With the proliferation of networked sensors and artificial intelligence, there is an increasing need for edge computing where data is processed at the sensor level to reduce bandwidth and latency while still preserving energy efficiency. In this talk, I will discuss how meta-optics can be used to implement computation for optical edge sensors, serving to off-load computationally expensive convolutional operations from the digital platform, reducing both latency and power consumption. I will discuss how meta-optics can augment, or replace, conventional imaging optics in achieving parallel optical processing across multiple independent channels for identifying, and classifying, both spatial and spectral features of objects.
In this talk I will explore the hidden potential of electrochemically actuated metasurfaces. Electrochemical actuation is unique in that it provides for control over both the volume expansion of a scatterer as well as the free electron density for permittivity control. I will explore this freedom in dynamic tuning of titanium dioxide and silicon-based metasurfaces, materials already popularized in the field of photonics for their high index and low loss throughout the visible spectrum. Using these materials, we leverage electrochemical intercalation of lithium to initiate phase changes in a continuously tunable, reversible, and bi-stable manner, using bias voltages that are an order of magnitude less than similar devices.
The high computational demand of deep neural networks for computer vision must be alleviated by hardware-based strategies to facilitate applications in resource constrained systems. A potential solutions is to offload computations onto a front-end analog optical preprocessor, which could perform low-level feature encoding operations instantaneously as images are captured. To that end, this study showcases incoherent, broadband, low-noise optical edge encoding for thermal imaging of real-world scenes, which is achieved using a hybrid system of a 24-mm, inversely-designed metasurface and a refractive lens. Using an inverse design approach, the metasurface is optimized for Laplacian-based edge detection across the 7.5 – 13.5 µm LWIR imaging band. This work could be expanded to enable optically-encoded feature maps for accelerating convolutional neural networks for image segmentation and classification.
We demonstrate meta-optic based accelerators that can off-load computationally expensive operations into high-speed and low-power optics. The key to these architectures are the new freedoms afforded by metasurfaces such as optical edge isolation, polarization discrimination, and the ability to spatially multiplex, and demultiplex, information channels. I will discuss how these freedoms can be utilized for accelerating optical segmentation networks and objection classifiers, both based on incoherent illumination. This approach could enable compact, high-speed, and low-power image and information processing systems for a wide range of applications in machine-vision and artificial intelligence.
In this talk I will explore the hidden potential of electrochemically actuated metasurfaces. Electrochemical actuation is unique in that it provides for control over both the volume expansion of a scatterer as well as the free electron density for permittivity control. I will explore this freedom in dynamic tuning of titanium dioxide and silicon-based metasurfaces, materials already popularized in the field of photonics for their high index and low loss throughout the visible spectrum. Using these materials, we leverage electrochemical intercalation of lithium to initiate phase changes in a continuously tunable, reversible, and bi-stable manner, using bias voltages that are an order of magnitude less than similar devices.
We explore three types of advanced optical components for use in EO/IR systems. Freeform, GRIN, and meta- optics and combinations of all three used in various system designs are being studied to develop a trade space road map for future utilization. The emphasis is on SWAP benefits while maintaining or improving performance compared to existing systems.
We demonstrate meta-optic based accelerators that can off-load computationally expensive operations into high-speed and low-power optics. The key to these architectures are the new freedoms afforded by metasurfaces such as optical edge isolation, polarization discrimination, and the ability to spatially multiplex, and demultiplex, information channels. I will discuss how these freedoms can be utilized for accelerating optical segmentation networks and objection classifiers, both based on incoherent illumination. This approach could enable compact, high-speed, and low-power image and information processing systems for a wide range of applications in machine-vision and artificial intelligence.
Dynamic tuning of metamaterials is a critical step towards achieving advanced functionality and improved operational bandwidth. Approaches to modulation can be separated into two categories. The first is mechanical reconfiguration of the scatterer geometry or scatterer arrangement. The second is manipulation of the optical properties of the scatterer, or its environment. Although there are a variety of paths to achieve modulation, electrochemical actuation provides a method that can belong to both categories by providing for both volume expansion through lattice rearrangement as well as modulation of free electron density for permittivity control. In this talk we will outline several approaches towards electrochemical modulation including modulation of popular metasurface materials such as silicon and titanium oxide. The use of nanostructured metasurfaces allow for new freedom in controlling the spectral response of the material while also minimizing diffusion lengths for higher speed and lower power operation compared to traditional electrochromic materials.
Image processing has become a critical technology in a variety of science and engineering disciplines. While most image processing is performed digitally, optical analog processing has the advantages of being low-power and high-speed though it requires a large volume. Meta-optics provide the advantage of thin form factor optics while also allowing complex transfer functions to be employed. In this talk, I will discuss the use of meta-optics for applications in image processing. Specifically, I will discuss meta-optic pre-filters including edge filters as well as filters for identifying higher level spatial features. These meta-optics are designed in conjunction with the digital system and I will discuss how co-design can make the hybrid optical / digital system more tolerant to deterministic and stochastic noise. These analog optical operations can be used to replace, or augment, digital processes for increasing speed while reducing power consumption.
