Bound state in the continuum (BIC) is a mathematical concept with an infinite radiative quality factor (Q) that exists only in an ideal infinite array of resonators. In photonics, it is essential to ...achieve high Q resonances for enhanced light‐mater interactions that could enable low‐threshold lasers, ultrasensitive sensors, and optical tweezers. Hence, it is important to explore BICs in different photonic systems including subwavelength metamaterials where symmetry‐protected dual BICs exist. The spectral features of dual BICs are experimentally verified in the terahertz domain by breaking the C2 symmetry that invokes a leakage channel in the form of weakly radiating Fano resonance and electromagnetically induced transparency. The radiative Q factors tend to infinity at discrete symmetry‐restoring points and obey an inverse square dependence on the structural asymmetry. BICs in metamaterials allow extreme field confinement with small mode volumes, thereby improving the rate of spontaneous emission in the cavity with much larger Purcell factor. In addition, the topological nature enables a robust existence of BICs with a vector beam profile that is ideal for lasing. The symmetry‐protected BICs in metamaterials also possess a unique advantage of scalability at different wavelengths for potential applications in sensing, lasing, switching, and spectral filtering.
Dual bound states in the continuum (BICs) in planar metamaterials with symmetry‐protected polarization‐dependent features are experimentally demonstrated. The radiative Q factors show an inverse square dependence on the structural asymmetry and tend to infinity at perfect symmetry. Topological nature of BIC enables their robust existence with a vector beam profile that is ideal for lasing.
Next‐generation devices for low‐latency and seamless communication are envisioned to revolutionize information processing, which would directly impact human lives, technologies, and societies. The ...ever‐increasing demand for wireless data traffic can be fulfilled by the terahertz band, which has received tremendous attention as the final frontier of the radio spectrum. However, attenuation due to atmospheric humidity and free‐space path loss significantly limits terahertz signal propagation. High‐gain antennas with directional radiation and reconfigurable beam steering are indispensable for loss compensation and terahertz signal processing, which are associated with spatial and temporal dimensions, respectively. Here, experimental demonstration of a spatiotemporal dielectric metasurface for unidirectional propagation and ultrafast spatial beam steering of terahertz waves is shown. The spatial dimension of the metasurface provides a solution to eliminate backscattering of collimated unidirectional propagation of the terahertz wave with steerable directionality. Temporal modulation of the spatial optical properties enables ultrafast reconfigurable beam steering. Silicon‐based spatiotemporal devices amalgamate the rich physics of metasurfaces and technologies that are promising for overcoming the bottlenecks of future terahertz communication, such as high‐speed and secure wireless data transmission, beamforming and ultrafast data processing.
A spatiotemporal dielectric metasurface for unidirectional beam steering of terahertz radiation is experimentally demonstrated at an ultrafast timescale. Backscattering is eliminated under Kerker's condition, enabling highly directional terahertz beams. The optically tunable silicon‐based spatiotemporal metasurface holds promise for designing low‐loss, reconfigurable terahertz meta‐antennas for sixth‐generation wireless communication, ultrafast beam‐forming, and data processing.
Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of ...microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.
Toroidal dipole is a localized electromagnetic excitation that plays an important role in determining the fundamental properties of matter due to its unique potential to excite nearly nonradiating ...charge–current configuration. Toroidal dipoles are recently discovered in metamaterial systems where it is shown that these dipoles manifest as poloidal currents on the surface of a torus and are distinctly different from the traditional electric and magnetic dipoles. Here, an active toroidal metamaterial switch is demonstrated in which the toroidal dipole can be dynamically switched to the fundamental electric dipole or magnetic dipole, through selective inclusion of active elements in a hybrid metamolecule design. Active switching of nonradiating toroidal configuration into highly radiating electric and magnetic dipoles can have significant impact in controlling the electromagnetic excitations in free space and matter that can have potential applications in designing efficient lasers, sensors, filters, and modulators.
Toroidal dipole excitation can be dynamically switched to the fundamental electric dipole or magnetic dipole, through selective inclusion of the active elements in a mirrored configuration of Fano resonators. Optical switching between various multipole excitations that range from nonradiating to strongly radiating configuration presents an innovative approach to implement more than one electromagnetic feature in a single device.
