Here we have investigated the strong coupling of the guided modes with different orders in graphene-based onedimensional (1D) dielectric grating structures in the visible wavelengths. We found that the guided mode resonances (GMR) with different orders can strongly couple with each other under the oblique incidence of light. Absorption spectral response exhibits a distinct spectral anti-crossing with the Rabi splitting up to 59.8 meV. Simulation results further show that the strong coupling of GMR modes enables the bound state in the continuum (BIC) in this coupled system, which can be flexibly modulated by adjusting structural parameters. The proposed hybrid grating structures will benefit the applications in on-chip optical filtering, sensing, and optoelectronic detection.
Here we propose a metasurface consisting of asymmetric dielectric tetramer arrays, which can realize a polarization-sensitive light modulation through toroidal dipole resonance (TDR) in the near-infrared (NIR) region. We found, by breaking the C4v symmetry of the tetramer arrays, two narrow-band TDRs can be created with the linewidth around 1.5 nm. Multipolar decomposition of scattering power and electromagnetic field distribution calculations confirm the excitation of TDRs. Our simulation results show that 100% modulation depth in light absorption and selective field confinement can be achieved by changing the polarization orientation of the incident light. Our findings will prompt versatile applications in optical switching, storage, polarization detection, and light emitting devices.
Strong and narrow-linewidth circular dichroism (CD) spectroscopy promises potential applications in bio-chemical sensing and detection of the weak chirality in natural molecules. Here we proposed a chiral metasurface formed by the asymmetric metal double split ring resonator (DSRR) arrays, the circular dichroism (CD) of which has been investigated. The maximum CD for absorption response of the metasurface can reach 0.61 with an ultra-narrow spectral linewidth of 9.6 nm in the mid-infrared (MIR) band. Our calculation results show that the chiral metasurface can support two surface lattice resonance modes for the left circularly polarized (LCP) and right circularly polarized (RCP) light. The narrow linewidth of CD is enabled by the spin-selective high-Q resonance modes with a differential absorptivity for LCP and RCP light. Our findings shed light on the potential applications in spin-selective perfect optical absorption, high-sensitive polarization detection, and chirality sensing.
We have theoretically studied the strong coupling of the surface plasmon polaritons (SPP) and magnetic polaritons (MP) modes in an Au grating/dielectric/Au resonance structure in the near-infrared waveband. Our results show that SPP and MP modes can strongly interact with each other at the metal grating/dielectric/metal (MDM) interface, leading to a large Rabi splitting. We also find that the light absorptivity in the high- and low-frequency branches within the anticrossing region are abnormally different. Moreover, the simulation results indicate that strong SPP-MP coupling can be tuned by modulating the geometric parameters of the structure. The unique characteristics of strong coupling of SPP and MP modes in this simple MDM hybrid structure will be helpful in the design of various polaritonic devices.
Strong and controllable circular dichroism (CD) is of great significance in enormous applications of life science. Here we have theoretically investigated the CD response in an Au split-ring resonator (SRR)/graphene nano-ribbon arrays on a metal substrate. The circular dichroism (CD) intensity in the proposed structure can approach 50%. Our theoretical investigation indicate that the strong CD is arisen from the symmetry breaking with the longitudinal plasmonic coupling in this hybrid system. More interestingly, we find that the strong optical CD can be very robust to the change of geometrical parameters of SRR and graphene nanoribbon as well as their vertical separation. Our design provides a new route for developing the compact and robust optical chiral devices in application of biochemical sensing and optical communication.
In this work, high resonant reflection of light has been investigated in an atomic thickness resonator consisting of monolayer graphene nanosquare arrays at mid-infrared frequencies. Our numerical results show that more than 90% light reflectivity can be realized due to excitation of dipole resonance in the gap of graphene arrays in this system. Moreover, it is found the high resonant reflection is nearly independent of polarization over a wide-angle range. The resonant wavelength can be dynamically modulated by changing the geometry of the structure or adjusting the graphene chemical potential. Our findings provide new opportunities for the development of optical reflective devices, nano-antenna and highly integrated devices with atomic thickness.
