Metal-dielectric Grating Research Articles

Optimizing the design of highly linearly polarized white LED with multilayer metal-dielectric grating structure

In order to emit a linearly polarized light and reduce energy loss for a white light emitting diode (LED), a multilayer metal-dielectric grating structure using GaN-based blue LED is proposed. This multilayer structure is composed of three major functional layers: a fluorescent ceramics layer, a dielectric anti-reflection layer and a linear polarization grating layer. Fluorescent ceramics layer is integrated on the top of GaN-based blue LED, to achieve white light emission. In turn, a dielectric anti-reflection layer and a linear polarization grating layer are also integrated to obtain a higher transmission of white light and improve the conversion efficiency of linear polarization. The structural parameters of each functional layer, including period (150 nm), duty cycle (0.5), height of metal-dielectric grating (55 nm and 80 nm) and thickness of dielectric layer (15 nm), are simulated and optimized by finite-difference time-domain method. Then the multilayer structure is fabricated by UV nanoimprint and its transmission and polarization characteristics are tested. The results show that the transmittance and extinction ratio are higher than 50% and 33.8 dB in the wavelength range of 400–800 nm, and the maximum value can reach 91.3% and 41.3 dB, respectively. It is well verified by experiments that the proposed structure has a steady polarization performance of TM mode in the range of ±20°, which provides a fundamental guarantee for developing the potential applications of polarized white LED.

A metamaterial absorber with a multi-layer metal–dielectric grating structure from visible to near-infrared

In this paper, we propose a multi-layer metal–dielectric grating consisting of multi-layer nickel–silicon nitride (Ni-SiNX) grating over a metallic Ni substrate as an ultra-broadband near-perfect absorber. The structure is not only simple in structure, but also superior in performance. Numerical analysis of the structure shows that it has an absorption rate of 99.24% in the wavelength range of 400–2000 nm. To achieve ultra-broadband and high absorption properties, the suggested absorber simultaneously creates excitation of propagating surface plasmon resonance (PSPR), local surface plasmon resonance (LSPR), and Fabry–Perot (FP) cavity. By analyzing the absorption performance of different incident angles and polarization waves, it is demonstrated that the broadband near-perfect absorption of the absorber exhibits insensitivity to the angle of the incident light. In addition, we discuss the effects of various metallic materials and parameters of geometric structures on the absorption characteristics in detail. Finally, we discussed the suggested scheme’s potential in terms of solar energy capture. Therefore, we anticipate that our proposed absorber can be applied in solar energy harvesting as well as broadband thermal emission.

Design and Fabrication of Highly Selective Polarizers Using Metallic–Dielectric Gratings

Polarization imaging has been proven as an important technique for obtaining multi-dimensional information in complex environments. As the prevalent polarizers, metal gratings are widely used especially for focal-plane detection due to their flexibility and easy integration. However, high-performance polarization gratings with high transmittance and large extinction ratios typically need a large aspect ratio in design, resulting in more difficulties in fabrication with limited practical performances. In this study, we designed and fabricated a high-performance polarizer using metallic–dielectric gratings (MDGs). Through a single CMOS-compatible procedure that included electron-beam lithography (EBL) and a collimated thermal evaporation deposition process, we achieved a high TM transmittance (~90%) and a high extinction ratio (~100:1) in the experiment. We believe that our work provides an effective approach to high-performance polarization gratings, which could contribute to the development of on-chip integrated polarization imaging.

Hybrid metal-dielectric gratings (HMDGs) as an alternative UV-SERS substrate.

