Metal-dielectric Grating Research Articles

Design of broadband metamaterial near-perfect absorbers in visible region based on stacked metal-dielectric gratings

A broadband near-perfect absorber in the visible region has been designed in this paper. This absorber consists of an alternating stack of metallic gratings and dielectric layers on the basis of a metallic substrate. Absorptivity and electromagnetic field distributions of the structure via the finite difference time domain (FDTD) method have been stimulated. The results show that the average absorptance of the absorber exceeds 95.2% in the wavelength range from 350 nm to 650 nm. The enhanced absorption can be ascribed to several mechanisms including surface plasmon polaritons, magnetic polaritons, and Fabry–Perot resonances. Besides, geometric effects on the resonance wavelengths have been investigated. Moreover, the effects of oblique incidence and polarization states on the spectral absorption have been analyzed. This designed absorber will be worth applying in solar energy harvesting via combining the study results mentioned above.

Reducing electric-field-enhancement in metal-dielectric grating by designing grating with asymmetric ridge

Diffraction gratings are an essential optical component of high-power, short-pulse lasers. The maximum output of high-power pulsed lasers is always determined by laser resistance of gratings and this resistance is strongly dependent on the local near electric field intensity in the grating structure. We presented a novel method of reducing electric-field-enhancement in metal-dielectric grating by designing asymmetric grating ridge while maintaining high diffraction performance. Compared with the common isosceles trapezoidal grating, the grating with asymmetric ridge got a 0.04% reduction of diffraction efficiency in TE polarization at 1053 nm incident wavelength but a 21.3% reduction of maximal electric-field-enhancement in grating structure. This method can be applied to any surface-relief gratings to reduce the electric-field-enhancement for improving the laser induced damage threshold (LIDT) of grating and supporting the grating-based chirped pulse amplification (CPA) system to develop into higher peak-power levels.

Wideband reflective quarter-wave plates based on subwavelength mixed metal dielectric gratings

A wideband reflective quarter-wave plate based on the mixed metal dielectric subwavelength grating (SWG) is designed and analyzed. The wideband quarter-wave plate works at wavelengths around 1.55 μm and it can realize high efficiency and uniform phase retardation. The diffraction efficiency is higher than 97% and phase retardation between TE and TM polarizations deviates from ideal value π/2 less than 3° for wavelengths from 1.438 μm to 1.651 μm. The conversion from linearly to circularly polarized waves is simulated by using FDTD algorithm, which shows high performance of the optimized quarter-wave plate. Numerical calculations demonstrate that the optimized quarter-wave sustains large tolerance for fabrication. The wideband mixed metal dielectric reflective quarter-wave plate should be useful in polarized laser systems.

Quadrupole mode plasmon resonance enabled subwavelength metal-dielectric grating optical reflection filters.

A metal-dielectric subwavelength grating structure was investigated for making single-peak narrow linewidth optical reflection filters in the near-infrared region. The subwavelength grating filter structure consists of a one-dimensional periodic array of metal (gold) and dielectric (Al2O3) elements on a dielectric substrate. Optimized reflection filters have a single reflection peak with ~10 nm linewidth in the infrared region over a wide spectral band. Finite-difference time-domain (FDTD) simulations and multipole analysis show that the narrow linewidth reflection is due to the coupling of the Rayleigh anomaly wave to the quadrupole plasmon resonance mode of the subwavelength metal-dielectric grating. Additionally, it was found that the contrast of the indices of refraction of two dielectric materials in the subwavelength structure is critical for realizing optical filter effect.

Plasmonic sensor with variable claddings based on metallic slit arrays

We propose a plasmonic sensor with variable refractive index (RI), which exhibits high sensitivity and extraordinary optical transmission (EOT). Its variable RI is attributed to its dielectric layers and metallic slit arrays. According to simulation results, the third resonant wavelength has a wavelength sensitivity of 800 nm/RIU and an ultra-high transmittance of 0.8 by adjusting the RIs of the upper and lower dielectrics, incident light angle, and structural geometric parameters. With its unique features, the proposed structure holds considerable potential for extensive application to metal–dielectric grating sensors operating at visible and near-infrared frequencies.

Optimal Design of Wavelength Selective Thermal Emitter for Thermophotovoltaic Applications.

