Gaëtan Lévêque

Moir\'e materials have attracted considerable attention over the past few years due to the rich physical phenomena they enable for classical waves through the introduction of the twist degree of freedom. In this study, we investigate optomechanical interactions in a moir\'e slab waveguide formed by introducing a slight mismatch between the periodicities of two ridge arrays patterned on opposite sides of a waveguide. This design configuration generates a moir\'e pattern that gives rise to flat bands supporting strongly localized optical and acoustic modes with highly confined energy density. The resulting periodic moir\'e simultaneously sustains these photonic and phononic modes with high-quality factors. We analyze the optomechanical interactions in this system by considering both the photoelastic and moving-boundaries coupling mechanisms. Numerical simulations reveal optomechanical coupling rates reaching up to 0.3 THz/nm, enabling efficient phonon-photon interactions within the waveguide. The proposed moir\'e waveguide platform offers substantial tunability of the optical and mechanical modes through control of the arrays mismatch that defines the moir\'e pattern. These results demonstrate the potential of moir\'e waveguide architectures for realizing high-quality optomechanical cavities with strong acoustooptical interaction.

Global energy challenges establish building‐integrated photovoltaics as a pivotal decarbonization frontier, where semitransparent organic photovoltaics (ST‐OPVs) represent a promising technology for simultaneous power generation and daylight transmission. However, their widespread application is constrained by a fundamental efficiency and transparency trade‐off governed by complex photon management. Herein, we introduce a physics‐enhanced deep learning (PDL) framework that embeds optical physical priors into neural network, significantly reducing the reliance on extensive experimental datasets while enhancing predictive accuracy beyond conventional simulation and purely data driven methods. Building on a novel halogen‐additive engineering strategy, that enables opaque devices with a power conversion efficiency exceeding 20%, our PDL‐guided optimal optical design delivers corresponding ST‐OPVs with a record light utilization efficiency of 6.09%. When scaled to large‐area manufactured modules, multi‐scale building energy modeling demonstrates that the nationwide deployment of such ST‐OPVs could meet up to one‐fifth of China's total energy demand, highlighting their transformative potential in advancing sustainable energy systems and supporting global carbon neutrality goals.

Semitransparent organic solar cells (ST‐OSCs) offer significant potential for building‐integrated energy harvesting combined with daylight transmission. However, simultaneously achieving high power conversion efficiency (PCE) and perceptually accurate color rendition remains challenging. This work introduces high‐throughput optical design for developing human vision‐adapted ST‐OSCs with spectrally targeted color perception, advancing the realization of polychromatic urban architecture. First, a dual‐additive method is developed to enhance phase separation within the PEDOT:PSS, yielding a PCE of 20.0% in opaque devices. Building upon this, high‐throughput optical design enables the optimization of Fabry–Pérot microcavity structures for precise color generation. The core framework evaluates PCE, infrared rejection rate (IRR), and the novel Visual Match Index (VMI) simultaneously to assess spectral alignment with human visual sensitivity. ST‐OSCs engineered to match the peak sensitivities of short‐, middle‐, and long‐wavelength cone cells are fabricated, achieving VMI of 0.99, 0.93, and 0.90, respectively, while maintaining a PCE > 16% and an IRR > 98%. City‐scale energy modeling incorporating the experimental parameters predicts that deploying these ST‐OSCs as colored facades across Shanghai could deliver substantial power generation while significantly reducing cooling loads. Overall, this work establishes human‐centric, aesthetically tunable ST‐OSCs as multifunctional building elements that harmoniously integrate visual comfort with urban energy sustainability.

Semitransparent organic photovoltaics (ST‐OPVs) hold great promise for building‐integrated applications but encounter a critical trade‐off between power conversion efficiency (PCE) and visible transparency. This work addresses this challenge by introducing a novel theoretical framework that synergistically combines optical modeling and material design. A piecewise Gaussian absorption model has been developed to accurately simulate asymmetric spectral characteristics of organic materials. This model enables the virtual screening of potential organic donor‐acceptor configurations, identifying two optimal configurations: a narrow‐narrow (N + N) system and a wide‐narrow (W + N) system, which achieve a superior balance between PCE and transparency. High‐throughput optical screening of bilayer coupling layers further enhances light utilization efficiency to 9.8% (N + N) and 9.3% (W + N) through optimized light management. This study bridges material properties and optical engineering, providing a predictive tool for ST‐OPV optimization to guide the development of high‐performance, visually transparent solar technologies.

We theoretically study a random arrangement of cylindrical gold nanoparticles (NPs) deposited on a dielectric/gold substrate as a potential plasmonic physically unclonable function (PUF). We use the coupled dipole approximation (CDA) method in order to reduce the computation time and memory demand. Each NP is modeled as a single electric dipole through the polarizability tensor of a spheroidal-shaped NP, while the interparticle coupling is described by Green’s tensors. The concept of plasmonic PUF considered here consists of transforming the electric field maps obtained by the CDA into 2D-binary matrices using a key generation algorithm. A PUF must satisfy different criteria to be efficient, including uniqueness that is evaluated by the distributions of Hamming inter-distances. In this work, we propose to evaluate the uniqueness property of different PUFs characterized by substrates whose dielectric layer thickness is variable. We also test the ability to generate unique keys when the challenges to which our PUF concept is subjected change, namely, the wavelength, angle, and plane of incidence.

