#metasurfaces

Record-breaking photodetector captures light in just 125 picoseconds

Record-breaking ultrathin photodetector captures light across the entire spectrum in just 125 picoseconds, opening the door to powerful new imaging technologies.

Electrical engineers at Duke University have created the fastest pyroelectric photodetector ever demonstrated, a device that detects light by sensing the tiny amount of heat it produces when absorbed. The ultrathin sensor can capture light across the entire electromagnetic spectrum. It operates at room temperature, requires no external power source, and can be integrated directly into on-chip systems. The technology could eventually enable a new generation of multispectral cameras with applications in areas such as skin cancer detection, food safety monitoring, and large scale agriculture. The findings were reported in the journal Advanced Functional Materials.

Metasurface Enables Advance in Solar Telescope

Metasurfaces—artificial 2D planar surfaces that consist of subwavelength metallic or dielectric nanostructures—offer better, more efficient light control than conventional optical devices. Although researchers have successfully created ultrathin optical components like flat mirrors, lenses and waveplates using metasurfaces, most work remains in the proof-of-concept stage. Now, researchers in the United States have leveraged recent advancements in metasurface optics to improve astronomical instrumentation to make quantitative observations of the sun’s magnetic field (Sci. Adv., doi: 10.1126/sciadv.aee8035). The Solar Imaging Metasurface Polarimeter (SIMPol) is a first-of-its-kind refractive telescope for snapshot imaging polarimetry of the sun enabled by a high-­performance metasurface polarization-analyzing grating.

Ultra-thin metasurface chip turns invisible infrared light into steerable visible beams

The invention of tiny devices capable of precisely controlling the direction and behavior of light is essential to the development of advanced technologies. Researchers at the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC) have taken a significant step forward with the development of a metasurface that can turn invisible infrared light into visible light and aim it in different directions—without any moving parts. The details of their work are explained in a paper published in the journal eLight. The novel metasurface is constructed of an ultra-thin chip patterned with tiny structures smaller than the wavelength of light. When hit with an infrared laser, the chip converts the incoming light to a higher color (or frequency) and sends the new light out as a narrow beam that can be steered simply by changing how the incoming light is polarized. In their experiments, the team converted infrared light around 1530 nanometers—similar to the light used in fiber-optic communications—into visible green light near 510 nanometers and steered it to chosen angles.

Active thermal metasurfaces amplify heat signatures by a factor of nine

Light undergoes a unique phenomenon called superscattering, an optical illusion where a very small object scatters far more light than expected. This happens when multiple scattering modes overlap and interact, allowing tiny objects to scatter far more light than their size should allow. Scientists have now found a way to expand the scope of superscattering beyond optics into the thermal world. A team of researchers from Taiyuan University of Technology, China, has experimentally demonstrated thermal superscattering by surrounding an object with an active shell comprising arrays of controllable heating and cooling elements along its boundary. This shell allowed the tiny object to fake the thermal signatures of an object nine times larger than itself.

Precision-engineered surface can enhance silicon solar cell performance

Converting sunlight into electricity is the task of photovoltaic solar cells, but nearly half the light that reaches a flat silicon solar cell surface is lost to reflection. While traditional antireflective coatings help, they only work within a narrow range of light frequency and incidence angles. A new study may have overcome this limit. As reported in Advanced Photonics Nexus, researchers have proposed a new type of antireflective coating using a single, ultrathin layer of polycrystalline silicon nanostructures (a.k.a. a metasurface). Achieving minimal reflection across certain wavelengths and angles, the metasurface was reportedly developed by combining forward and inverse design techniques, enhanced by artificial intelligence (AI). The result is a coating that sharply reduces sunlight reflection across a wide range of wavelengths and angles, setting a new benchmark for performance with minimal material complexity.

Spin-controlled generation of a complete polarization set with randomly interleaved plasmonic metasurfaces

Optical metasurfaces are finely crafted two-dimensional artificial nanostructures composed of meticulously designed arrays of ultrathin artificial atoms. These surfaces possess capabilities beyond natural materials, enabling multifunctional control of electromagnetic waves. By designing the shape, size, rotation, and position of these artificial atoms, optical metasurfaces can precisely manipulate electromagnetic waves at subwavelength spatial resolutions, offering vast potential applications in the field of photonics. Among the many applications, the control of polarization states using optical metasurfaces has been extensively studied. The development of polarization-encoded multifunctional metasurfaces represents a significant leap in optical technology, allowing a wider range of functions to be integrated into a single metasurface.

A novel liquid crystal-based tunable dielectric metasurface

Dielectric metasurfaces represent one of the cutting-edge research and application directions in optics. They not only possess the advantage of low loss but also enable the realization of device thicknesses at subwavelength scales. Moreover, they can freely modulate light in multiple dimensions, such as amplitude, phase, and polarization. This capability, which traditional optics lacks, holds significant importance for the integration, miniaturization, and scaling of future optical systems. Consequently, dielectric metasurfaces have attracted increasing industrial attention. In a study published in the journal Advanced Devices & Instrumentation, Professor Daping Chu's team at the University of Cambridge developed a novel liquid crystal-based tunable dielectric metasurface. By leveraging the dielectric metasurface's inherent alignment effect on liquid crystals on top of its electrically controllable properties, the need for liquid crystal alignment layer materials and related processes is eliminated, thus saving device manufacturing time and costs. This has practical implications for devices such as liquid crystal on silicon (LCoS).

The expression "flawless from every angle" is commonly used to characterize a celebrity's appearance. This doesn't simply imply that they appear attractive from a specific viewpoint, but rather that their appeal remains consistent and appealing from various angles and perspectives. Recently, a research team from Pohang University of Science and Technology (POSTECH) has employed metasurface to fabricate angle-dependent holograms with multiple functions, capturing significant interest within the academic community. A research team comprising Professor Junsuk Rho from the Department of Mechanical Engineering and the Department of Chemical Engineering and PhD candidate Joohoon Kim from the Department of Mechanical Engineering at the POSTECH created metasurface display technology. This technology allows holograms to display multiple images based on the observer's viewing angle. The findings were recently published in Nano Letters, an international journal focusing on nanoscale research and applications.