Events

Multispectral Metasurfaces for Pixellated CMOS Sensors

Professor Henri Benisty, Institut d'Optique - Paris Saclay

Presented on Zoom ONLY

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Abstract

Metasurfaces have become a staple of photonics either as stand-alone devices, or more interestingly for us, as a clever layer, typically atop a CMOS pixellated chip. We will advocate that there is a hierarchy of levels: from the metasurface local unit cell, to the pixel to the "multispectral pixel ensemble" (3x3 to 7x7 to set dimensions) to the full chip-size. Such a hierarchy calls for the elaboration of a specific engineering knowledge, which could parallel the hierarchy of microelectronics: transistor, gate, adder, full chip. We will go through the state-of-the art of spectral imaging handling, driven by the ubiquitous Bayer filters, which nevertheless demand improvement, toward various flavours of multi-spectral imaging. We will show metasurface solutions that make good use of CMOS design constraints (few layers, few materials) to perform filters that lend themselves well to spectral retrieval. Specifically, "hybrid Fabry-Perot" will be shown to gather several interesting properties, among which angular tolerance.  Schemes that combine them with the more dispersive Resonant Waveguide Grating (RWG) classical resonances will also be considered, e.g. with the target of retrieving not only the spectrum of a target, but also its angle of incidence, with an accuracy of one degree or so. Compressive sensing techniques that take advantage of regularization techniques will be shown to perform well with 30-40 metasurface filters, retrieving a variety of spectral inputs commonly used in hyperspectral benchmarks. The last part of the talk will be dedicated to the upper "mesoscopic" part of the hierarchy, notably how to mitigate the crosstalk between adjacent pixels at the 1-3 µm scale, without modifying the bank of metasurfaces but by choosing an optimized overall arrangement."

Biography

After training in solid-state physics in 1984, Henri Benisty completed his Paris-6 PhD at the Condensed Matter Physics (PMC) Laboratory at Ecole Polytechnique, Palaiseau, France, followed by a post-doc at Thales TRT, France. He lectured at University of Versailles-Saint-Quentin (1991-2002). During this period, he worked on light confinement and extraction using wavelength-scale structures, especially microcavities and two-dimensional photonic crystals. Since 2002, he is a professor at the Institut d'Optique Graduate School (University Paris-Saclay ) in the Nanophotonics group of the Charles Fabry Laboratory, with interest in parity-time symmetry and metasurfaces in integrated photonics, as well as in non-hermitian complex systems, through multiple collaborations.