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Metasurface analogues of electromagnetically induced transparency (EIT) have been a focus of the nanophotonics field in recent years, due to their ability to produce high-quality factor (Q-factor) resonances. Such resonances are expected to be useful for applications such as low-loss slow-light devices and highly sensitive optical sensors. However, ohmic losses limit the achievable Q-factors in conventional plasmonic EIT metasurfaces to values <~10, significantly hampering device performance. Here we experimentally demonstrate a classical analogue of EIT using all-dielectric silicon-based metasurfaces. Due to extremely low absorption loss and coherent interaction of neighbouring meta-atoms, a Q-factor of 483 is observed, leading to a refractive index sensor with a figure-of-merit of 103. Furthermore, we show that the dielectric metasurfaces can be engineered to confine the optical field in either the silicon resonator or the environment, allowing one to tailor light–matter interaction at the nanoscale. Electromagnetically induced transparency—an effect in atomic physics caused by interference between transitions—has found analogues in other areas, like nanophotonics. Yang et al . exploit this effect in an all-dielectric metasurface to produce high-Q-factor resonances ideal for refractive index sensing.

This paper documents a simple parametric polynomial line-of-sight channel model for 100–450 GHz band. The band comprises two popular beyond fifth generation (B5G) frequency bands, namely, the D band (110–170 GHz) and the low-THz band (around 275–325 GHz). The main focus herein is to derive a simple, compact, and accurate molecular absorption loss model for the 100–450 GHz band. The derived model relies on simple absorption line shape functions that are fitted to the actual response given by complex but exact database approach. The model is also reducible for particular sub-bands within the full range of 100–450 GHz, further simplifying the absorption loss estimate. The proposed model is shown to be very accurate by benchmarking it against the exact response and the similar models given by International Telecommunication Union Radio Communication Sector. The loss is shown to be within ±2 dBs from the exact response for one kilometer link in highly humid environment. Therefore, its accuracy is even much better in the case of usually considered shorter range future B5G wireless systems.

Plasmonic control: enter the spaser Nanoplasmonics — the nanoscale manipulation of surface plasmons (fluctuations in the electron density at a metallic surface) — could revolutionize applications ranging from sensing and biomedicine to imaging and information technology. But first, we need a simple and efficient method for actively generating coherent plasmonic fields. This is in theory possible with the spaser, first proposed in 2003 as a device that generates and amplifies surface plasmons in the same way that a laser generates and amplifies photons. Now Noginov et al . present the first unambiguous experimental demonstration of spasing, using 44-nm diameter nanoparticles with a gold core and dye-doped silica shell. The system generates stimulated emission of surface plasmons in the same way as a laser generates stimulated emission of coherent photons, and has been used to implement the smallest nanolaser reported to date, and the first operating at visible wavelengths. Nanoplasmonics promises to revolutionize applications ranging from sensing and biomedicine to imaging and information technology, but its full development is hindered by the lack of devices that can generate coherent plasmonic fields. In theory, this is possible with a so-called 'spaser' — analogous to a laser — which would generate stimulated emission of surface plasmons. This is now realized experimentally, and should enable many new technological developments. One of the most rapidly growing areas of physics and nanotechnology focuses on plasmonic effects on the nanometre scale, with possible applications ranging from sensing and biomedicine to imaging and information technology 1 , 2 . However, the full development of nanoplasmonics is hindered by the lack of devices that can generate coherent plasmonic fields. It has been proposed 3 that in the same way as a laser generates stimulated emission of coherent photons, a ‘spaser’ could generate stimulated emission of surface plasmons (oscillations of free electrons in metallic nanostructures) in resonating metallic nanostructures adjacent to a gain medium. But attempts to realize a spaser face the challenge of absorption loss in metal, which is particularly strong at optical frequencies. The suggestion 4 , 5 , 6 to compensate loss by optical gain in localized and propagating surface plasmons has been implemented recently 7 , 8 , 9 , 10 and even allowed the amplification of propagating surface plasmons in open paths 11 . Still, these experiments and the reported enhancement of the stimulated emission of dye molecules in the presence of metallic nanoparticles 12 , 13 , 14 lack the feedback mechanism present in a spaser. Here we show that 44-nm-diameter nanoparticles with a gold core and dye-doped silica shell allow us to completely overcome the loss of localized surface plasmons by gain and realize a spaser. And in accord with the notion that only surface plasmon resonances are capable of squeezing optical frequency oscillations into a nanoscopic cavity to enable a true nanolaser 15 , 16 , 17 , 18 , we show that outcoupling of surface plasmon oscillations to photonic modes at a wavelength of 531 nm makes our system the smallest nanolaser reported to date—and to our knowledge the first operating at visible wavelengths. We anticipate that now it has been realized experimentally, the spaser will advance our fundamental understanding of nanoplasmonics and the development of practical applications.

