More Like this

1. High-speed tunable optical absorber based on a coupled photonic crystal slab and monolayer graphene structure

   https://doi.org/10.1364/OE.476763  

   Pan, Mingsen; Liu, Aaron; Liu, Zhonghe; Zhou, Weidong (January 2022, Optics Express)

   Reconfigurable metasurfaces have been pursued intensively in recent years for the ability to modulate the light after fabrication. However, the optical performances of these devices are limited by the efficiency, actuation response speed and mechanical control for reconfigurability. In this paper, we propose a fast tunable optical absorber based on the critical coupling of resonance mode to absorptive medium and the plasma dispersion effect of free carriers in semiconductor. The tunable absorber structure includes a single-layer or bi-layer silicon photonic crystal slab (PCS) to induce a high-Q optical resonance, a monolayer graphene as the absorption material, and bottom reflector to remove transmission. By modulating the refractive index of PCS via the plasma dispersion of the free carrier, the critical coupling condition is shifted in spectrum, and the device acquires tuning capability between perfect absorption and total reflection of the incident monochromatic light beam. Simulation results show that, with silicon index change of 0.015, the tunable absorption of light can achieve the reflection/absorption switching, and full range of reflection phase control is feasible in the over coupling region. The proposed reconfigurable structure has potential applications in remote sensing, free-space communications, LiDAR, and imaging. 

   more » « less
2. Phase change plasmonic metasurface for dynamic thermal emission modulation

   https://doi.org/10.1063/5.0165663  

   Wang, Zexiao; Jing, Lin; Liu, Xiu; Luo, Xiao; Yun, Hyeong Seok; Li, Zhuo; Shen, Sheng (January 2024, APL Photonics)

   Plasmonic metasurfaces with adjustable optical responses can be achieved through phase change materials (PCMs) with high optical contrast. However, the on–off behavior of the phase change process results in the binary response of photonic devices, limiting the applications to the two-stage modulation. In this work, we propose a reconfigurable metasurface emitter based on a gold nanorod array on a VO2 thin film for achieving continuously tunable narrowband thermal emission. The electrode line connecting the center of each nanorod not only enables emission excitation electrically but also activates the phase transition of VO2 beneath the array layer due to Joule heating. The change in the dielectric environment due to the VO2 phase transition results in the modulation of emissivity from the plasmonic metasurfaces. The device performances regarding critical geometrical parameters are analyzed based on a fully coupled electro-thermo-optical finite element model. This new metasurface structure extends the binary nature of PCM based modulations to continuous reconfigurability and provides new possibilities toward smart metasurface emitters, reflectors, and other nanophotonic devices. 

   more » « less
3. Topological Polaritonic Metamaterials Realized in Bulk Transition Metal Dichalcogenide Crystals

   https://doi.org/10.1002/sstr.202500328  

   Guddala, Sriram; Kiriushechkina, Svetlana; Kawaguchi, Yuma; Vakulenko, Anton; Smirnova, Daria; Chand, Saroj B; Hobuss, Edda M; Grosso, Gabriele; Alù, Andrea; Khanikaev, Alexander B (September 2025, Small Structures)

   Due to the enhanced nature of the interactions of light with quantum excitations, topological polaritonic (TP) systems form a unique platform that offers on‐chip control over half‐light, half‐matter excitations via synthetic degrees of freedom. Among other polaritonic platforms, van der Waals materials (vdW) have recently attracted significant interest due to the relative simplicity of their integration into topological photonic structures. Several TP insulators based on vdW materials have been demonstrated; however, they rely on hybrid structures with nanopatterned dielectric substrates, which limit the strength of light‐matter interactions. Here, a monolithic all‐vdW TP insulator based on bulk crystals of transition metal dichalcogenide WS₂is designed and experimentally realized. Due to their high refractive index and the presence of exciton modes, these nanomaterials prove to be excellent platforms for TPs, offering both excellent confinement and strong light‐matter interactions in monolithic structures. The emergence of TP boundary modes is confirmed by Fourier and real‐space imaging, and a dramatic reduction in dissipation is observed at cryogenic temperatures. The proposed monolithic all‐vdW topological insulators, which are characterized by extreme confinement of optical fields and moderate losses, can serve as an alternative to silicon photonics‐based systems in the quest for the development of polaritonic quantum technologies. 

   more » « less
4. Electrically driven reprogrammable phase-change metasurface reaching 80% efficiency

   https://doi.org/10.1038/s41467-022-29374-6  

   Abdollahramezani, Sajjad; Hemmatyar, Omid; Taghinejad, Mohammad; Taghinejad, Hossein; Krasnok, Alex; Eftekhar, Ali A; Teichrib, Christian; Deshmukh, Sanchit; El-Sayed, Mostafa A; Pop, Eric; et al (December 2022, Nature Communications)

   Abstract Phase-change materials (PCMs) offer a compelling platform for active metaoptics, owing to their large index contrast and fast yet stable phase transition attributes. Despite recent advances in phase-change metasurfaces, a fully integrable solution that combines pronounced tuning measures, i.e., efficiency, dynamic range, speed, and power consumption, is still elusive. Here, we demonstrate an in situ electrically driven tunable metasurface by harnessing the full potential of a PCM alloy, Ge₂Sb₂Te₅(GST), to realize non-volatile, reversible, multilevel, fast, and remarkable optical modulation in the near-infrared spectral range. Such a reprogrammable platform presents a record eleven-fold change in the reflectance (absolute reflectance contrast reaching 80%), unprecedented quasi-continuous spectral tuning over 250 nm, and switching speed that can potentially reach a few kHz. Our scalable heterostructure architecture capitalizes on the integration of a robust resistive microheater decoupled from an optically smart metasurface enabling good modal overlap with an ultrathin layer of the largest index contrast PCM to sustain high scattering efficiency even after several reversible phase transitions. We further experimentally demonstrate an electrically reconfigurable phase-change gradient metasurface capable of steering an incident light beam into different diffraction orders. This work represents a critical advance towards the development of fully integrable dynamic metasurfaces and their potential for beamforming applications. 

   more » « less
5. Experimental observation of topological Z2 exciton-polaritons in transition metal dichalcogenide monolayers

   https://doi.org/10.1038/s41467-021-24728-y  

   Li, Mengyao; Sinev, Ivan; Benimetskiy, Fedor; Ivanova, Tatyana; Khestanova, Ekaterina; Kiriushechkina, Svetlana; Vakulenko, Anton; Guddala, Sriram; Skolnick, Maurice; Menon, Vinod M.; et al (December 2021, Nature Communications)

   null (Ed.)

   Abstract The rise of quantum science and technologies motivates photonics research to seek new platforms with strong light-matter interactions to facilitate quantum behaviors at moderate light intensities. Topological polaritons (TPs) offer an ideal platform in this context, with unique properties stemming from resilient topological states of light strongly coupled with matter. Here we explore polaritonic metasurfaces based on 2D transition metal dichalcogenides (TMDs) as a promising platform for topological polaritonics. We show that the strong coupling between topological photonic modes of the metasurface and excitons in TMDs yields a topological polaritonic Z 2 phase. We experimentally confirm the emergence of one-way spin-polarized edge TPs in metasurfaces integrating MoSe 2 and WSe 2 . Combined with the valley polarization in TMD monolayers, the proposed system enables an approach to engage the photonic angular momentum and valley and spin of excitons, offering a promising platform for photonic/solid-state interfaces for valleytronics and spintronics. 

   more » « less