Diamond step-index nanowaveguide to structure light efficiently in near and deep ultraviolet regimes

Fluid-responsive tunable metasurfaces for high-fidelity optical wireless communication

Optical wireless communication (OWC), with its blazing data transfer speed and unparalleled security, is a futuristic technology for wireless connectivity. Despite the significant advancements in OWC, the realization of tunable devices for on-demand and versatile connectivity still needs to be explored. This presents a considerable limitation in utilizing adaptive technologies to improve signal directivity and optimize data transfer. This study proposes a unique platform that utilizes tunable, fluid-responsive multifunctional metasurfaces offering dynamic and unprecedented control over electromagnetic wave manipulation to enhance the performance of OWC networks. We have achieved real-time, on-demand beam steering with vary-focusing capability by integrating the fabricated metasurfaces with different isotropic fluids. Furthermore, the designed metasurfaces are capable of polarization-based switching of the diffracted light beams to enhance overall productivity. Our research has showcased the potential of fluid-responsive tunable metasurfaces in revolutionizing OWC networks by significantly improving transmission reliability and signal quality through real-time adjustments. The proposed methodology is verified by designing and fabricating an all-dielectric metasurface measuring 500 μm × 500 μm and experimentally investigating its fluid-responsive vary-focal capability. By incorporating fluid-responsive properties into spin-decoupled metasurfaces, we aim to develop advanced high-tech optical devices and systems to simplify beam-steering and improve performance, adaptability, and functionality, making the devices suitable for various practical applications.

Ultraviolet-Visible Multifunctional Vortex Metaplates by Breaking Conventional Rotational Symmetry

Metasurfaces have shown remarkable potential to manipulate many of light's intrinsic properties, such as phase, amplitude, and polarization. Recent advancements in nanofabrication technologies and persistent efforts from the research community result in the realization of highly efficient, broadband, and multifunctional metasurfaces. Simultaneous control of these characteristics in a single-layered metasurface will be an apparent technological extension. Here, we demonstrate a broadband multifunctional metasurface platform with the unprecedented ability to independently control the phase profile for two orthogonal polarization states of incident light over dual-wavelength spectra (ultraviolet to visible). In this work, multiple single-layered metasurfaces composed of bandgap-engineered silicon nitride nanoantennas are designed, fabricated, and optically characterized to demonstrate broadband multifunctional light manipulation ability, including structured beam generation and meta-interferometer implementation. We envision the presented metasurface platform opening new avenues for broadband multifunctional applications including ultraviolet-visible spectroscopy, spatially modulated illumination microscopy, optical data storage, and information encoding.

Anti-reflecting metasurface for broadband polarization independent absorption at Ku band frequencies

An impedance matched metasurface can efficiently channel the electromagnetic fields for maximum power transfer. The thin film based impedance matching techniques often utilize highly dissipative materials and destructive interference of reflection components from multiple subwavelength layers. Here, we propose a novel method to achieve anti reflection characteristics through destructive interference of antiparallel electromagnetic scattering emerging from chiral metasurface. The supercell structure of metasurface consists of four adjacent multi split-rings on FR-4 substrate. The split-rings are arranged to induce anti-parallel surface currents leading to destructive interference for scattered fields. The antireflection characteristics results in near perfect broadband absorption at dual frequency bands. A broadband absorption of 983 MHz is achieved between 12.687 and 13.669 GHz. Similarly, a narrow band absorption of 108 MHz is achieved in frequency range of 15.307–15.415 GHz. The impedance matched with unique symmetric design of supercell results in identical absorption for both x- and y-polarized incident fields. The numerical and experimental results verify broadband absorption characteristics at Ku band frequencies. The proposed metasurface absorber can be used for microwave energy harvesting applications.

Highly Efficient Perfect Vortex Beams Generation Based on All-Dielectric Metasurface for Ultraviolet Light

Featuring shorter wavelengths and high photon energy, ultraviolet (UV) light enables many exciting applications including photolithography, sensing, high-resolution imaging, and optical communication. The conventional methods of UV light manipulation through bulky optical components limit their integration in fast-growing on-chip systems. The advent of metasurfaces promised unprecedented control of electromagnetic waves from microwaves to visible spectrums. However, the availability of suitable and lossless dielectric material for the UV domain hindered the realization of highly efficient UV metasurfaces. Here, a bandgap-engineered silicon nitride (Si3N4) material is used as a best-suited candidate for all-dielectric highly efficient UV metasurfaces. To demonstrate the wavefront manipulation capability of the Si3N4 for the UV spectrum, we design and numerically simulate multiple all-dielectric metasurfaces for the perfect vortex beam generation by combing multiple phase profiles into a single device. For different numerical apertures (NA =0.3 and 0.7), it is concluded that the diffracted light from the metasurfaces with different topological charges results in an annular intensity profile with the same ring radius. It is believed that the presented Si3N4 materials and proposed design methodology for PV beam-generating metasurfaces will be applicable in various integrated optical and nanophotonic applications such as information processing, high-resolution spectroscopy, and on-chip optical communication.

Enhancement of efficiency on the Pancharatnam-Berry geometric phase metalens in the terahertz region

Traditional terahertz lenses face high thickness, low transmittance, difficult processing, and other problems that are not conducive to mass production and integration. Here, we propose a wideband all-dielectric Pancharatnam-Berry geometric phase cell structure to construct a metasurface flat lens. However, when the geometrical phase element structure rotates, the transmission efficiency of the periodic element structure obviously decreases, which will lead to the decrease of the efficiency of the designed flat lens. In order to improve the efficiency, we propose to add a layer of tapered microstructure on the flat substrate to greatly improve the transmission efficiency of the element structure, thus leading to the improvement of the efficiency of the metasurface lens. By comparing the metasurface lens with conical and planar substrates, the metasurfaces with conical structure can greatly improve the transmission efficiency at broadband and wide angle ranges.

High-efficiency transmissive invisibility cloaking based on all-dielectric multilayer frame structure metasurfaces

Metasurfaces provide a completely new path to realize the cloaking effect due to their excellent electromagnetic wavefront manipulation. However, most previous metasurfaces realized cloaking by using phase compensation, which is limited by the reflection phase formula and can be used only for reflection mode. We use the generalized Snell's law to propose a free-space transmission stealth device, consisting of multilayer all-dielectric metasurfaces. We utilize three phase gradient all-dielectric silicon metasurfaces that, respectively, play the role of beam splitting, steering, and collection to guide incident waves around the object, thereby forming an ideal stealth area in free space. All-dielectric metasurfaces can greatly reduce transmission loss and enhance efficiency to a large extent. The advantage of choosing an all-dielectric material is that it is easy to process and more suitable in practice. Simulation results of the near field and far field prove that this cloak has a cloaking effect at 1 THz. Our work opens up a new path for transmissive stealth.