Organic semiconductors are commonly used as charge-extraction layers in metal-halide perovskite solar cells. However, parasitic light absorption in the sun-facing front molecular layer, through which sun light must propagate before reaching the perovskite layer, may lower the power conversion efficiency of such devices. Here, we show that such losses may be eliminated through efficient excitation energy transfer from a photoexcited polymer layer to the underlying perovskite. Experimentally observed energy transfer between a range of different polymer films and a methylammonium lead iodide perovskite layer was used as basis for modelling the efficacy of the mechanism as a function of layer thickness, photoluminescence quantum efficiency and absorption coefficient of the organic polymer film. Our findings reveal that efficient energy transfer can be achieved for thin (≤10 nm) organic charge-extraction layers exhibiting high photoluminescence quantum efficiency. We further explore how the morphology of such thin polymer layers may be affected by interface formation with the perovskite. The performance of perovskite solar cells can be limited by light absorption loss in organic charge extraction layers, through which sun light must propagate before reaching the perovskite. Here, the authors demonstrate that efficient energy transfer to the perovskite layer from a thin organic layer is able to eliminate this parasitic loss.

The development of a miniaturised device that provides efficient beam manipulation with high transmittance is extremely desirable for the broad range of applications including holography, metalens, and imaging. Recently, the potential of dielectric metasurfaces has been unleashed to efficiently manipulate the beam with full 2π-phase control by overlapping the electric and magnetic dipole resonances. However, in the visible range for available materials, it comes with the price of higher absorption that reduces efficiency. Here, we have considered dielectric amorphous silicon (a-Si) nanodisk and engineered them in such a way which provides minimal absorption loss in the visible range. We have experimentally demonstrated meta-deflector with high transmittance which operates in the visible wavelengths. The supercell of proposed meta-deflector consists of 15 amorphous silicon nanodisks numerically shows the transmission efficiency of 95% and deflection efficiency of 95% at operating wavelength of 715 nm. However, experimentally measured transmission and deflection efficiencies are 83% and 71%, respectively, having the experimental deflection angle of 8.40°. Nevertheless, by reducing the supercell length, the deflection angle can be controlled, and the value 15.50° was experimentally achieved using eight disks supercell. Our results suggest a new way to realise the highly transmittance metadevice with full 2π-phase control operating with the visible light which could be applicable in the imaging, metalens, holography, and display applications.

With many potential applications in mind, great effort is being applied to develop a terahertz-wave technology platform on which waves can be manipulated with sufficient confinement and efficient interaction for the development of smart components. Here, we utilize the in-plane resonance of a thin, planar photonic-crystal slab with negligible absorption loss to successfully demonstrate and visualize terahertz-wave trapping. We artificially introduce free carriers, which interact with the trapped waves, and capture them in the slab by absorption. Our system exhibits an experimental absorptivity (interaction efficiency) of ∼99% and a broad bandwidth (absorptivity of ≥90%) that covers 17% of the centre frequency. We also demonstrate its application to the stabilization of terahertz wireless communication systems. Our study shows the capability of photonic crystals as a terahertz-wave platform, the application of which may be extended to other components including filters, couplers, antennas, detectors, modulators, switches and emitters. Trapping of a terahertz wave in a photonic-crystal slab and subsequent ‘capture’ through absorption are demonstrated. Over 90% of the wave lying within 17% of the centre frequency is absorbed. Application to the stabilization of terahertz wireless communication systems is shown.

