Nanowire Gratings Research Articles

A linearly polarized white light based on a composite metal-dielectric-metal nanowire grating

A linearly polarized white light based on a composite metal-dielectric-metal nanowire grating

Deep Learning‐Assisted Design of Bilayer Nanowire Gratings for High‐Performance MWIR Polarizers

AbstractOptical metamaterials have revolutionized imaging capabilities by manipulating light‐matter interactions at the nanoscale beyond the diffraction limit. Bilayer nanowire grating configurations exhibit significant potential as exceptional elements for high‐performance polarimetric imaging systems. However, conventional computational approaches for predicting electromagnetic responses are time‐consuming and labor‐intensive, and thereby, the practical implementation remains challenging through an iterative design, analysis, and fabrication process. Here, a deep learning‐based design process is presented utilizing an artificial neural network (ANN) trained on finite element method (FEM) simulations that enables the prediction of bilayer nanowire gratings‐based electromagnetic responses. The study validates predictions through nanoimprinted bilayer nanowire gratings, demonstrating the reliability of the ANN's predictions. Furthermore, the research identifies critical geometric parameters significantly influencing transverse magnetic (TM) and transverse electric (TE) transmission. The ANN model effectively tailors design for specific mid‐wavelength infrared (MWIR) wavelengths, which may provide a practical tool for rapidly designing and optimizing metamaterial for high‐performance polarizers.

A linearly polarized light emission with a composite nanowire grating in whole white band

To obtain a highly linearly polarized light, a composite model consisting of white light emission, anti-reflection film, and metal-dielectric-metal nanowire grating was designed, analyzed, optimized, and fabricated. Based on the finite-difference time-domain method, the impacts of material, period, height, and incidence angle on the polarization performance of the composite model were discussed. The metal-dielectric-metal nanowire grating was fabricated on blue chip and fluorescent ceramics using nanoimprint technology. The employed materials of metal-dielectric-metal nanowire grating were aluminum and PMMA, with the period of 200 nm, wire width of 100 nm, and the height of metal and dielectric were 100 nm and 120 nm. Additionally, the anti-reflection film consisting of PMMA with the thickness of 45 nm was incorporated on fluorescent ceramics to enhance energy efficiency. Finally, through a series of test experiments, the composite model can be realized by the extinction ratio of 40 dB, while the transmittance of TM mode exceeds 50% at 450–750 nm. The theoretical analysis of this study is verified by experiments, and it has significant potential in the pursuit of high brightness, ultra-thin micro displays.

Polarization control of visible light based on composited multivariable nanowire gratings structure

Polarization control of visible light based on composited multivariable nanowire gratings structure

Chiral Excitation of Exchange Spin Waves Using Gold Nanowire Grating

We propose an experimental method for the unidirectional excitation of spin waves. By structuring Au nanowire arrays within a coplanar waveguide onto a thin yttrium iron garnet (YIG) film, we observe a chiral coupling between the excitation field geometry of the nanowire grating and several well-resolved propagating magnon modes. We report a propagating spin wave spectroscopy study with unprecedented spectral definition, wavelengths down to 130 nm and attenuation lengths well above 100 μm over the 20 GHz frequency band. The proposed experiment paves the way for future non-reciprocal magnonic devices.

Study of the Photoluminescence Enhancement Observed in ZnO Nanowire Gratings Optimally Grown by the Hydrothermal Method

AbstractAn original ZnO nanowire (NW) architecture has been developed, entirely based on a soft chemistry approach, and thoroughly assessed through optical measurements and electromagnetic simulations. This architecture relies on the photoimprinting of a sol–gel ZnO‐based photosensitive seed layer combined with the subsequent localized hydrothermal growth of ZnO NWs. The optimization of the elaboration protocol has been shown to lead to uniform and reproducible linear and periodic gratings of ZnO NWs with a width/pitch of 2/4 µm. The NW gratings are compared with full‐covered samples (NWs coating) elaborated from a nonimprinted seed layer. A morphological study reveals that NW gratings present a peculiar hedgehog‐like profile. Standard and angle‐resolved photoluminescence studies demonstrate that the ZnO NWs visible emission is strongly modified by the presence of NW gratings and that its red part is directionally extracted and enhanced by a factor of up to 2. The electromagnetic simulations performed for both samples highlight the role of the gratings acting as coupled microcavities that boost the ZnO emission through light localization and diffractive mechanisms. It enables the extraction of the resonant photons at specific angles and wavelengths.

