Optimizing Motheye Nanostructures and Achieving 100% Transmission

Nano-scaled metallic or dielectric structures may provide various ways to trap light into thin-film solar cells for improving the conversion efficiency. In most schemes, the textured active layers are involved into light trapping structures that can provide perfect optical benefits but also bring undesirable degradation of electrical performance. Here we propose a novel approach to design high-performance thin-film solar cells. In our strategy, a flat active layer is adopted for avoiding electrical degradation, and an optimization algorithm is applied to seek for an optimized light trapping structure for the best optical benefit. As an example, we show that the efficiency of a flat a-Si:H thin-film solar cell can be promoted close to the certified highest value. It is also pointed out that, by choosing appropriate dielectric materials with high refractive index (>3) and high transmissivity in wavelength region of 350 nm–800 nm, the conversion efficiency of solar cells can be further enhanced.

In this article, we propose a new paradigm to design frequency-selective rasorber (FSR) with two-sided efficient absorptions and broadband transmission in a chiral structure. The proposed FSR is implemented via combining two chiral absorber layers with a bandpass frequency-selective surface (FSS). An absorptive split-ring resonator (ASRR) inserted with a resistive film is designed to provide efficient spin-sensitive absorption. Then, four ASRRs are arranged to form a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{4}$ </tex-math></inline-formula> symmetric split-ring absorber (SRA) with identical absorption for distinct polarized incident waves. The physical mechanisms of spin-selective absorption and polarization-insensitive absorption are discussed theoretically. The broadband bandpass FSS is introduced to provide a transparent window and ground plane for the absorbers. A prototype is fabricated and measured to verify the feasibility of the method. The simulation and experimental results manifest over 90% absorptive bands of 1.5–3.6 and 15.2–21.6 GHz and a transmission band of 8–12 GHz with insertion loss less than 2 dB. Compared with previous FSRs, the proposed FSR has a broadband transmission, efficient absorptions with high-frequency selectivity, and easy geometric structure.

The efficient control of light propagation and localization at subwavelength scales enabled by nanophotonics has led to tremendous advances in tailoring light/matter interaction. Traditionally, this nanophotonic enhancement has been associated with the plasmonic resonances in metallic nanostructures. All-dielectric nanophotonic approaches have been introduced to overcome the innate losses of plasmonic geometries by leveraging high refractive index nanostructures that can be engineered to provide both electric and magnetic Mie resonances [1] . Nevertheless, such structures are still affected by radiative loss, decreasing the achievable resonance line sharpness and therefore putting an upper limit on the resonance quality factor. Recently, metasurfaces incorporating the physics of photonic bound states in the continuum (BICs) have emerged as a breakthrough toolkit for reducing these losses [2] , enabling all-dielectric nanophotonics with ultrasharp resonances and enabling a wide range of applications from optical phase control [3] to sensing [4] , [5] . The two headline geometries for realizing BIC resonances have been two-dimensional (2D) linear arrays of resonators with broken in-plane symmetry, which allows for precise control over the Q-factor [6] , as well as single-element resonators, where BICs emerge in a carefully tailored regime of interfering Mie modes [7] .

We report a numerically obtained design of a hollow-core plastic microstructured optical fiber (HC-pMOF) for efficient high power terahertz (THz) transmission. The effects of fiber's structural parameters on the propagating THz pulse are carried out in detail. The cross-section of HC-pMOF is composed of hexagonally arranged three periodic cladding rings made of air holes embedded in a uniform Teflon matrix. The THz guidance through the central hollow-core is achieved through photonic band-gap (PBG) effect of the periodic cladding structure. The effects of cladding periodicity as well as core size are investigated for broad-band, low-loss and low-dispersive THz wave transmission and the estimated low-loss ( 450 GHz. Furthermore, we have investigated the effect of introducing a chirp in the air-hole sizes of the periodic cladding.