Optical fiber has become an indispensable tool in our everyday life because of it’s special properties to send light to long distances without losing much of it’s signal power, compared to conventional wire. Although optical fiber is proven to be more efficient and very fast in delivering signal in the area of communication industry, still some losses of signals occur inside the fiber optic cable. Most of the losses have been described in standard text books viz. scattering loss, bending losses, absorption loss etc are pretty straight forward when one calculates the loss of signal power inside an optical fiber. In this article, the loss of signal is calculated and studied by considering Fresnel’s equation (due to Fresnel’s reflection at the boundary) along with absorption loss due to materials property. Although Fresnel’s loss is very small but it could be significant if the fiber connection is thousands of kilometers long and there are multiple joints of different fibers. This Fresnel’s loss only happens at the boundary of a material. For simplicity the loss due to scattering, bending of rays and any other types of losses have been ignore in this work, except absorption loss.

Quantum dot enhancement film (QDEF) working in tandem with a blue light-emitting-diode (LED) back-light-unit (BLU) has been recently used in liquid crystal display (LCD) to minimize the cross talks between the polarized emitting B-, G-, and R-light. However, they still exhibit a fundamental and considerable emitting-light-power loss from QDEF because of the light absorption loss in resin and transparent films of QDEF. In this work, we propose and demonstrate the superiority of the LCD using blue-(B-), green-(G-), and red-(R-) perovskite-quantum-dot (PrQD) functional CFs coupled with a blue LED BLU. This LCD using PrQD functional CFs and a blue LED BLU features cross-talk free spectra of polarized emitting B-, G-, and R-light, maximizing the LCD color gamut and exhibiting a world record performance of over 102.7% (137%) of Rec.2020 standard (NTSC standard). Theoretically, such an improvement in color gamut would facilitate unlimited scaling-down of the pixel leading to super ultra-high resolution LCD.

The investigation on metalenses have been rapidly developing, aiming to bring compact optical devices with superior properties to the market. Realizing miniature optics at the UV frequency range in particular has been challenging as the available transparent materials have limited range of dielectric constants. In this work we introduce a low absorption loss and low refractive index dielectric material magnesium oxide, MgO, as an ideal candidate for metalenses operating at UV frequencies. We theoretically investigate metalens designs capable of efficient focusing over a broad UV frequency range (200–400 nm). The presented metalenses are composed of sub-wavelength MgO nanoblocks, and characterized according to the geometric Pancharatnam–Berry phase method using FDTD method. The presented broadband metalenses can focus the incident UV light on tight focal spots (182 nm) with high numerical aperture ( NA ≈ 0.8 ). The polarization conversion efficiency of the metalens unit cell and focusing efficiency of the total metalens are calculated to be as high as 94%, the best value reported in UV range so far. In addition, the metalens unit cell can be hybridized to enable lensing at multiple polarization states. The presented highly efficient MgO metalenses can play a vital role in the development of UV nanophotonic systems and could pave the way towards the world of miniaturization.

The excrescent electromagnetic (EM) radiation exposure in the air threatens human health and electronic equipment due to the abuse of EM waves in wireless telecommunication technology and electronic applications. Consequently, electromagnetic interference (EMI) shielding materials are provided to solve the EM waves pollution problem. In particular, the appearance of one-dimensional (1D) metallic, magnetic, and dielectric nanofillers will extremely reduce the density of EMI composite and enhance EMI protection performance because they can easily assemble to form complete two-dimensional (2D) or three-dimensional (3D) EMI network based on their high aspect ratio, large specific surface area, and additional attenuated sites. This review focuses on the EMI shielding composites with 1D metallic, magnetic, and dielectric nanofillers, which could be constructed in the final form of membrane- or aerogel/sponge-like shielding materials. According to the structural features, 1D metallic, magnetic, and dielectric nanofillers are classified into nanowires, nanorods, nanospindles, nanochains, nanofibers, nanotubes, nanorings, nanocoils, and quasi-one-dimensional (1D) van der Waals materials. Accordingly, the fabricated routes, shielding performances, and EM waves attenuation mechanism of the 1D metallic, magnetic, and dielectric nanofiller-based composites are summarized. It is found that the dominant shielding mechanism of most of the 1D metal-based EMI composites is reflection loss, while that of 1D magnetic and dielectric nanomaterials-based EMI composites is absorption loss caused by interfacial polarization, natural resonance, eddy current, and multiple scattering. Finally, the challenges and prospects of 1D nanofiller-based composites with a tunable architecture and composition are put forward, aiming to give a guideline for the next generation of high-performance EMI shielding materials.