Multifunctional volumetric meta-optics for color and polarization image sensors

Abstract

Three-dimensional elements, with refractive index distribution structured at sub-wavelength scale, provide an expansive optical design space that can be harnessed for demonstrating multi-functional free-space optical devices. Here we present 3D dielectric elements, designed to be placed on top of the pixels of image sensors, that sort and focus light based on its color and polarization with efficiency significantly surpassing 2D absorptive and diffractive filters. The devices are designed via iterative gradient-based optimization to account for multiple target functions while ensuring compatibility with existing nanofabrication processes, and experimentally validated using a scaled device that operates at microwave frequencies. This approach combines arbitrary functions into a single compact element even where there is no known equivalent in bulk optics, enabling novel integrated photonic applications.

Fullwave Maxwell inverse design of axisymmetric, tunable, and multi-scale multi-wavelength metalenses

“…For devices operating at shorter wavelengths, thus requiring proportionately smaller feature sizes, the design process would shift to multilayer structures with piecewise-constant cross-section [10,51]. Conversely, at longer wavelengths such as for microwave wavefront shaping, multilayer structures could be straightforwardly fabricated, for instance, by stacking multiple stacks of 3D-printed resins or drilled materials [52].…”

Mechanically reconfigurable multi-functional meta-optics studied at microwave frequencies

“…The three designs presented are all optimized with the same strategy. The optimization technique is similar to the techniques presented in [13,20], with some differences to account for the mechanical reconfiguration of each device, which will be briefly summarized here. The adjoint variable method is a technique to efficiently compute the gradient of a figure of merit with respect to a design region permittivity by combining the results of just two simulations, a "forward" simulation and a backward, or "adjoint", simulation.…”

“…To expand the functionality of metaoptics, adjoint-based topology optimization is capable of designing high-performing dielectric structures with nonintuitive index distributions and objective functions that are challenging to achieve with traditional methods 9,10 . While much of the work has been on 2D platforms such as silicon photonic waveguides 11,12 and at optics 13,14 , free-space 2.5D and 3D devices have also been explored recently [15][16][17][18][19] . In a previous work, a passive 3D device was designed that functions as an red-green-blue (RGB) color splitter and polarizer, scaled up to microwave frequencies 16 .…”

“…While much of the work has been on 2D platforms such as silicon photonic waveguides 11,12 and at optics 13,14 , free-space 2.5D and 3D devices have also been explored recently [15][16][17][18][19] . In a previous work, a passive 3D device was designed that functions as an red-green-blue (RGB) color splitter and polarizer, scaled up to microwave frequencies 16 . An interesting prospect for this type of device is to expand its functionality while minimizing any corresponding reduction in e ciency.…”

Applying Machine Learning to the Optics of Dielectric Nanoblobs

“…[26] Most of the applications of DNN in ID leverage on the creative parameterization of geometries, [27][28][29] while more complex nanostructures can be achieved when an image is used to convey the geometry, e.g., images extracted from electron micrographs, while implementing a generative algorithm to produce new geometries. [30][31][32] Although adjoint-based topology optimization has been effective in solving the inverse problem in photonic structure design [33,34] and is capable of producing complex geometries resembling blobs, [35][36][37][38][39] the process requires an iterative optimization for DOI: 10.1002/adpr.202000068 Dielectric nanostructures are the basic building blocks for photonic metasurfaces exhibiting designer optical responses. As their optical responses are nonintuitive, design procedures often consider only primitive geometries such as circles, ellipses, and rectangles.…”