Ultraviolet surface-enhanced Raman scattering (UV-SERS) typically occupies an important position because the electronic absorption bands of many biomolecules are located in the deep-ultraviolet (DUV) or ultraviolet (UV) region. Practical application of UV-SERS still relies on uniform, reproducible, and affordable substrates. The conventional aluminum (Al) plasmonic nanostructures are mostly applied to act as UV-SERS substrates, but their intrinsic ohmic loss hinders their practical application. In this study, wafer-scale hybrid metal-dielectric gratings (HMDGs) consisting of aluminum and silicon (Al-Si) have been successfully fabricated as UV-SERS substrates to reduce ohmic dissipation and elevate the detection performance. Well-defined HMDG substrates exhibit tunable hybrid resonant modes in the UV and the visible regions. The adenine biomolecules deposited on HMDG substrates are used to perform SERS measurement with an excitation wavelength of 325 nm. The HMDG nanostructures can obtain as high as 5 orders of magnitude compared with that of Al film as UV-SERS substrates. The proposed HMDG nanostructures have a great advantage in detecting important biomolecules as UV-SERS substrates.

Strong Local Field Enhancement of Raman Scattering Observed in Metal-Dielectric Gratings due to Vertical Fabry-Perot Modes of Surface Plasmon Polaritons

The height dependence of Raman light scattering on organic molecules deposited onto thick one-dimensional metal-dielectric gratings is investigated theoretically and experimentally. We observe oscillations of the intensity of Raman light scattering as a function of the height of the metastructure's strips and demonstrate that these oscillations are explicitly associated with a type of Fabry-Perot effect. We show that the intensity of surface-enhanced Raman scattering can be additionally increased by local field enhancement (by an order of magnitude) at resonances of both pump and Stokes as well as anti-Stokes frequency, due to coupling of the surface plasmon polaritons on the top and bottom metal parts of the gratings via the vertical Fabry-Perot resonances over their middle dielectric part. A semianalytical one-mode model to describe the effect qualitatively is proposed. A significant deviation of the dispersion of Fabry-Perot-coupled plasmon polaritons from the surface-plasmon-polariton dispersion just folded into the first Brillouin zone is demonstrated.

Opaque pixel mask with a broadband absorbing metasurface: application to infrared detectors.

We present an imager architecture comprising dark and active pixels allowing the simultaneous measurement of photonic and dark current, which is of particular interest for low-photon-flux astronomical applications. The principle of operation relies on both the total opacity of a thin metallic screen of sufficient area and the anti-reflective properties of well-designed resonant metal-dielectric gratings made on the same screen. The concept is exemplified in the context of cooled HgCdTe hybrid detectors, at short- and long-wave infrared ranges.

Polarization dependent high refractive index metamaterial with metallic dielectric grating structure in infrared band

According to the theory of high refractive index of metamaterials, a composite structure of metal dielectric grating was designed to achieve high refractive index in infrared band. Based on the S-parameter inversion algorithm, we extracted the effective permittivity, the effective permeability, and the effective refractive index of the designed metamaterial. By changing the geometric parameters of the composite grating metamaterial structure, the effective refractive index of the designed metamaterial reaches more than 8.0 at the infrared resonance frequency. This is a high refractive index that many natural materials cannot achieve. It is noteworthy that the metamaterial structure has obvious polarization sensitivity. The metamaterial structure has both high refractive index and wide-band zero refractive index properties when different polarized light is incident. At the same time, we further investigate the influence of metamaterial geometric parameters on the effective refractive index of metamaterials. Also, we propose a double grating metamaterial structure to obtain more degrees of freedom of metamaterial on the effective refractive index.

Polarization-insensitive high-efficiency two-dimensional metal-dielectric grating by nanodisks arrays

In this paper, a two-dimensional (2D) reflective grating with nanodisks arrays (NDA) is described, which is capable of achieving high-efficiency and polarization-insensitive output of (−1, 0) order. The proposed grating has been optimized by the finite element method (FEM) at a central wavelength of 780 nm under Littrow mounting, where the grating achieves diffraction efficiencies of 98.01% and 97.54% at the (−1, 0) order for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively. In addition, the extinction ratios of TE and TM polarizations are 33.01 dB and 35.74 dB, respectively. The electric field distribution, wavelength bandwidth, angular bandwidth and fabrication tolerance of the 2D grating are analyzed in detail. The analysis shows that the proposed grating offers a significant improvement in wavelength (bandwidth of 14 nm) and angular (bandwidth of 6.4°) bandwidths compared to previously reported 2D gratings. At the same time, the tolerance analyses demonstrate the feasibility and advantages of NDA grating in practical manufacturing processes. The results are very helpful in understanding and designing 2D gratings, and the proposed grating has great application potential in 2D grating measurement system (GMS).