Abstract
The revolutionary 5G cellular systems represent a breakthrough in the communication network design to provide a single platform for enabling enhanced broadband communications, virtual ...reality, autonomous driving, and the internet of everything. However, the ongoing massive deployment of 5G networks has unveiled inherent limitations that have stimulated the demand for innovative technologies with a vision toward 6G communications. Terahertz (0.1-10 THz) technology has been identified as a critical enabler for 6G communications with the prospect of massive capacity and connectivity. Nonetheless, existing terahertz on-chip communication devices suffer from crosstalk, scattering losses, limited data speed, and insufficient tunability. Here, we demonstrate a new class of phototunable, on-chip topological terahertz devices consisting of a broadband single-channel 160 Gbit/s communication link and a silicon Valley Photonic Crystal based demultiplexer. The optically controllable demultiplexing of two different carriers modulated signals without crosstalk is enabled by the topological protection and a critically coupled high-quality (
Q
) cavity. As a proof of concept, we demultiplexed high spectral efficiency 40 Gbit/s signals and demonstrated real-time streaming of uncompressed high-definition (HD) video (1.5 Gbit/s) using the topological photonic chip. Phototunable silicon topological photonics will augment complementary metal oxide semiconductor (CMOS) compatible terahertz technologies, vital for accelerating the development of futuristic 6G and 7G communication era driving the real-time terabits per second wireless connectivity for network sensing, holographic communication, and cognitive internet of everything.
The strikingly contrasting optical properties of various phases of chalcogenide phase change materials (PCM) has recently led to the development of novel photonic devices such as all‐optical non‐von ...Neumann memory, nanopixel displays, color rendering, and reconfigurable nanoplasmonics. However, the exploration of chalcogenide photonics is currently limited to optical and infrared frequencies. Here, a phase change material integrated terahertz metamaterial for multilevel nonvolatile resonance switching with spatial and temporal selectivity is demonstrated. By controlling the crystalline proportion of the PCM film, multilevel, non‐volatile, terahertz resonance switching states with long retention time at zero hold power are realized. Spatially selective reconfiguration at sub‐metamaterial scale is shown by delivering electrical stimulus locally through designer interconnect architecture. The PCM metamaterial also features ultrafast optical modulation of terahertz resonances with tunable switching speed based on the crystalline order of the PCM film. The multilevel nonvolatile, spatially selective, and temporally tunable PCM metamaterial will provide a pathway toward development of novel and disruptive terahertz technologies including spatio‐temporal terahertz modulators for high speed wireless communication, neuromorphic photonics, and machine‐learning metamaterials.
A chalcogenide phase‐change material, germanium antimony telluride, integrated with a terahertz metamaterial, shows multilevel nonvolatile resonance switching states, electrically controlled spatial terahertz modulation, and tunable ultrafast resonance modulation under optical stimulus. The unique properties of GST open up a new paradigm of multidimensional manipulation of terahertz waves across spectral, spatial and temporal domains.
A broad range of dynamic metasurfaces has been developed for manipulating the intensity, phase and wavefront of electromagnetic radiation from microwaves to optical frequencies. However, most of ...these metasurfaces operate in single-input-output state. Here, we experimentally demonstrate a reconfigurable MEMS Fano resonant metasurface possessing multiple-input-output (MIO) states that performs logic operations with two independently controlled electrical inputs and an optical readout at terahertz frequencies. The far-field behaviour of Fano resonance exhibits XOR and XNOR operations, while the near-field resonant confinement enables the NAND operation. The MIO configuration resembling hysteresis-type closed-loop behaviour is realized through inducing electromechanically tuneable out-of-plane anisotropy in the near-field coupling of constituent resonator structures. The XOR metamaterial gate possesses potential applications in cryptographically secured terahertz wireless communication networks. Furthermore, the MIO features could lay the foundation for the realization of programmable and randomly accessible metamaterials with enhanced electro-optical performance across terahertz, infrared and optical frequencies.
The realization of integrated, low-cost and efficient solutions for high-speed, on-chip communication requires terahertz-frequency waveguides and has great potential for information and communication ...technologies, including sixth-generation (6G) wireless communication, terahertz integrated circuits, and interconnects for intrachip and interchip communication. However, conventional approaches to terahertz waveguiding suffer from sensitivity to defects and sharp bends. Here, building on the topological phase of light, we experimentally demonstrate robust terahertz topological valley transport through several sharp bends on the all-silicon chip. The valley kink states are excellent information carriers owing to their robustness, single-mode propagation and linear dispersion. By leveraging such states, we demonstrate error-free communication through a highly twisted domain wall at an unprecedented data transfer rate (exceeding ten gigabits per second) that enables real-time transmission of uncompressed 4K high-definition video (that is, with a horizontal display resolution of approximately 4,000 pixels). Terahertz communication with topological devices opens a route towards terabit-per-second datalinks that could enable artificial intelligence and cloud-based technologies, including autonomous driving, healthcare, precision manufacturing and holographic communication.Robust terahertz wave transport is demonstrated on a silicon chip using the valley Hall topological phase. Error-free communication is achieved at a data rate of 11 Gbit s−1, enabling real-time transmission of uncompressed 4K high-definition video.
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