Polarization Angle Of Incident Light Research Articles

Multifunctional terahertz device based on plasmon-induced transparency

Abstract Enhancing light-matter interaction is crucial in optics for boosting nanophotonic device performance, which can be achieved via plasmon-induced transparency (PIT). In this study, a polarization-insensitive PIT effect at terahertz frequencies is achieved using a novel metasurface composed of a cross-shaped graphene structure surrounded by four graphene strips. The high symmetry of this metasurface ensures its insensitivity to changes in the polarization angle of incident light. The PIT effect, stemming from the coupling of graphene bright modes, was explored through finite difference time domain (FDTD) simulations and coupled mode theory (CMT) analysis. By tuning the Fermi level in graphene, we effectively modulated the PIT transparent window, achieving high-performance optical switching with a modulation depth (88.9% < MD < 98.0%) and insertion losses (0.17 dB < IL < 0.51 dB) at a carrier mobility of 2 m2/(V·s). Furthermore, the impact of graphene carrier mobility on the slow-light effect was examined, revealing that increasing the carrier mobility from 0.5 m2/(V·s) to 3 m2/(V·s) boosts the group index from 126 to 781. These findings highlight the potential for developing versatile terahertz devices, such as optical switches and slow-light apparatus.

Graphene metamaterials-based plasmon-induced terahertz modulator for high-performance multiband filtering and slow light applications.

We proposed multilayered graphene (Gr)-based surface plasmon resonance-induced high-performance terahertz (THz) modulators with tunable resonance frequencies. Previously reported Gr metamaterials-based THz plasmonic modulators had small group delay, low extinction ratio (ER), and difficult-to-tune resonant frequency without changing structural parameters in the THz range. A comprehensive investigation employing the finite-difference time-domain (FDTD) simulation technique revealed high group delay, broad tunability independent of structural parameters, and large ER for our proposed quadband and pentaband plasmonic modulators. We obtained tunable group delays with a maximum of 1.02 ps and 1.41 ps for our proposed quadband and pentaband plasmonic modulators, respectively, which are substantially greater compared to previously reported Gr-based metamaterial structures. The maximum ER of 22.3 dB was obtained, which was substantially high compared to previous reports. Our proposed modulators were sensitive to the polarization angle of incident light; therefore, the transmittance at resonant frequencies was increased while the polarization angle varied from 0° to 180°. These high-performance plasmonic modulators have emerging potential for the design of optical buffers, slow light devices, multistop band filters, integrated photonic circuits, and various optoelectronic systems.

High Q-Factor, High Contrast, and Multi-Band Optical Sensor Based on Plasmonic Square Bracket Dimer Metasurface.

A high-performance resonant metasurface is rather promising for diverse application areas such as optical sensing and filtering. Herein, a metal-insulator-metal (MIM) optical sensor with merits of a high quality-factor (Q-factor), multiple operating bands, and high spectrum contrast is proposed using plasmonic square bracket dimer metasurface. Due to the complex square bracket itself, a dimer structure of two oppositely placed square brackets, and metasurface array configuration, multiple kinds of mode coupling can be devised in the inner and outer elements within the metasurface, enabling four sensing channels with the sensitivities higher than 200 nm/RIU for refractive index sensing. Among them, the special sensing channel based on the reflection-type surface lattice resonance (SLR) mechanism has a full width at half maximum (FWHM) of only 2 nm, a high peak-to-dip signal contrast of 0.82, a high Q-factor of 548, and it can also behave as a good sensing channel for the thickness measurement of the deposition layer. The multi-band sensor can work normally in a large refractive index or thickness range, and the number of resonant channels can be further increased by simply breaking the structural symmetry or changing the polarization angle of incident light. Equipped with unique advantages, the suggested plasmonic metasurface has great potential in sensing, monitoring, filtering, and other applications.

Strong circular dichroism absorbers using chiral metamaterials with circular polarization

We designed and characterized a chiral metamaterial circularly polarized strong circular dichroism absorber with dynamic tuning capabilities using graphene. The synergistic combination of strong circular dichroism and perfect absorption, coupled with the tunability afforded by graphene, positions this absorber as a promising candidate for advanced electromagnetic applications. Employing a frequency-domain solver in electromagnetic simulation software, the impact of parameters such as the thickness of a metal U-ring, a silica dielectric layer, and the polarization angle of incident light on circular dichroism is systematically analyzed. Strong circular dichroism can be achieved by adjusting the misalignment angle of the metal U-ring, reaching a value as high as 0.91. At an incident angle of 60°, left-circularly polarized (LCP) light demonstrates outstanding wide-angle absorption performance, absorbing over 80% in the x-z plane and more than 70% in the y-z plane. Transitioning from circular to linear polarization and changing the tilt angle of the metal U-ring also achieves a 99.99% absorption peak at 1.33 THz. Moreover, in comparison to conventional absorbers, the structure presented in this study offers enhanced controllability of absorption performance through external voltage manipulation. This research not only refines the existing concepts but also introduces novel ideas for the development of tunable chiral optical devices.