We theoretically and numerically demonstrate optimal design of wavelength selective thermal emitter using one-dimensional (1D) and two-dimensional (2D) metal-dielectric gratings for thermophotovoltaic (TPV) applications. Proposed design consists of tungsten (W) and silicon dioxide (SiO2) gratings which can withstand high temperatures. Radiative properties of 1D grating were calculated using a numerical method, while effective medium approximation was used for 2D gratings. Optimal designs were obtained such that output power is maximum for GaSb photovoltaic (PV) cell at emitter temperature of 1500 K and radiated energy for longer wavelengths is limited to a low value. A constrained optimization was performed using genetic algorithm (GA) to arrive at optimal design.

Simultaneous generation and focus of radially polarized light with metal-dielectric grating metasurface

Simultaneous manipulation of light polarization and phase possesses great significance for modern optical technologies. Here we propose metal-dielectric gratings capable of tailoring the polarization and phase of light based on polarization filtering with the polarization extinction ratio exceeding 10dB and the transmittance higher than 65%. The standard radially polarized (RP) light with axially symmetric polarization distribution can be generated by using arrayed grating with gradient phase under the illumination of circularly polarized (CP) light. Besides, a RP metasurface lens with high numerical aperture is presented, which can convert the CP light into the focused radially polarized light at wavelength of 632.8nm. This compact and efficient approach would have potential applications in beam manipulation, super-resolution imaging and integrated optics system.

A wide-angle broadband polarization-dependent absorber with stacked metal-dielectric grating

We report an absorber in the mid-infrared regime by using stacked metal-dielectric grating structure. The simulation results show that the minimal absorption magnitude is larger than 0.8 in the broadband range for angles up to 60° for TM polarization (magnetic field is parallel to grating grooves). At the same time, absorption for TE polarization (electric field is parallel to grating grooves) is negligible. Furthermore, such broadband absorption for TM polarization can be tuned by shrinking or enlarging the grating parameters. This absorber is a good candidate for potential applications such as polarization detectors and polarizers.

Suppression of the Zeroth Order by a Mixed Metal Dielectric Grating

A mixed metal dielectric grating is designed and analyzed to suppress the zeroth order in the reflection region instead of the transmission structure. There are no ±2nd orders for the grating period in this paper, which leads to high efficiencies in the ±1st orders. Efficiencies of 48.36% for TE polarization and 48.34f#x0025; for TM polarization can be diffracted into the ±1st orders at the incident wavelength of 1550 nm, respectively. While in the zeroth order, there are only efficiencies of 0.21% for TE polarization and 0.23% for TM polarization. For the transmission grating, efficiencies are usually modulated cosinoidally based on a modal method. It is difficult to achieve wide fabrication tolerance for the etching depth. For the reflective grating in this paper, the wide etching depth range is tolerated, particularly for TM polarization. The low-contrast structure and good performance can make the reflective grating useful, with the zeroth order suppressed.

Polarizing grating color filters with large acceptance angle and high transmittance.

We design and simulate a polarizing color filter with a sub-wavelength metal-dielectric grating. It manifests several advantages: a large acceptance angle (up to ±50°), high transmittance (74.3%-92.7%), low absorption loss (∼3.3%), and a high extinction ratio. This polarizing color filter can be integrated into a liquid-crystal display (LCD) backlight system to simultaneously recycle the light according to its color and polarization. In combination with a specially designed directional backlight, this newly proposed LCD system can theoretically improve optical efficiency up to ∼2.5×, and also provides a large ambient contrast ratio and a wide view. Our approach enables an ultra-low-power LCD without using the complicated field-sequential-color technique.

Waveguide-metal–dielectric bi-layer gratings for reflective filtering and color security

A multi-material structure composed of a linear polarizer and a dielectric sandwiched between two metal–dielectric gratings of with л phase shifts and embedded in dielectric is proposed. Its properties of reflection resonance together with filtering ability of visible light are discussed thoroughly and main factors of impacting its functions are identified. Both such properties and line-shapes of its spectra can be effectively trimmed by thickness, symmetry, period and metal material of two gratings. The behaviors of its single-peaks and peak-splits in spectra in combination with peak-shifts can generate uncommon color variation of interchanges in reflection based on structured coloration. Various color filters of reflection operating in visible light can be realized by it as well as intricate color effects arising from structures. This structure is valuable for applications of filtering, decoration and security.