Valley photonic crystals provide efficient designs for the routing of light through channels in extremely compact geometries. The topological origin of the robust transport and the specific geometries under which it can take place have been questioned in recent studies. In this article, we introduce a design for valley photonic crystals with richer arrangement possibilities than the standard valley photonic crystals based on two holes of different sizes in the unit cell. Our approach is based on the permutation of three sets of rhombi in a hexagonal lattice to investigate the interplay between Berry curvature, valley Chern number, and chirality of interfaces to achieve robust edge-modes propagation along domain walls. We study three types of interfaces with different symmetries: the non-chiral interface with glide-mirror symmetry commonly used in honeycomb-type valley crystals, and two chiral interfaces with or without inversion symmetry of the adjacent bulk lattices. In the latter case, no valley topology is expected. We show that for the three families, edges preserving the shape of the interface through 120° sharp corners can sustain edge-modes with comparable robustness. Moreover, interfaces with glide-mirror symmetry offer promising performances in circuits with more exotic configurations, like 60° and 90° corners or arbitrary curves in which valley preservation is not guaranteed. Our work raises questions about the topological origin of the robustness of transport in valley photonic crystals, discusses the role of the chirality of the interfaces in the propagation around sharp corners, and provides a lattice scheme with broad design possibilities.

Valley photonic crystals provide efficient designs for the routing of light through channels in extremely compact geometries. The topological origin of the robust transport and the specific geometries under which it can take place have been questioned in recent works. In this article, we introduce a design for valley photonic crystals with richer arrangement possibilities than the standard valley photonic crystals based on two holes of different sizes in the unit cell. Our approach is based on the permutation of three sets of rhombi in an hexagonal lattice to investigate the interplay between Berry curvature, valley Chern number and chirality of interfaces to achieve robust edge-modes propagation along domain walls. We study three types of interfaces with different symmetries: the non-chiral interface with glide-mirror symmetry commonly used in honeycomb-type valley crystals, and two chiral interfaces with or without inversion symmetry of the adjacent bulk lattices. In the latter case, no valley topology is expected. We show that for the three families, edges preserving the shape of the interface through 120° sharp corners can sustain edge-modes with comparable robustness. Moreover, interfaces with glide-mirror symmetry offer promising performances in circuits with more exotic configurations, like 60° and 90° corners or arbitrary curves in which valley preservation is not guaranteed. Our work raises questions about the topological origin of the robustness of transport in valley photonic crystals, discusses the role of the chirality of the interfaces in the propagation around sharp corners, and provides a lattice scheme with broad design possibilities.

The realization of integrated, low-loss, and efficient systems for data-intensive applications such as augmented and virtual reality requires on-chip integrated photonic circuits, which have great potential for advanced information and communication technologies, including 6G wireless networks and intra- and inter-chip communication systems. A promising platform for achieving this revolution is Valley Photonic Crystals (VPCs). VPCs enable the construction of topological interfaces, which facilitate the propagation of light with minimal losses and backscattering through unidirectional edge modes. Interfacial topological interfaces and the degree of topological protection experienced by these robust edge modes is a relatively new perspective worth exploring. The ever-increasing demand for faster data rates in data-intensive applications like augmented and virtual reality necessitates the exploration of frequencies beyond the conventional 300 GHz band. In this study, we introduce variations in topological protection by considering different interfacial designs and suitable air-hole geometries for passive functional devices. We show that the partial breakup of topological protection can be an asset for the design of on-chip passive functionalities. We focus on bearded and zigzag junctions and appropriate air hole geometries for VPC unit cells. To experimentally verify the scalability of topological protection, we demonstrate the performance of terahertz (THz) topological ring resonators and THz double cavity resonators designed for operation in the 600 GHz frequency region. This work showcases how the scaling of topological protection can be achieved by utilizing a combination of air hole geometry and interfacial degrees of freedom, providing functional tuning of devices at the chip level.

In this work, we propose a sensor based on Tamm plasmonic resonance; the structure is composed of gold nanoribbons deposited on a Distributed Bragg Reflector (DBR) (SiO₂/Si₃N₄)₆. We have enhanced the sensitivity of our sensor from 40 nm/RIU to 200 nm/RIU for a refractive index change of 1% by replacing the last layer of Si₃N₄ in contact with gold with porous Si₃N₄ with a porosity of p = 40%.

In this paper, the ability of a metasurface made of resonant elliptical pillars to focus flexural Lamb waves in the sub-wavelength regime is investigated. We report on the influence of the ellipticity parameter on the local resonances of the pillars, in particular the monopolar compressional and dipolar bending modes that are responsible for the desired focusing effect. We also discuss how the transmission through a line of pillars reveals these modes when the orientation of the pillars is changed with respect to the incident wave. Both the resonances can be superimposed for a particular choice of the ellipticity parameter, allowing a phase shift of 2π in the transmission coefficient for an incident antisymmetric Lamb wave, which is a necessary condition for the design of the metasurface. Finally, a gradient design for the pillar ellipticity is investigated, and its capacity to choose the focusing directionality of the transmitted wave at different targeted points is demonstrated.