A self-powered photodetector based on the C2P4 monolayer

In this paper, we proposed a self-powered photodetector driven by the photogalvanic effect based on the predicted C2P4 monolayer which has excellent electronic and mechanical properties. We focused on the tuning of photogalvanic effect by creating vacancy-defects and substitution doping using the DFT combined with Keldysh nonequilibrium green’s function formalism. We found that the photocurrents produced by the photogalvanic effect mainly show cosine dependence on the polarization angle of incident light, and the vacancy-defects and substitution-doping can increase the magnitude of photocurrents, corresponding to the enhancement of photogalvanic effect in the C2P4 photodetector. Moreover, the C2P4 photodetector possesses high extinction ratio, showing it is highly desirable for polarization detection applications. Our work reveals promising applications of the C2P4 monolayer for self-powered and low energy-consumption photogalvanic effect driven optoelectronics devices.

Chromatic Plasmonic Polarizer-Based Synapse for All-Optical Convolutional Neural Network.

Emerging memory devices have been demonstrated as artificial synapses for neural networks. However, the process of rewriting these synapses is often inefficient, in terms of hardware and energy usage. Herein, we present a novel surface plasmon resonance polarizer-based all-optical synapse for realizing convolutional filters and optical convolutional neural networks. The synaptic device comprises nanoscale crossed gold arrays with varying vertical and horizontal arms that respond strongly to the incident light's polarization angle. The presented synapse in an optical convolutional neural network achieved excellent performance in four different convolutional results for classifying the Modified National Institute of Standards and Technology (MNIST) handwritten digit data set. After training on 1,000 images, the network achieved a classification accuracy of over 98% when tested on a separate set of 10,000 images. This presents a promising approach for designing artificial neural networks with efficient hardware and energy consumption, low cost, and scalable fabrication.

Tunable Multiple Surface Plasmonic Bending Beams into Single One by Changing Incident Light Wavelength

Controllable surface plasmonic bending beams (SPBs) with propagating along bending curves have a wide range of applications in the fields of fiber sensors, optical trapping, and micro-nano manipulations. In terms of designing and optimizing controllable SPB generators, there is great significance in realizing conversion between multiple SPBs and single SPB without rebuilding metasurface structures. In this study, a SPB generator, composed of an X-shaped nanohole array, is proposed to realize conversion between multiple SPBs and a single one by changing the incident light wavelength. The Fabry–Pérot (F–P) resonance effect of SPPs in nanoholes and localized surface plasmonic (LSP) resonance of the nanohole are utilized to explain this conversion. It turns out that the relationship between the electric field intensities of SPBs and the polarization angle of incident light satisfies the sine distribution, which is consistent with dipole radiation theory. In addition, we also find that the electric field intensities of SPBs rely on the width, length, and angle of the X-shaped nanohole. These findings could help in designing and optimizing controllable and multi-functions SPBs converters.

All-optical polarization tuning based on an intensity-dependent nonlinear metasurface

Active control of light polarization at the nanoscale is essential for integrated photonic devices. Here, an all-optical approach is proposed to tune the polarization state of near-infrared light using a nonlinear metasurface. Based on the large intensity-dependent refractive index change of epsilon-near-zero (ENZ) materials, a phase difference between two orthogonal electric fields at ENZ wavelength can be continuously tuned in a range larger than 0.61π by varying the incident light power. The polarization state of the reflected light can thus be actively tuned from linear to circular state via an all-optical approach. Notably, abundant polarization states can be obtained by altering the polarization angle of incident light. The proposed all-optical approach is promising for tunable photonic functionalities of practical applications.

Generation of Bessel beams with tunable longitudinal electric and magnetic fields using an all-dielectric metasurface.

Optical beams with a pure longitudinally polarized field are of great interest for their unique properties and promising applications in various fields such as optical trapping and three-dimensional microscopy. Here, an all-dielectric metasurface is proposed to directly generate Bessel beams with tunable longitudinally polarized electric and magnetic fields under a simple incidence of linear polarization. Under the incidence of horizontal polarization, a Bessel beam with a pure longitudinally polarized electric field can be generated, which can be turned to a beam with a pure longitudinally polarized magnetic field when the incidence is switched to vertical polarization. More importantly, it is further demonstrated that the longitudinal components of the electric and magnetic fields can be accurately manipulated between zero and the maximum by simply changing the polarization angle of incident light. The simplicity and flexibility of this proposed metasurface may provide new possibilities in ultracompact photonic devices for optical trapping, optical storage, and related fields.

THz broadband and dual-channel perfect absorbers based on patterned graphene and vanadium dioxide metamaterials.

