Tunable Infrared Optical Switch Based on Vanadium Dioxide

A tunable infrared optical switch based on a plasmonic structure consisting of aluminum nanoarrays with a thin film of vanadium dioxide is proposed. This optical switch can realize arbitrary wavelength-selective optical switching in the mid-infrared region by altering the radii of the aluminum nanoarrays. Furthermore, since vanadium dioxide transforms from its low-temperature insulator phase to a high-temperature metallic phase when heated or applied voltage, the optical switch can achieve two-way switching of its “ON” and “OFF” modes. Finite-difference time-domain software is used to simulate the performance of the proposed infrared optical switch. Simulation results show that the switch offers excellent optical performances, that the modulation depth can reach up to 99.4%, and that the extinction ratio exceeds −22.16 dB. In addition, the phase transition time of vanadium dioxide is on the femtosecond scale, which means that this optical switch based on a vanadium dioxide thin film can be used for ultrafast switching.

Tunable GaAs metasurfaces for ultrafast image processing

The design and construction of optical semiconductor metasurfaces for various applications have become an important topic in the last decade. However, most metasurfaces are static; they are optimized for only one exact purpose and typically realize only one operation. In this work, we discuss the basic methods for creating dynamic metasurfaces giving special attention to ultrafast optical switching and provide numerical modeling of metasurfaces made of GaAs material realizing different amplitude-phase profiles under asymmetrical optical pumping. The metasurfaces are composed of semiconductor discs immersed in a fused silica medium. We demonstrate that based on Fourier transform and spatial filtering methods, these structures can be used for image processing and optical computing. Ultrafast switching is achieved by using an optical pump-probe scheme. The characteristic relaxation times between the pumped state and the relaxed state are on the order of several picoseconds.

Nanoscale self-organisation in Mott insulators: a richness in disguise

Mott transitions in real materials are first order and almost always associated with lattice distortions, both features promoting the emergence of nanotextured phases. This nanoscale self-organization creates spatially inhomogeneous regions, which can host and protect transient non-thermal electronic and lattice states triggered by light excitation. However, to gain full control of the Mott transition for potential applications in the field of ultrafast switching and neuromorphic computing it is necessary to develop novel spatial and temporal multiscale experimental probes as well as theoretical approaches able to distill the complex microscopic physics into a coarse-grained modelling. Here, we combine time-resolved X-ray microscopy, which snaps phase transformations on picosecond timescales with nanometric resolution, with a Landau-Ginzburg functional approach for calculating the strain and electronic real-space configurations. We investigate V2O3, the archetypal Mott insulator in which nanoscale self-organization already exists in the low-temperature monoclinic phase and strongly affects the transition towards the high-temperature corundum metallic phase. Our joint experimental-theoretical approach uncovers a remarkable out-of-equilibrium phenomenon: the photoinduced stabilisation of the long sought monoclinic metal phase, which is absent at equilibrium and in homogeneous materials, but emerges as a metastable state solely when light excitation is combined with the underlying nanotexture of the monoclinic lattice. Our results provide full comprehension of the nanotexture dynamics across the insulator-to-metal transition, which can be readily extended to many families of Mott insulating materials. The combination of ultrafast light excitation and spatial nanotexture turns out to be key to develop novel control protocols in correlated quantum materials.

All-Solid-State Proton-Based Tandem Structure Achieving Ultrafast Switching Electrochromic Windows

All-solid-state electrochromic devices (ECDs) for smart-window applications currently suffer from limited ion diffusion speed, which lead to slow coloration and bleaching processes. Here, we design an all-solid-state tandem structure with protons as diffusing species achieving an ultrafast switching ECD. We use WO3 as the electrochromic material, while poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) as the solid-state proton source to enable fast switching. This structure by itself exhibits low optical modulation (i.e., difference of on/off transmittance). We further introduce a solid polymeric electrolyte layer on top of PEDOT:PSS to form a tandem structure, which provides Na+ ions to PEDOT:PSS and pump protons there to the WO3 layer through ion exchange. Our new all-solid-state ECD features high optical modulation (>92% at 650 nm), fast response (coloration to 90% in 0.7 s and bleaching to 65% in 0.9 s and 90% in 7.1 s) and excellent stability (<10% degradation after 3000 cycles). Large-area (30×40 cm2) as well as flexible devices are fabricated to demonstrate the great potential for scaling up.

Ultrafast Switching and Linear Conductance Modulation in Ferroelectric Tunnel Junctions via P(VDF-TrFE) Morphology Control

Neuromorphic computing architectures demand development of analog, non-volatile memory components operating at femto-Joule/bit operation energy. Electronic components working at this energy range require devices operating at ultrafast timescales. Among different...

Single nanoflake-based PtSe2 p–n junction (in-plane) formed by optical excitation of point defects in BN for ultrafast switching photodiodes

Here, novel lateral PtSe2 p–n junctions are fabricated based on the PtSe2/BN/graphene (Gr) van der Waals heterostructures upon the illumination of visible light via the optical excitation of the mid-gap point defects in hexagonal boron nitride (h-BN).