Antenna radome based on metal-dielectric gratings as angular filter at microwaves

This article is devoted to the analysis of numerical study results of printed angular filters scattering characteristics. It is shown these angular filters may be used as antenna radomes. Numerical results are obtained by full-wave simulation of frequency-selective surfaces with dielectric covers. The numerical research results of the scattering characteristics of a printed angular filter as antenna radome based on metal-dielectric gratings are presented. A comprehensive numerical study of microwave angular filters based on multi-element multilayer printed reflect arrays has been carried out. Constructive solutions for metal-dielectric structures in integral design, realizing the functions of angular filters, are found. These solutions are based on performed numerical studies. The problems of constructive implementation of multilayer planar spatially selective as angular filters are considered. These angular filters are integrated into the radiators and feeders of modern multi-element printed phased arrays. The problems connected with creation of such arrays are also considered. The numerical simulation results for angular filters based on metal gratings with dielectric covers are obtained. These results can be used to select the most rational options for the topology of metal-dielectric gratings. Such solutions may be useful for design of multifunctional radomes in microwave antenna systems. Based on the obtained numerical data, the possibilities of using flat gratings as angular filters in the composition of antenna radomes are considered. The spatial frequency-selective structures proposed in this work are performed as multi-planar printed gratings. These gratings are designed to ensure electromagnetic compatibility of closely spaced radio electronic sets. These radio electronic sets operate in close frequency ranges. They contain antenna arrays. These arrays are placed under the antenna radomes. At the same time, the installation of angular filters in the antenna radomes makes it possible to eliminate the appearance of unwanted grating lobes in the radiation patterns of sparse antenna arrays of promising radioengineering sets at microwaves.

Frequency selective antenna radome based on metal-dielectric gratings and perforated screens

This article is devoted to the analysis of numerical study results of printed frequency selective surfaces scattering characteristics. It has been shown that these frequency selective surfaces may be used as antenna radomes. Numerical results have been obtained by full-wave simulation of frequency-selective surfaces with dielectric covers. The numerical research results of the scattering characteristics of printed frequency selective surfaces as antenna radomes based on metal-dielectric gratings and thick perforated screens have been presented. A comprehensive numerical study of microwave frequency selective surfaces based on multi-element multilayer printed reflectarrays and thick perforated screens has been carried out. Constructive solutions for metal-dielectric structures in integral design, realizing the functions of frequency selective surfaces, have been found. These solutions are based on performed numerical studies. The problems of constructive implementation of multilayer planar spatially selective as frequency selective surfaces have been considered. These frequency selective surfaces are integrated into radiation systems of modern multi-element printed phased arrays. The problems connected with creation of such arrays have been also considered. The numerical simulation results for frequency selective surfaces based on metal gratings with dielectric covers have been obtained. These results can be used to select the most rational options for the topology of metal-dielectric gratings. Such solutions may be useful for design of multifunctional radomes in microwave antenna systems. Based on the obtained numerical data, the possibilities of using flat gratings as frequency selective surfaces in the composition of antenna radomes have been considered. The spatial frequency-selective structures proposed in this work are performed as multi-planar printed gratings. These gratings are designed to ensure electromagnetic compatibility of closely spaced radio electronic sets. These radio electronic sets operate in close frequency ranges. They contain antenna arrays. These arrays are placed under the antenna radomes.

