Please join the Photonics Initiative for a one-hour talk from Qitong Li, titled:
Improved Light-Field Control and Light-Matter Interaction via Optically Resonant Nanostructures for Device Applications
Abstract – The Starting from the 1970s, great efforts have been made to miniaturize bulky optical devices. This progress accelerated significantly over the last decade due to the emerging field of metasurfaces. These planar nanophotonic devices, made from judiciously-engineered, subwavelength-thick optical nano-resonators, are capable of controlling the amplitude, phase, and spectral properties of light waves with subwavelength resolution, and therefore have the potential to replace a wide range of bulk optical elements with flat optics. Given the dimension of these flat optical elements becomes compatible with on-chip electronics, we now foresee an unprecedented opportunity to boost the performance and design novel functionalities for optoelectronic devices via its smart integration with metasurface optical elements. In this talk, I will discuss specifically how to leverage the emergent properties of optically resonant nano-structures to achieve the improved control over the emission, propagation, and absorption of the light-fields at the nanoscale for various device applications, such as photodetectors, reflective displays, and optical modulators.
I will first talk about the radiative nature of Mie-type optical resonances and how it leads to novel optical resonances in a cluster of nano-resonators beyond the chemical bonding model . I will exemplify how this new optical resonance arising from the radiative coupling between arrayed silicon nanowires can be harnessed to remove reflections from dielectric interfaces, while affording spectro-polarimetric detection by extracting resonance-enhanced photocurrents in silicon nanowires . The demonstrated transparent photodetector concept opens up promising platforms for transparent substrates as the base for optoelectronic devices and in situ optical measurement systems.
Next, I will show that the above concept can be extended to further illustrate why metasurface optofluidics, which is comprised of dense arrays of strongly scattering silicon nano-resonators in automatically controlled microfluidic channels, could become the new “ink” in transparent electronic ink-displays . The silicon nanoresonator arrays here function as a metasurface mirror that can provide on-demand resonant electric and magnetic surface currents at optical frequencies. Thanks to the radiative-coupling nature in arrayed silicon nano-resonators, dielectric screening can be used to tune the resonant frequencies and optical quality factors of these surface currents very efficiently, leading to the intensity and spectral tuning of metasurfacecolor-pixels as well as on-demand optical elements.
Finally, I will talk about how to use a silver metasurface top gating pad in a metal-oxide-semiconductor configuration to boost the light-exciton interaction in transition metal dichalcogenide (TMDC) monolayers. Specifically, I will discuss the strategy to tailor the dispersions and the leakage of the surface plasmon polaritons supported by the silver metasurface pad, and how this strong near-field enhancement can amplify the radiative decay rate of excitons by one order of magnitude. As a result, we demonstrate an very efficient monolayer semiconductor (WS2) free-space optical modulator at room temperature, experimentally enabling 10% absolute reflection modulation and 3dB modulation on/off ratio, improving the reflection modulation effect by twenty times as compared with a suspended monolayer of WS2 . We further extend the concept from reflection modulation to dynamic light-field control by designing a blazed silver metasurface grating as the gating pad, where the first order diffraction efficiency of the reflected beam is electrically modulated. The successful integration of nanophotonics with monolayer semiconductor optoelectronic devices paves the way towards multi-functional and ultra-compact hybrid low-dimensional meta-devices.
References:  Qitong Li, Tong Wu, Jorik van de Groep, Philippe Lalanne, and Mark L. Brongersma, “Structural color
from a coupled nanowire pair beyond the bonding and anti-bonding model,” Optica 8, 464-470 (2021).  Qitong Li,
Jorik van de Groep, Yifei Wang, Pieter G. Kik, amd Mark L. Brongersma, “Transparent Multispectral Photodetectors
Mimicking the Human Visual System,” Nature Communications 10, e4982 (2019).  Qitong Li, Jorik van de Groep,
Adam White, Jung-Hwan Song, Scott Longwell, Polly Fordyce, Stephen R. Quake, Pieter G. Kik, and Mark L.
Brongersma, “Metasurface Optofluidics for Dynamic Control of Light Fields,” Submitted (2022).  Qitong Li, JungHwan Song, Fenghao Xu, Jorik van de Groep, Alwin Daus, Jiho Hong, Yan Joe Lee, Eric Pop, Fang Liu, and Mark L.
Brongersma, “A Monolayer Semiconductor Free-Space Optical Modulator,” To be submitted.
Bio – Qitong Li is currently a Ph.D. student under the supervision of Professor Mark L. Brongersma in the department of Materials Science and Engineering at Stanford University. He received his B.Sc. degree in physics from Peking University in 2016. His current research interests are focused on the development of flat optical elements and optoelectronic devices that rely on optically-resonant nanostructures and emerging material platforms to achieve improved control over the emission, propagation, and absorption of light-fields at the nano-scale. He is the recipient of MRS Graduate Student Award (2020), O. Cutler Shepard Award at Stanford University (2020), and Best Oral Presentation Award at MRS Spring Meeting (2022).
The talk will be held in the ASRC Auditorium and broadcast via Zoom. The Zoom link can be accessed here.
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