Brochosome-inspired binary metastructures for pixel-by-pixel thermal signature control.

Microscale thermal signature control using incoherent heat sources remains challenging, despite recent advancements in plasmonic materials and phase-change materials. Inspired by leafhopper-generated brochosomes, we design binary metastructures functioning as pixel twins to achieve pixelated thermal signature control at the microscale. In the infrared range, the pixel twins exhibit distinct emissivities, creating thermal counterparts of "0-1" binary states for storing and displaying information. In the visible range, the engineered surface morphology of the pixel twins ensures similar scattering behaviors. This renders them visually indistinguishable, thereby concealing the stored information. The brochosome-like pixel twins are self-emitting when thermally excited. Their structure-enabled functions do not rely on the permittivities of specific materials, which distinguishes them from the conventional laser-illuminated plasmonic holographic metasurfaces. The unique combination of visible camouflage and infrared display offers a systemic solution to microscale spatial control of thermal signatures and has substantial implications for optical security, anticounterfeiting, and data encryption.

Placement Method of Multiple Lidars for Roadside Infrastructure in Urban Environments.

Sensors on autonomous vehicles have inherent physical constraints. To address these limitations, several studies have been conducted to enhance sensing capabilities by establishing wireless communication between infrastructure and autonomous vehicles. Various sensors are strategically positioned within the road infrastructure, providing essential sensory data to these vehicles. The primary challenge lies in sensor placement, as it necessitates identifying optimal locations that minimize blind spots while maximizing the sensor's coverage area. Therefore, to solve this problem, a method for positioning multiple sensor systems in road infrastructure is proposed. By introducing a voxel grid, the problem is formulated as an optimization challenge, and a genetic algorithm is employed to find a solution. Experimental findings using lidar sensors are presented to demonstrate the efficacy of this proposed approach.

Angstrom-Scale Active Width Control of Nano Slits for Variable Plasmonic Cavity.

Nanogap slits can operate as a plasmonic Fabry-Perot cavity in the visible and infrared ranges due to the gap plasmon with an increased wavenumber. Although the properties of gap plasmon are highly dependent on the gap width, active width tuning of the plasmonic cavity over the wafer length scale was barely realized. Recently, the fabrication of nanogap slits on a flexible substrate was demonstrated to show that the width can be adjusted by bending the flexible substrate. In this work, by conducting finite element method (FEM) simulation, we investigated the structural deformation of nanogap slit arrays on an outer bent polydimethylsiloxane (PDMS) substrate and the change of the optical properties. We found that the tensile deformation is concentrated in the vicinity of the gap bottom to widen the gap width proportionally to the substrate curvature. The width widening leads to resonance blueshift and field enhancement decrease. Displacement ratio ((width change)/(supporting stage translation)), which was identified to be proportional to the substrate thickness and slit period, is on the order of 10-5 enabling angstrom-scale width control. This low displacement ratio comparable to a mechanically controllable break junction highlights the great potential of nanogap slit structures on a flexible substrate, particularly in quantum plasmonics.

Effective-zero-thickness terahertz slot antennas using stepped structures.

Metallic nanostructures play an essential role in electromagnetic manipulations due to the localization and enhancement of electromagnetic waves in nanogaps. Scaling down the dimensions of the gap, such as the gap width and the thickness, is an effective way to enhance light-matter interaction with colossal field enhancement. However, reducing the thickness below 10 nanometers still suffers from fabrication difficulty and unintended direct transmission through metals. Here, we fabricate effective-zero-thickness slot antennas by stepping metals in the vicinity of the gaps to confine electromagnetic waves in tiny volumes. We analyze and simulate terahertz transmission, and demonstrate the absorption enhancement of molecules in the slot antennas. Our fabrication technique provides a simple but versatile tool for maximum field enhancement and molecular sensing.

Topology-Changing Broadband Metamaterials Enabled by Closable Nanotrenches.

One of the most straightforward methods to actively control optical functionalities of metamaterials is to apply mechanical strain deforming the geometries. These deformations, however, leave symmetries and topologies largely intact, limiting the multifunctional horizon. Here, we present topology manipulation of metamaterials fabricated on flexible substrates by mechanically closing/opening embedded nanotrenches of various geometries. When an inner bending is applied on the substrate, the nanotrench closes and the accompanying topological change results in abrupt switching of metamaterial functionalities such as resonance, chirality, and polarization selectivity. Closable nanotrenches can be embedded in metamaterials of broadband spectrum, ranging from visible to microwave. The 99.9% extinction performance is robust, enduring more than a thousand bending cycles. Our work provides a wafer-scale platform for active quantum plasmonics and photonic application of subnanometer phenomena.