Flat metal-dielectric grating with 100% retro-diffraction efficiency: rigorous theory

We have recently designed a new type of a flat metal-dielectric grating which is supposed to replace blazed diffraction gratings, providing very high −1st reflected diffraction order efficiency within a broad wavelength band, high durability, and relative ease of fabrication. In this communication we present a rigorous electromagnetic theory of the grating in the approximation of infinitely thin perfect metal and show that the properly designed grating can reach 100% diffraction efficiency in the Littrow configuration for either transversal electric (TE or s) or transversal magnetic (TM or p) polarizations. Properties of the grating are analysed and discussed in detail.

Spectral element method with modified Legendre polynomials for modal analysis of lamellar gratings.

We report on the derivation of a spectral element method whose originality comes from the use of a hierarchical basis built with modified Legendre polynomials. We restrict our work to TM polarization, which is the most challenging. The validation and convergence are carefully checked for metallic dielectric gratings. The method is shown to be highly efficient and remains stable for huge truncation numbers. All the necessary information is given so that non-specialists can implement the method.

Self-referenced refractive index sensor based on hybrid mode resonances in 2D metal-dielectric grating

In this paper, we propose a refractive index sensor with self-reference performance based on a two-dimensional grating structure, mainly consisting of periodic arrays of triple layer dielectric nanodisks and a continuous substrate separated by a thin gold film. Three reflection dips are observed and manipulated to realize self-reference and high sensing performance due to the excitation of magnetic dipole mode resonance, substrate mode resonance and metal layer assisted guide mode resonance. These hybrid modes have been explained by the distributions of the electric and magnetic fields in the nanostructure. A detailed analysis of the influences of material thickness on the optical properties of the proposed refractive index sensor is also investigated. Moreover, the proposed refractive index sensor demonstrates a high sensing performance, an important application for future biomedical applications, with a bulk refractive index sensitivity of 672 nm RIU−1 (RIU: refractive index unit) and figure of merit of 1050 RIU−1. Importantly, the function of self-reference is realized simultaneously. Finally, it also shows excellent sensing performance, with the maximum value exceeding 168 000 by measuring the light intensity change in the reflected light at a certain wavelength. This makes it much more suitable for applications in the field of portable detection.

Narrowband absorber based on magnetic dipole resonances in two-dimensional metal–dielectric grating for sensing

In this paper, we propose a two-dimensional metal–dielectric grating with dielectric nanoarrays on a thin gold film structure for refractive index sensing due to its near unity absorption at 1050 nm wavelength. Perfect absorption can be achieved due to the horizontal magnetic dipole coupling the free-space incident waves into surface plasmon-polaritons (SPPs). The effect of the geometrical parameters on the absorption spectra and sensing performance are studied. The preferred results show that the corresponding figure of merit is calculated to be 73.1 RIU−1, which shows a remarkable improvement than the previous reported sensors. Moreover, it also demonstrates excellent performance by measuring the light intensity change in the reflected light at a certain wavelength, which provides the possibility for low cost and portable detection.

Start current and growth rate in Smith\u2013Purcell free-electron laser with dielectric-loaded cylindrical grating

We present an analytic theory for Smith–Purcell device in which a cylindrical metal–dielectric grating was derived by an annular electron beam propagating along the grating axis. A dispersion relation is obtained for azimuthally symmetric modes. Also, the first-order and second-order growth rates of the modes which are in phase with the beam are compared. It is shown that the second-order growth rate gives a more accurate description of beam–wave interaction for beams with larger thicknesses, as well as grating slots, with smaller depths and greater lengths. The start current for BWO operation of the SP-FEL is presented too. The importance of the minimum value of start current is that above it, the SP-FEL will operate as an oscillator, even in the absence of external feedback. In this case, the group velocity of the synchronous evanescent wave is negative, while the electron beam travels in the forward direction. It is shown in this paper that the dielectric and grating parameters affect the value of start current. So, by changing these parameters, the minimum value for the start current can be obtained.