Broadband absorption enhancement in ultrathin-film solar cells by combining dielectric nanogratings and metallic nanoribbons

Optical absorption improvement and cost reduction of thin-film solar cells have been long-time issues. These two aims are achieved simultaneously by combining metallic nanoribbons and dielectric gratings at the front side of ultrathin-film amorphous silicon solar cells. Surface-plasmon-polariton waves excited by the nanoribbons at the long wavelength co-operates with Uller-Zenneck waves and cavity resonances excited by the gratings at the short wavelength with little cross-effect, leading to a complementary absorption enhancement of 31% when compared to planar structure. In addition, this design exhibits wide-angle absorption as well as a high fabrication tolerance. Compared to the previous work combining different mechanisms, this design provides fewer fabrication steps and an easier approach. Moreover, the nanoribbons can be used as a transparent conducting electrode for a low-cost alternative to expensive indium tin oxide thin-film.

Polarization-independent metal-dielectric grating with improved bandwidth

A polarization-independent reflective grating with improved bandwidth is presented based on the mixed metal-dielectric grating. The novel grating is composed of the substrate, the metal slab, two dielectric layers, and the covering layer. The grating parameters are optimized for the special duty cycle of 0.6 at an incident wavelength of 1550 nm used in dense wavelength division multiplexing (DWDM). With the designed grating, high efficiency can be diffracted into the reflective –1st order for both TE and TM polarizations, where the polarization-independence is exhibited. Most importantly, the efficiency of more than 90% can be achieved within the incident wavelength bandwidth of 1262–1686 nm, where the bandwidth is improved greatly compared with the reported surface-relief single-layer grating. The reflective grating can have advantages of high efficiency, polarization-independence, and wide bandwidth, which should be useful for DWDM applications.

A mixed metal dielectric sandwiched grating for polarization-selective reflection

A mixed metal dielectric sandwiched grating is described for polarization-selective reflection. The novel grating is composed of substrate, metal slab, two dielectric grating layers, and covering layer. The polarization-selective grating is optimized by using rigorous coupled-wave analysis for the usual duty cycle of 0.5. With the optimized grating parameters, reflective efficiency of 96.49% can be diffracted into the −1st order for TE polarization. And two-port output of 48.26%/48.27% can be diffracted into the 0th and the −1st orders for TM polarization. Polarization-selective reflection with good performance can be obtained by the mixed metal dielectric sandwiched grating. The usual duty cycle of 0.5 makes it easy and simple to be fabricated for practical applications. Moreover, the polarization-selective beam splitter based on the mixed metal dielectric sandwiched grating has advantages of wide incident wavelength range for TE polarization and angular bandwidth for TM polarization.

Orders of magnitude enhancement of optical nonlinearity in subwavelength metal-nonlinear dielectric gratings

We show that the optical properties of a metal-nonlinear dielectric grating can be precisely described by a uniform nonlinear dielectric slab. Based upon such a metamaterial mapping, we show that the effective optical nonlinearity in a metal-dielectric grating can be enhanced by orders of magnitude higher than that of the underlying nonlinear dielectric material, is broadband, and can be operated at a low quality-factor regime so as to have an extremely short intrinsic temporal response of a few picoseconds. Furthermore, we demonstrate extraordinary harmonic generation efficiency enhancement and large threshold-power reduction in bistability.

Spectral resonant properties of reflected light for metal dielectric subwavelength gratings in visible regions

A metal-dielectric grating consists of alternating metal and dielectric materials with period less than single wavelength of visible radiations. Optical behaviors of reflection spectra of this grating for s-polarized and p-polarized incident white light are studied systematically. For reflected light, it is the p-polarized light rather than s-polarization shows unusual optical behaviors with characteristics of single-peak spectra, higher peak efficiencies of higher than 75% and lower off-resonant efficiencies. The spectral width of p-polarized light with desirable frequency-selective functions is much wider. There exist two resonant areas for p-polarizations extending toward each other as filling factors increase, and positions of the resonances are mainly determined by grating periods existing linear relationships between them. For making positions of resonances occur in visible wavelengths, filling factors and grating periods should be respectively designed between 0.5 and 0.6 and between 0.25 and 0.45 µm. The newly observed properties of p-polarized lights can be used to exploit novel devices for reflection applications in the fields of optical securities and color filters.