Three-Dimensional Printing of Structural Color Using a Femtoliter Meniscus.

Structural colors are produced by the diffraction of light from microstructures. The collective arrangement of substructures is a simple and cost-effective approach for structural coloration represented by colloidal self-assembly. Nanofabrication methods enable precise and flexible coloration by processing individual nanostructures, but these methods are expensive or complex. Direct integration of desired structural coloration remains difficult because of the limited resolution, material-specificity, or complexity. Here, we demonstrate three-dimensional printing of structural colors by direct writing of nanowire gratings using a femtoliter meniscus of polymer ink. This method combines a simple process, desired coloration, and direct integration at a low cost. Precise and flexible coloration is demonstrated by printing the desired structural colors and shapes. In addition, alignment-resolved selective reflection is shown for displayed image control and color synthesis. The direct integration facilitates structural coloration on various substrates, including quartz, silicon, platinum, gold, and flexible polymer films. We expect that our contribution can expand the utility of diffraction gratings across various disciplines such as surface-integrated strain sensors, transparent reflective displays, fiber-integrated spectrometers, anticounterfeiting, biological assays, and environmental sensors.

Tunable Damping in Magnetic Nanowires Induced by Chiral Pumping of Spin Waves.

Spin-current and spin-wave-based devices have been considered as promising candidates for next-generation information transport and processing and wave-based computing technologies with low-power consumption. Spin pumping has attracted tremendous attention and has led to interesting phenomena, including the line width broadening, which indicates damping enhancement due to energy dissipation. Recently, chiral spin pumping of spin waves has been experimentally realized and theoretically studied in magnetic nanostructures. Here, we experimentally observe by Brillouin light scattering (BLS) microscopy the line width broadening sensitive to magnetization configuration in a hybrid metal-insulator nanostructure consisting of a Co nanowire grating dipolarly coupled to a planar continuous YIG film, consistent with the results of the measured hysteresis loop. Tunable line width broadening has been confirmed independently by propagating spin-wave spectroscopy, where unidirectional spin waves are detected. Position-dependent BLS measurement unravels an oscillating-like behavior of magnon populations in Co nanowire grating, which might result from the magnon trap effect. These results are thus attractive for reconfigurable nanomagnonics devices.

Further improvement of the light efficiency of LCDs via the asymmetric reflection of metallic nanowire gratings

Metallic nanowire gratings have been proposed for use as transmitted-type non-absorptive colorfilters and polarizers that take the place of the conventional absorptive ones in liquid crystal displays (LCDs), which can improve the light efficiency by recycling the reflected lights. To achieve a high recycling rate, the designed reflected light should be as high as possible, meaning absorption should be as low as possible. In this work, we find that higher reflection and lower loss can be obtained for the light incident to the grating side than to the substrate side in bi-layered aluminum nanowire gratings (BANGs), by decreasing light localization and waveguiding loss in the substrate. Taking full advantage of the reflection characteristics, we firstly demonstrate that when a BANG-based integrated polarizer and colorfilter is placed with its grating side facing the backlight in LCDs, more than a 30% light enhancement is obtained than the case with the substrate side facing the backlight. This work affords an essential guide for the design of eco-displays by using MNGs.

Linewidth study of pixelated aluminum nanowire gratings on polarization performance.

Nowadays, nanowire gratings are widely used in various applications such as imaging sensors and high-resolution microscopes. Structure parameters are the main factors that affect the optical performance of the gratings. This work aims to present the influence of the linewidth of pixelated aluminum nanowire gratings with a fixed period on the transmittance and extinction ratio in the visible region. By controlling the exposure doses of electron beam lithography (EBL), different linewidths of pixelated aluminum nanowire gratings with a period of 170 nm were fabricated. The significant effects of linewidth difference on the polarization performance were verified by the simulations of finite-difference time-domain (FDTD) software. The simulations were divided into two parts: the discussion of the pure aluminum without considering oxidation and the discussion of the surface aluminum being oxidized into the aluminum oxide. An optical system was built to evaluate the performance of the fabricated structures. The results show that the trends of the measurement results are consistent with that of simulation. This work will give a guide to the fabrication and evaluation of the nanowire gratings.