We propose a hollow core Bragg fiber (HC-BF) with a heterostructured cladding based on the ternary 1-D photonic crystal (T-1DPC) in this paper. The distinguishing ternary unit cell of T-1DPC is formed from a polyetherimide (PEI) layer sandwiched by two As2Se3 layers of the same thickness. We demonstrate its capability for mid-infrared broadband and low-loss transmission by numerically simulating and analyzing the omnidirectional photonic bandgap (OPBG) and the modal loss characteristics. The results show that the T-1DPC-based heterostructured cladding can effectively broaden the OPBG, which is only due to the blue-shift of the lower bandgap edge wavelength. Compared with that for the binary-1DPC-based HC-BF, the transmission loss for the T-1DPC-based HC-BF can be reduced by three orders of magnitude over most of the OPBG range. The large loss contrast is essentially attributed to the enhancement of the multilayer reflection from the T-1DPC-based cladding. Most notably, for a T-1DPC-based cladding with three groups, the transmission band with loss lower than 0.01 dB/m for the HE11 mode can cover almost the whole 3 to 5 μm range, with the exception of several loss peaks near the short-wavelength edge. Even with the cladding material absorption included, the transmission loss for the HE11 mode in the T-1DPC-based HC-BF can be still lower than 0.1 dB/m over the whole OPBG range.

Efficient antireflective downconversion Er3+ doped ZnO/Si thin film

The analysis of diffracted light from periodic structures is shown to be a versatile metrology technique applicable to inline metrology for periodic nanostructures. We show that 10 nm changes in periodic structures can be traced optically by means of sub-wavelength diffraction. Polymer gratings were fabricated by electron beam lithography. The gratings have a common periodicity of 6 μm, but different line width, ranging from 370 to 550 nm in 10 nm steps. A comparison between the resulting diffraction patterns shows marked differences in intensity which are used to sense nanometre scale deviations in periodic structures.

We report on the effect of femtosecond-laser-induced periodic surface structures (LIPSS) on the tribological properties of stainless steel. Uniform periodic nanostructures were produced on AISI 304L (American Iron and Steel Institute steel grade) steel surfaces using an 800-nm femtosecond laser. The spatial periods of LIPSS measured by field emission scanning electron microscopy ranged from 530 to 570 nm. The tribological properties of smooth and textured surfaces with periodic nanostructures were investigated using reciprocating ball-on-flat tests against AISI 440C balls under both dry and starved oil lubricated conditions. The friction coefficient of LIPSS covered surfaces has shown a lower value than that of the smooth surface. The induced periodic nanostructures demonstrated marked potential for reducing the friction coefficient compared with the smooth surface.

Engineered materials, such as new composites and electromagnetic bandgap and periodic structures have been of strong interest in recent years, due to their extraordinary and unique electromagnetic behaviors. This paper discusses how modified materials, inductive/capacitive lumped loads, and magnetic materials/crystals are impacting antenna miniaturization and performance improvements (e.g., bandwidth and gain reduction, multi-functionality, etc.). Dielectric design and texturing for impedance matching has led to significant size reduction and higher-bandwidth low-frequency antennas, for example. The recently introduced magnetic-photonic crystals (MPCs) and double band-edge (DBE) materials, displaying spectral nonreciprocity, are also discussed. Studies of these crystals demonstrated that magnetic-photonic crystals exhibit the interesting phenomena of (a) drastic slowing down of the incoming wave, coupled with (b) significant amplitude growth, while (c) maintaining minimal reflection at the interface with free space. The phenomena are associated with diverging frozen modes that occur around the stationary inflection points within the band diagram. Taking advantage of the frozen-mode phenomena, we demonstrate that individual antenna elements and linear or volumetric arrays embedded within the magnetic-photonic crystal and double band-edge structures allow for antenna sensitivity and gain enhancements

Although titanium (Ti) is a common biomaterial, controlling cell spreading by forming periodic structures using a femtosecond laser should improve its biocompatibility. Herein we investigate the influence of periodic nanostructures formed on the surface of a Ti plate on cell spreading. Nanostructures with a periodicity of 590 nm are formed using a femtosecond laser with a wavelength of 775 nm. Cell spreading on the plate without period structures lacks a definite direction, whereas cell spreading on the Ti plate with periodic structures occurs along the grooves, suggesting that forming periodic structures via a femtosecond laser can control cell spreading.