Photodetectors harnessing hot carrier generation on surface plasmon resonant nanoantennas are a promising avenue to achieving sub-bandgap imaging at room temperature. However, efficient extraction of plasmonic hot carriers under low-energy infrared (IR) excitation predicates careful design of Schottky interfaces. This work reports on the simulation-guided fabrication of Au (i) planar diodes and (ii) embedded IR nanoantennas interfaced with both n-/p-type Si and GaAs semiconductors in order to elucidate the impact of their electronic properties on photocurrent generation.
Image processing has become a critical technology in a variety of science and engineering disciplines. While most image processing is performed digitally, optical analog processing has the advantages of being low-power and high-speed. Here, we demonstrate optical analog imaging processing using flat optics including multi-layer architectures. The use of flat meta-optics opens new doors in optical image processing, such as edge imaging filters, as well as the freedom to spatially multiplex optical functions for off-loading processing tasks from the digital system.
The differentiator consists of carefully designed 2D photonic crystal (PhC) slab that can transform an image into its second-order derivative. Based on interference between the direct transmission and low quality factor quasi-guided modes, the PhC slab exhibits angular-dependent transmission for P polarization but remains reflective for S polarization, which avoids polarization mixing in the transmission matrix. Fourier imaging was carried out showing a quadratic transfer function for an NA up to 0.315, which allows one to resolve features on the scale of 1.94λ. To showcase practical applications, the nanophotonic differentiator was directly integrated into an optical microscope and onto a camera sensor demonstrating the ease at which it can be vertically integrated into existing imaging systems. Furthermore, we demonstrate a compound bilayer flat optical by integrating the differentiator with a metalens for realizing a compact and monolithic image processing system. In all cases, the use of the nanophotonic differentiator allows for a significant reduction in size compared to traditional systems as one does not need to pass through the Fourier plane for performing complex image processing. This freedom should open new doors for optical analog image processing in applications involving machine vision.
In this talk, I will present a multilayer all-dielectric metasurface architecture with the goal of increasing the design landscape of metaoptics. The layers are fabricated separately and then combined allowing for various combinations of unit cell geometries. This ultimately allows for independent control over any two properties; amplitude, phase, and polarization. The approach can also allow any of these properties to be independently designed at two wavelengths. This freedom is used to realize metaoptics with a wide range of functionalities including multiwavelength holograms and lenses as well as 3D holograms. I will also discuss how this design freedom can be used for realizing metaoptics for optical computing.
It is two decades since the first reports that the insulator-to-metal transition (IMT) in vanadium dioxide (VO2) occurred on an ultrafast time scale, followed by growing interest in the potential use of this strongly correlated oxide in a variety of switching schemes. At first glance, VO2 would seem to be ideally suited to a variety of applications in electro-optics and all optical switching: The IMT occurs on a sub-picosecond time scale; it is fully reversible and has a large dielectric contrast at wavelengths in the near- to mid-infrared; and the material itself is fully compatible with many optical and electronic materials of interest. However, there are also well-known difficulties, chief among them the fact that the IMT, if fully completed, is accompanied by a structural phase transition (SPT) that requires nanoseconds to return from the rutile, metallic state to the monoclinic insulating ground state – thus essentially limiting switching speeds to time scales similar to those in amorphous-to-crystalline transitions in chalcogenide glasses. Here we discuss the ways in which the very considerable advantages of VO2 as a modulating or threshold switch can be amplified by deploying it appropriately in silicon photonic modulators, switchable metasurfaces, plasmonic heterostructures, and two-dimensional materials that can support phonon polariton optics. We focus particularly on ways of tailoring the physical properties of the VO2 component of a system to meet the requirements of operating in particular wavelength regions, meeting specific threshold requirements and choosing electrical or optical initiation of the IMT.
Vanadium Dioxide is an optically dense phase change material that has been applied to modulating the resonances of plasmonic structures resonant in the THz, infrared and optical ranges. It has been shown previously that fabrication of optical antennas on thin films of Vanadium Dioxide can result in a resonance shift of more than 10% across the phase change. This post-fabrication, dynamic tuning mechanism has the potential to significantly increase the possible applications of plasmonic devices.
Here, we show that optical antenna arrays fabricated on differing thicknesses of Vanadium Dioxide supported by a silicon substrate show a dependence of their resonant wavelengths on this thickness. Along with the geometry of the antennas in the arrays this constitutes an additional degree of freedom in the design of the tuning range of these devices, offering further potential for optimisation of this mechanism. The potential extra blue-shift provided by optimising this thickness may be used, for example, in lieu of reducing antenna dimensions to avoid increasing antenna absorption and the additional plasmonic heating that can result.
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