerances and allows each layer to be fabricated as a separate metalens. The operating mechanism, main design considerations and limitations are discussed. An example two-wavelength 0.12 NA metalens operating at 2 and 2.34 μm is then developed using an evolutionary algorithm based inverse design scheme within the locally periodic approximation (LPA). It is simulated using FDTD and numerically characterized.

Optical vector vortex beams provide additional degrees of freedom for spatially distinguishable channels in data transmission. Although several coherent light sources carrying a topological singularity have been reported, it remains challenging to develop a general strategy for designing ultra-small, high-quality photonic nanocavities that generate and support optical vortex modes. Here we demonstrate wavelength-scale, low-threshold, vortex and anti-vortex nanolasers in a C5 symmetric optical cavity formed by a topological disclination. Various photonic disclination cavities are designed and analyzed using the similarities between tight-binding models and optical simulations. Unique resonant modes are strongly confined in these cavities, which exhibit wavelength-scale mode volumes and retain topological charges in the disclination geometries. In the experiment, the optical vortices of the lasing modes are clearly identified by measuring polarization-resolved images, Stokes parameters and self-interference patterns. Demonstration of vortex nanolasers using our facile design procedure will pave the way towards next-generation optical communication systems.

Metasurfaces offer flexibility for expanding functionality and reducing the size of optical systems by providing optical functionality from a flat surface. Previous work has demonstrated a rapid fabrication and testing process for wafers containing multiple 1-centimeter diameter metalenses that can be applied towards mass manufacturing. However, quality feedback was limited to analyzing imaging performance parameters such as the modulation transfer function and focal length. These techniques do not give direct feedback about specific manufacturing errors. Currently, getting this feedback still requires expensive, time-intensive processes such as scanning electron microscope (SEM) measurements or local area interferometry, which tend to have a small field of view. Theoretical investigation suggests that phase errors in the metasurface phase profile result in a shift in diffraction efficiency away from the first order and into the other diffraction orders, zero order, second, third, etc. We exploit this concept to comprehensively characterize metalens performance, including the analysis of standard image quality parameters and extending the study to multiple diffraction orders. An extensive set of measurements of the relative efficiency of the diffraction orders is presented for a set of fabricated metalenses alongside SEM measurements to cross-validate the presence of manufacturing defects. This will establish the extent to which current conventional CMOS processing and manufacturing techniques can be applied to metasurface optics by indicating uniformity and yield characteristics across positions and wafers.

Multispectral sensors such as Ambient Light sensors (ALS) are becoming increasingly popular due to growing concerns for health, environment, and safety. These sensors provide non-intrusive quantitative and qualitative information on the photonic footprints of interest. To meet the demand for mass production, CMOS image sensors (CIS) are a good basis for these devices. Commercial hyperspectral cameras use a generalization of Bayer-like matrix of Fabry-Perot cavities (FPC) as multispectral filters embedded onto a CIS. However, the delicate fabrication of these filters is tedious and leads to a pronounced surface topology. In this study, we demonstrate experimentally that multispectral sensing can be achieved using a hybrid FPC (h-FPC) which is an improved version of the regular FP cavity, that consists of two silicon mirrors, SiO2 spacer, and a sub-wavelength silicon grating at the center of the cavity. These structures were fabricated using a CMOS compatible process and can be integrated into an imager process flow. The h-FPC optical response can be tuned in the near-infrared region (750-950nm) by changing the filling factor of the grating inside the cavity without varying its height, unlike planar FPC. This feature makes the hybrid FPC a more versatile and efficient option for agile multispectral sensing.