Crystal cleavage, periodic nanostructure and surface modification of SiC ablated by femtosecond laser in different media

Periodic nanostructures have been widely used on emerging nano-products such as plasmonic solar cell and nano-optics. However, lack of cost-effective fabrication techniques has become the bottleneck for commercialization of these nano-products. In this work, we develop a scale up approach to fabricate high-precision nanostructures in large area. In this method, a nano-scale single crystal diamond (SCD) tool is produced by focused ion beam (FIB) machining. The nano SCD tool is then further applied to cut periodic nanostructures using single-point diamond turning (SPDT). A divergence compensation method and surface topography generation model forms a deterministic FIB fabrication approach. It has been used to generate four periods of the required periodic nano-grating structures (with a minimal dimension of 150 nm) on a normal SCD tool tip and achieves 10 nm form accuracy. The contribution of the beam tail effect has also been evaluated by using the surface topography simulation method. The fabricated diamond tool is then applied to obtain nano-grating on an electroless nickel substrate in a total area of 5 × 2 mm2 through SPDT. The whole SPDT machine process only takes 2 min (with a material removal rate up to 1.8 × 104 μm3 s−1). Due to the elastic recovery that occurred upon the workpiece material, the practical cutting width is 13 nm smaller than the tool tip. The machining trial shows it is very promising to apply this scale up nanofabrication approach for commercialization of nano-products which possess period nanostructures.

Remarkable physical properties of two-dimensional (2D) materials provide significant potential for novel photonic devices, many of which rely on nonlinear optical effects in these 2D materials. Here we use a theoretical and computational approach we have recently introduced to describe the linear and nonlinear optical physics of nanostructured 2D materials embedded in periodic structures containing regular three-dimensional (3D) optical media, such as diffraction gratings and metamaterials. Thus, we use the proposed method to demonstrate enhanced nonlinear optical interactions in periodic photonic nanostructures via resonant excitation of phase-matched waveguide modes, enhanced nonlinearity of nanostructures containing graphene and other 2D nanomaterials, and Fano resonances for increasing the efficiency of 2D-3D heteromaterials.

We consider a Fabry-Perot resonance (a transmission band edge resonance) in periodic layered structures involving birefringent layers. In a previous publication [Phys. Rev. E 72, 036619 (2005)] we have shown that the presence of birefringent layers with misaligned in-plane anisotropy can dramatically enhance the performance of the photonic-crystal resonator. It allows us to reduce its size by an order of magnitude without compromising on its performance. The key characteristic of the enhanced slow-wave resonator is that the Bloch dispersion relation $\ensuremath{\omega}(k)$ of the periodic structure displays a degenerate photonic band edge, in the vicinity of which the dispersion curve can be approximated as $\mathrm{\ensuremath{\Delta}}\ensuremath{\omega}\ensuremath{\sim}(\mathrm{\ensuremath{\Delta}}k{)}^{4}$, rather than $\mathrm{\ensuremath{\Delta}}\ensuremath{\omega}\ensuremath{\sim}(\mathrm{\ensuremath{\Delta}}k{)}^{2}$. Such a situation can be realized in specially arranged stacks of misaligned anisotropic layers. On the down side, the presence of birefringent layers results in the slow-wave resonance being coupled only with one (elliptic) polarization component of the incident wave, while the other polarization component is reflected back to space. In this paper we show how a small modification of the periodic layered array can solve the above fundamental problem and provide a perfect impedance match regardless of the incident wave polarization, while preserving the giant slow-wave resonance characteristic of a degenerate photonic band edge. Both features are of critical importance for many practical applications, such as the enhancement of various light-matter interactions, light amplification and lasing, optical and microwave filters, antennas, etc.

The extended tanh method for the Zakharov–Kuznetsov (ZK) equation, the modified ZK equation, and its generalized forms