Control of plasmons excitation by P- and S-polarized light in gold nanowire gratings by azimuthal angle variation

Control of plasmons excitation by P- and S-polarized light in gold nanowire gratings by azimuthal angle variation

Resonant, broadband, and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths

Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximately 500 MW/cm2 peak power density, we predict third harmonic conversion efficiencies of approximately 1% in a silicon nanowire array, at nearly any desired UV or visible wavelength, including the range of negative dielectric constant. We also predict surface second harmonic conversion efficiencies of order 0.01%, depending on the electronic effective mass, bistable behavior of the signals as a result of a reshaped resonance, and the onset fifth order nonlinear effects. These remarkable findings, arising from the combined effects of nonlinear resonance dispersion, field localization, and phase-locking, could significantly extend the operational spectral bandwidth of silicon photonics, and strongly suggest that neither linear absorption nor skin depth should be motivating factors to exclude either semiconductors or metals from the list of useful or practical nonlinear materials in any spectral range.

Chiral excitation of spin waves in ferromagnetic films by magnetic nanowire gratings

We theoretically investigate the interlayer dipolar and exchange couplings for an array of metallic magnetic nanowires grown on top of an extended ultrathin yttrium iron garnet film. The calculated interlayer dipolar coupling agrees with observed anticrossings [Chen \emph{et al.}, Phys. Rev. Lett. \textbf{120}, 217202 (2018)], concluding that the interlayer exchange coupling is suppressed by a spacer layer between the nanowires and film. The Kittel mode in the nanowire array couples chirally to spin waves in the film, even though Damon-Eshbach surface modes do not exist. The chirality is suppressed when the interlayer exchange coupling becomes strong.

Shaping and polarizing fluorescence emission of a polycrystalline organic semiconductor film by plasmonic nanogratings

The fluorescence emission properties of hybrid systems consisting of a one-dimensional gold nanowire grating and an evaporated thin film of the small molecule organic semiconductor diindenoperylene (DIP) are investigated. The optical properties of the metallic systems are dominated by their plasmonic resonances. The spectral positions of the resonances are tuned through the width of the single nanowires. Additionally, the plasmonic gratings show a strong polarization dependency due to their one-dimensionality. In contrast, the pure organic system has a polarization-independent emission between 570 and 900 nm when excited with blue light, whereas no photoluminescence can be detected from the bare plasmonic system for the same illumination conditions. For the hybrid system, the intensity, the shape of the emission spectrum, and the polarization of the emission clearly correlate with the optical properties of the plasmonic nanowires. Depending on the optical properties of the plasmonic system, different emission bands of the organic thin film can be enhanced.

Ultrafast optical switching based on mutually enhanced resonance modes in gold nanowire gratings.

We report an efficient ultrafast optical switching device consisting of periodically arranged gold nanowires, which were produced by the multistage deposition of colloidal gold nanoparticles into deep grooves, so that they are as high as 220 nm and continuous as long as 20 mm. Due to the large thickness of the gold nanowires, two resonance modes became efficient and mutually enhanced: the waveguide resonance mode and the Bragg microcavity resonance mode. These resonance modes are based on the same diffraction conditions and have a completely overlapped spectroscopic response. Thus, a sharp resonance mode with a large amplitude and a steep rising edge is observed in the optical extinction spectrum at normal incidence. Strong optical excitation induced a red shift of the resonance spectrum and resulted in an enhanced optical transmission spectrum with a narrow bandwidth and a high response speed. Such an optical switching device with new physics has potential applications in optical logic circuits and integrated optics.

Multichannel high extinction ratio polarized beam splitters based on metasurfaces

Separating lights into different paths according to the polarization states while keeping their respective path’s polarizations with high purification is keen for polarization multiplex in optical communications. Metallic nanowire gratings with multi-slits in a period are proposed to achieve polarized beam splitters (PBSs) in reflection and diffraction. The setting of multi-slits largely reduces the reflection of photons with a transverse magnetific field via the plasmonic waveguiding effect, which leads to highly polarized output lights with extinction ratio larger than 20 dB in each channel. The proposed reflection/diffraction PBSs enrich the approaches to control the polarization states with the advantages of wide incident angles and flexible beam splitting angles.