In this work, we theoretically investigate the strong coupling of Tamm Plasmon Polaritons (TPP) in a graphene/DBR/Ag hybrid structure. It is found that TPP can be generated at both upper graphene and lower Ag interfaces, which can strongly couple with each other, allowing strong light-matter interaction with dual-band perfect absorption. Numerical results reveal that resonance frequency of hybrid modes can be tuned by adjusting geometry parameters or dynamically modifying graphene Fermi energy. Coupling strength for the TPP hybrid modes exhibits a large tuning range, from large Rabi splitting to a very narrow induced transparency. The tunable TPP strong coupling with a dual-band perfect absorption in this simple layered system is potential in developing a broad range of graphene-based optoelectronic devices.
In this paper, we have theoretically investigated the absorption response in a monolayer MoS2 covered one-dimensional dielectric grating structure at visible region. Through RCWA calculation, a dual-band total optical absorption has been numerically obtained in this proposed resonance structure. It has been demonstrated that the dual-band total absorption is enabled by the guided resonances with the critical coupling. Moreover, our calculation results also show that the resonance absorption wavelength could be controlled by choosing the proper structural parameters of this system. The ultra-high dual-channel light absorption offered by this simple and compact geometry may lead to the multiple-channel photonic devices in applications of optical detecting, sensing, storage and communication.
An asymmetric transmission device has been presented to realize high-performance one-way transmission at visible frequencies. This device consists of a pair of non-symmetric pyramid-shaped silicon gratings separated by a metal/dielectric multilayer structure (MDMS). Simulation results demonstrates that, compared with conventional Cr grating, MDMS with pyramid-shaped silicon gratings will greatly enhance the coupling and decoupling between the propagating waves in free space and the high frequency modes in MDMS, rendering an improved oneway transmission performance. The improved one-way transmission performance offered by our design may hold great potential in designing the optical isolator and polarizer for ultra-compact photonic integrated circuit.
The optical and acoustic fields of stimulated Brillouin scattering (SBS) effect in the As2S3 chalcogenide suspended-core microstructured optical fibers (MOFs) are investigated by the finite-element method (FEM). The optical and acoustic fundamental modes at 1550 nm are analyzed with the core diameters of the MOFs varying from 1.0 to 6.0 μm. For each case, the holes of the MOFs are filled with different materials such as trichlormethane (CHCL3), alcohol and water. When the core diameter is 6.0 μm, the maximum peak intensity of the optical fundamental mode is in the case with air holes, while the minimum value is in the case filled with CHCL3. The ratio of difference is ~0.66%. The minimum peak intensity of the acoustic fundamental mode is in the case with air holes, while the maximum value is in the case filled with water. The ratio of difference is ~0.13%. The same rule occurs in the fiber cores of 4.5, 3.0 and 2.0 μm, where the decreases of ~0.97%, 1.48%, 1.94% for optical field and the increases of ~0.24%, 0.34%, 0.74% for acoustic field are obtained, respectively. When the core diameter is 1.0 μm, ratios of difference for optical and acoustic fields are much higher than those in the cases of 2.0-6.0 μm, which are ~3.55% and 29.13%, respectively. The overlap factors between optical and acoustic fields are calculated, which are changed with the core diameter and the filled material in holes. Our results will be helpful to strengthen or suppress the SBS effect in practical applications.
Chalcogenide microstructured fibers (MOFs) have great advantages for supercontinuum (SC) generation in mid-infrared
(MIR) region, because they possess the properties of high nonlinearity and wide transmission window, simultaneously.
The nonlinear parameters of chalcogenide MOFs can be higher by several tens or hundreds than those of silica, fluoride
and tellurite fibers depending on the material components and fiber structures. Chalcogenide MOF can be transparent
from visible up to the infrared region of 12 or 15 μm depending on the compositions. In this paper, we demonstrate the
SC generation in two kinds of suspended-core chalcogenide MOFs with different material components and fiber
structures. One is an As2S3 MOF with three-hole structure (Fiber I). The other is an As2S5 MOF with four-hole structure
(Fiber II). For Fiber I, the SC range of 3020 nm (from 1510 to 4530 nm) were obtained in a 2.4 cm fiber, when pumped
by the wavelength at 2500 nm. The SC extends to the wavelengths longer than 4 μm. For Fiber II, the SC range of 4280
nm (from 1370 to 5650 nm) is generated in a 4.8 cm fiber when pumped by the wavelength at 2300 nm, which covers
more than two octaves. Compared to the SC generated in Fiber I, the SC spectral range in Fiber II has been increased by
more than 1200 nm due to the better transmission property of the As2S5 glass; the SC extends to the wavelengths longer
than 5 μm.