Polarization-independent wideband mixed metal dielectric reflective gratings

A polarization-independent wideband mixed metal dielectric grating with high efficiency of the -1st order is analyzed and designed in Littrow mounting. The mixed metal dielectric grating consists of a rectangular-groove transmission dielectric grating on the top layer and a highly reflective mirror composed of a connecting layer and a metal film. Simplified modal analysis is carried out, and it shows that when the phase difference accumulated by the two propagating modes is odd multiples of π/2, the diffraction efficiency of the -1st order will be high. Selecting grating depth and duty cycle for satisfying the phase difference condition for both TE (electric field parallel to grooves) and TM (magnetic field parallel to grooves) polarizations, a polarization-independent high-efficiency grating can be designed. Using rigorous coupled-wave analysis and a simulated annealing algorithm, geometric parameters of the reflective grating are exactly obtained. The optimized grating for operation around a wavelength of 800 nm exhibits diffraction efficiencies higher than 90% for both TE and TM polarizations over a 120 nm wavelength bandwidth. The simplified modal analysis can be applied in other types of reflective gratings if the top layer is a dielectric transmission grating.

Field singularities at lossless metal–dielectric arbitrary-angle edges and their ramifications to the numerical modeling of gratings

I extend a previous work [J. Opt. Soc. Am. A, 738 (2011)] on field singularities at lossless metal-dielectric right-angle edges and their ramifications to the numerical modeling of gratings to the case of arbitrary metallic wedge angles. Simple criteria are given that allow one knowing the lossless permittivities and the arbitrary wedge angles to determine if the electric field at the edges is nonsingular, can be regularly singular, or can be irregularly singular without calculating the singularity exponent. Furthermore, the knowledge of the singularity type enables one to predict immediately if a numerical method that uses Fourier expansions of the transverse electric field components at the edges will converge or not without making any numerical tests. All conclusions of the previous work about the general relationships between field singularities, Fourier representation of singular fields, and convergence of numerical methods for modeling lossless metal-dielectric gratings have been reconfirmed.

Design and analysis of multilayered structures with metal–dielectric gratings for reflection resonance and color generation

A multilayered structure incorporating a metal-dielectric subwavelength grating, with the characteristic of polarization separation for visible light and the capability of creating reflection resonance and distinctive polarization-dependent color effects, is proposed. Its reflection resonance and color for TE and TM polarizations are discussed, as well as the influence of its structural parameters on them. Moreover, a reflection filter with characteristics of red for TE-polarized light, green for TM-polarized light, and yellow for daylight is designed and fabricated by replacing its grating region with a sinusoidal grating, and its related characteristics also are verified. The structure and its properties can achieve practical applications in various fields, such as color security, image reproduction, color filtering, and polarization-based information hiding.

MEMS-based plasmon infrared emitter with hexagonal hole arrays perforated in the Al-SiO2-Si structure

A micro-machined plasmon infrared emitter with hexagonal hole arrays perforated in the Al/SiO2/Si structure is presented. The silicon-on-insulator wafer was employed to fabricate the hexagonal photonic crystal infrared emitters using micro-electro-mechanical system (MEMS) technology. The Al/SiO2/Si structure perforated with periodic hexagonal hole arrays was resistively heated using direct-current voltage to active the boron-doped silicon membranes. The electrical characteristics and emission spectrum of infrared emitters under different excited voltage conditions were measured. Additionally, the reflection, transmission and absorption of light were also characterized to reveal the mechanism of narrowband-enhanced emission. The experimental results indicate that the surface plasmon polaritons (SPPs) caused by the diffraction of the thermal radiation impinge on the metal–dielectric grating and play an essential role in the extraordinary optical transmission and enhanced emission of subwavelength hole arrays. The constructive interference between the thermal radiation and the SPPs enriches the emission spectrum on the condition that the phase match relation is satisfied. It is demonstrated from the measured results of modulation performance and thermal imaging of emitters that the thickness of membranes and the thermal isolation between membranes and supporting frame structure have a significant influence on the modulation rate, emission intensity and the suppression of the background emission.