Multiphase resonant properties in metallic dielectric gratings with three-slits

The optical transmission properties in a three-slit metal grating with different mediums are studied. The results show that the tunable phase resonances and multiple phase resonances can be obtained by filling different mediums into the three slits of the straight channel grating. When the medium in the three slits is extremely asymmetric, the phenomenon of multiphase splitting becomes very obvious. In addition, based on the field distributions, multiphase resonant mechanisms have been proposed for the physical origins of the observations. In addition, a multi-channel selector is described by flexibly controlling the light through any slit of the grating. Compared with the conventional compound grating, this grating with different mediums has obvious advantages, such as simple structure, and ease of implementation.

Metal dielectric gratings with high femtosecond laser damage threshold of twice as much as that of traditional gold gratings

We report on the development of metal dielectric gratings (MDG) including two layers of gold film and a silica layer, which is simple and has enough broadband with 105 nm over 90%. The measured laser-induced damage threshold (LIDT) on the grating surface is 0.40 J/cm2 at a pulse duration of 32 fs, which is twice more than that of gold gratings, and the initial damage comes from nodule defects. Laser-induced ionization theory is first used to study the effect of nodule defects on LIDT of MDG and predict the maximum LIDT of the perfect MDG. The prediction value of the MDG without nodule defects is 0.60 J/cm2 on the grating surface, which has tremendous application potential in petawatt-class laser systems.

Influence of nodular defect size on metal dielectric mixed gratings for ultra-short ultra-high intensity laser system

With the development of the high power laser facilities, laser resistance of pulse compression grating is getting increased attention. The metal dielectric mixed grating (MDMG) is widely studied, because it has wide diffraction bandwidth, low surface stress and potential high threshold. The effect of nodular defect size on damage of MDMG is studied by experiments and theoretical analysis in two typical cases. The initial damages appear in the district of nodular defect due to local electric field enhancement induced by nodular defect, which is different with the initial damage located in grating pillar of the perfect MDMG. Laser induced ionization theory is introduced to describe the damage process and give a quantitative analysis on the relationship of laser damage and nodular defect size. It is concluded that local electric field enhancement in nodular defect area would cause the electron density to reach the critical value and lead to the damage occurrence, and nodule damage critical diameters are 1400 nm and 1500 nm respectively in case 1 (seed under the grating pillar) and case 2 (seed under the grating groove) which will lead to nodule damage initiation.

Enhancing THz generation in photomixers using a metamaterial approach.

Photomixers at THz frequencies offer an attractive solution to fill the THz gap; however, conventional photomixer designs result in low output powers, on the order of microwatts, before thermal failure. We propose an alternative photomixer design capable of orders of magnitude enhancement of continuous-wave THz generation using a metamaterial approach. By forming a metal-semiconductor-metal (MSM) cavity through layering an ultrafast semiconductor material between subwavelength metal-dielectric gratings, tailored resonance can achieve ultrathin absorbing regions and efficient heat sinking. When mounted to a tunable E-patch antenna, gratings also act as vertically biased electrodes, further enhancing photoconductive gain by reducing the carrier path length to nanoscales. Thus, through these multiplicative enhancements, the metamaterial-enhanced photomixer is projected to generate THz powers in the milliwatt range and exceed the Manley-Rowe limit for frequencies less than 2 THz.

Polarization-independent two-dimensional diffraction metal-dielectric grating

Two-dimensional (2D) diffraction gratings have been developed rapidly in several growing areas of research, but most of them were polarization sensitive with limitations toward practical applications. We report a 2D diffraction grating solution for achieving polarization-independent high efficiency property. The grating was designed and fabricated based on thin-film coatings, orthogonally lithography, and ion-beam etching technology. The measured average (−1, 0) order reflective diffraction efficiency (DE) is 74.8% (p-polarization) and 68.2% (s-polarization) from 770 nm to 790 nm and the lowest difference of DE between two polarizations is 0.593% at 785.5 nm incident wavelength of our sample.