Photolithography is widely used to transfer a geometric pattern from a mask to a photoresist film, but the minimum
feature sizes are limited by diffraction through the mask. Focused ion beam and electron beam lithography can be used
when higher resolution is desired, but the write times are long and costly. Deep ultraviolet interference lithography,
which is a maskless technique, can be used as an alternative to produce high resolution patterns with feature sizes as
small as 100 nm. Since double negative metamaterial superlenses can be used for super-resolving and imaging subwavelength
objects, there is a need for fabricating such objects to characterize the performance of these metamaterials.
In this paper, simulations using standard finite element methods are first used to verify super-resolution and near-field
imaging at 405 nm for such objects using a metamaterial superlens previously fabricated from silver and silicon carbide
nanoparticles. Thereafter, results of fabrication and characterization of sub-wavelength objects using molybdenum of
typical thickness 50 nm initially sputtered on a glass substrate is presented. A deep ultraviolet laser source at 266 nm is
used. An anti-reflection layer followed by a high resolution negative tone photoresist is coated on the top of the
molybdenum film. The cross-linked photoresist created after the development and bake processes is used as a mask for
etching. Fabrication of the sub-wavelength object is completed using reactive ion etching in fluorinated plasma. Both
1D and 2D patterns are fabricated. The quality of the sub-wavelength objects during fabrication is checked using
scanning electron microscopy, and the 1D object is characterized using TE and TM polarized illumination.
In this paper, the influence of terminal layers on the characters of transmission and power flux in metal-dielectric
multilayer metamaterial (MDMM) has been systematically investigated. Calculation results demonstrate that optical
propagation and optical sigularity in multilayer structure are very sensitive to the thickness and materials of terminal
layers. In addition, we find the termination will greatly affect the propagation performance in form of singularities of
energy flux in MDMM and 100% visibility in superresolution process is always characterized by the appearance of the
singularities (saddle point) in imaging space. Our research will be helpful to actively engineer the energy flux in
nanostructures, especially in real time superresolution imaging, solar cell, nanolithography, etc.
Symmetric metallo-dielectric multilayered stacks (MDMS) are investigated to improve the spatial resolution of subwavelength imaging operated in canalization regime. Simulation results revealed that subwavelength imaging capability is very sensitive to the thickness and material of the MDMS terminal layers. Furthermore, the coupling and decoupling of the Bloch modes in MDMS, between the object and image space, strongly depend on the terminal layer parameters which can be tuned to achieve the optimal imaging improvement. In contrast to metal-dielectric periodic MDMS, using MDMS with the developed symmetric surface termination, subwavelength imaging with optimal intensity throughput and improved field spatial resolution (∼20.4% ) can be obtained. Moreover, optical singularity, in the form of Poynting vector saddle point, has been found in the free space after lens exit for the two kinds of symmetric MDMS that exhibit improved superresolution imaging performance with 100% energy flux visibility. The improved subwavelength imaging capabilities, offered by this proposed termination design method, may find potential applications in the areas of biological imaging, sensing, and deep subwavelength lithography, and many others.
A designed multilayered metamaterial cavity formed by the metallo-dielectric multilayer structure (MDMS) and a nano
Aluminum layer coated substrate is exploited to achieve the sub-20 nm patterns feature sizes at the wavelength of 248
nm with p-polarization. The filtering and SPP cavity resonance coupling provided by this MDMS cavity regime enable
the SPP interference patterns with high uniformity and intensity output in the photoresist (PR) layer. Furthermore,
compared with the conventional grating metal waveguide structure, this lithography system demonstrates the better
stability of patterns period against the cavity thickness variation. The enhancement and the longitudinal extension of SPP
localized field offered by the proposed cavity scheme will provide a potential way to obtain the lithography patterns with
improved depth, contrast and perpendicularity.
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