Zinc Oxide nanowire gratings for light absorption control through polarization manipulation

Light-matter interaction has recently become an intense area of research in the field of photonic devices. Absorption control in semiconductors plays an important role in device performance, especially for plasmonic waveguides. Zinc Oxide (ZnO) is a known material for many photonic applications, where nanowires show quantum confinement effects in the ultraviolet and visible ranges. For applications requiring high-efficiency coupling from single-photon emitters and in ultra-sensitive optical sensing devices, the confined modes are highly desired. This is because surface plasmons enable the confinement and transport of light in highly-sub-wavelength volumes. In this study, we report a theoretical investigation of the change in absorption of intrinsic ZnO at the ZnO-silicon interface by a collimated light at variable incident angles. A confined wave or the weak plasmonics wave is created in the boundary region with a zone radius of 20 nm. The incident center wavelength is selected as 367 nm, which corresponds to the maximum absorption peak of the ZnO. The results show highly polarization dependent ZnO nanowire-silicon absorption, where the transmittance and reflectance vary with changes in the incident polarization. The confined electric field within the structure can be enhanced further by increasing the input power which varies between 1 and 5 W. An electric field of 1.4 × 105 V/m is confined within a small zone, where high transmittance (for incident angles smaller than 80°) and reflectance (for the incident angles greater than 80°) are demonstrated for the zeroth-diffraction order. Consequently, the minimum absorption loss within the configuration occurs for the zeroth-diffraction order.

Polarization transmission mechanism analyzation of bi-layer nanowire polarizer

The polarization transmission of bi-layer nanowire polarizer is analyzed physically by using equivalent medium theory and Fabry–Pérot resonate theory. The principal of the two theories are explained briefly. The analyzation of grating period, duty cycle and metal height on polarization transmission can be also applied to other type of nanowire polarizers. The critical period of the grating is given. The effects of the grating parameters on polarization performance are analyzed systematically on physical level. The extraordinary optical transmission of TM and specially TE polarization light through bi-layer nanowire grating is analyzed. The analyzation of the polarization transmission mechanism will be helpful for the design and fabrication of the gratings with good polarization properties.

Mechanism analyzation of the effects of grating parameters on polarization transmission of single-layer nanowire gratings

Using equivalent medium theory, surface plasma resonance theory and Fabry–Pérot resonance theory, transmission mechanism of single-layer nanowire polarizer is systematically analyzed. Concept of skin depth is used to explain the effect of grating material on polarization transmission. Two transmission minimum points in the curve of grating period versus transverse magnetic transmission are analyzed quantitatively. Effects of grating duty cycle, height and type on polarization transmission of single-layer nanowire polarizer are also analyzed. The requirements of designing single-layer sub-wavelength metal gratings with good polarization properties are given. The analysis of the transmission mechanism of sub-wavelength metal gratings will be helpful for the design and fabrication of the gratings with good polarization properties.

Enhancing light absorption in organic semiconductor thin films by one-dimensional gold nanowire gratings

The interaction of metallic plasmonic nanostructures and organic semiconductor thin films plays a crucial role in engineering light harvesting and energy transfer processes, e.g., for optoelectronic applications. Plasmonic resonances of the metal structures can be used to increase the light emission or absorption of organic molecules. Here small molecules are employed since they can form organic layers with a defined crystalline order and orientation of the transition dipole. Extinction measurements combined with numerical simulations of a hybrid system consisting of a gold nanowire grating and a thin film of diindenoperylene (DIP) are reported. The experimental results are compared to the simulations and indicate an enhanced absorption in the wavelength region corresponding to the transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital of DIP. This enhancement is found to be related to the localized field enhancement near the individual nanostructures as well as to grating-induced effects. Notably, the hybrid system also exhibits parallel lattice resonances, which have recently been discussed for two-dimensional (2D) gold nanostructure arrays. In this study a hybrid plasmonic-organic small molecule system exhibiting these modes is investigated. The results for this model system show a way to modify the optical properties of plasmonic nanostructures by collective effects to achieve stronger light-matter interaction in a wide range of hybrid plasmonic systems.