This paper proposes a novel and perfect absorber based on patterned graphene and vanadium dioxide hybrid metamaterial, which can not only achieve wide-band perfect absorption and dual-channel absorption in the terahertz band, but also realize their conversion by adjusting the temperature to control the metallic or insulating phase of VO2. Firstly, the absorption spectrum of the proposed structure is analyzed without graphene, where the absorption can reach as high as 100% at one frequency point (f = 5.956 THz) when VO2 is in the metal phase. What merits attention is that the addition of graphene above the structure enhances the almost 100% absorption from one frequency point (f = 5.956 THz) to a wide frequency band, in which the broadband width records 1.683 THz. Secondly, when VO2 is the insulating phase, the absorption of the metamaterial structure with graphene outperforms better, and two high absorption peaks are formed, logging 100% and 90.7% at f3 = 5.545 THz and f4 = 7.684 THz, respectively. Lastly, the adjustment of the Fermi level of graphene from 0.8 eV to 1.1 eV incurs an obvious blueshift of the absorption spectra, where an asynchronous optical switch can be achieved at fK1 = 5.782 THz and fK2 = 6.898 THz. Besides, the absorber exhibits polarization sensitivity at f3 = 5.545 THz, and polarization insensitivity at f4 = 7.684 THz with the shift in the polarization angle of incident light from 0° to 90°. Accordingly, this paper gives insights into the new method that increases the high absorption width, as well as the great potential in the multifunctional modulator.

Machine learning-assisted design of polarization-controlled dynamically switchable full-color metasurfaces.

Dynamic color tuning has significant application prospects in the fields of color display, steganography, and information encryption. However, most methods for color switching require external stimuli, which increases the structural complexity and hinders the applicability of front-end dynamic display technology. In this study, we propose polarization-controlled hybrid metal-dielectric metasurfaces to realize full-color display and dynamic color tuning by altering the polarization angle of incident light without changing the structure and properties of the material. A bidirectional neural network is trained to predict the colors of mixed metasurfaces and inversely design the geometric parameters for the desired colors, which is less dependent on design experience and reduces the computational cost. According to the color recognition ability of human eyes, the accuracy of color prediction realized in our study is 93.18% and that of inverse parameter design is 92.37%. This study presents a simple method for dynamic structural color tuning and accelerating the design of full-color metasurfaces, which can offer further insight into the design of color filters and promote photonics research.

Full color metasurface with high-transmission and omnidirectional characteristics

Nanostructured color filters particularly generated by surface plasmonic resonance of metal-dielectric nanostructures have been intensively studied in the past decades. However, the excitation of high-order scattering of surface plasmons and the intrinsic ohmic loss of metals hinder the generation of high efficiency and high color purity. In this study, we present a full color metasurface based on the concept of surface plasmons to produce the structural colors with high monochromaticity, low-loss, and wide gamut. Owing to the suppression of high-order scattering, the transmission spectra with narrow bandwidth and high efficiency could be formed to exhibit omnidirectional characteristic. Meanwhile, the dual- and multiple-resonance could be switched by changing the polarization angle of incident light. The proposed full color metasurface exhibits the enhancement of transmittance and increment of color monochromaticity. We expect that the proposed full color metasurface is promising for applications in real industries, such as information coding, optical data storage with high density, 2D/3D display, and so on.

Plasmonic Fano-like resonance in double-stacked graphene nanostrip arrays

We studied the plasmonic response in graphene nanostructures consisting of double-stacked graphene nanostrip arrays with a dielectric spacer on a substrate. The finite-difference time-domain simulations show that the Fano-like resonance in the mid-IR region can be generated due to the plasmonic coupling between the upper- and lower-layer graphene nanostrips. The resonance spectrum can also be effectively controlled by adjusting the geometrical parameters of the graphene system, such as the central position of the graphene nanostrips and the coupling distance between the upper- and lower-layer graphene nanostrips. Moreover, it was found that Fano-like resonance relies on the Fermi level of graphene and polarization angle of incident light, and the spectral response can be well analyzed by using the coupled-mode theory. These results would offer a new pathway to manipulate mid-IR light at the nanoscale and realize ultrasmall graphene functional devices.

Enhanced second-order nonlinearity and tunable plasmon induced transparency in noncoplanar Dirac semimetal system

Plasmon Induced Transparency (PIT) effect possesses the characteristics of sharp and pronounced spectral response and considerable group delay. In this work, a PIT system consists of two noncoplanar Dirac semimetal particles (DSPs) has been studied by finite-difference time-domain (FDTD) method. Tailoring of this PIT system can be achieved by structural parameters, Fermi energy (EF), refractive index (RI) of dielectric medium and polarization angle of incident light. Benefitted from its smaller particle size, the bandwidth of PIT window in this DSPs system is up to 3.94 THz, which is much broader than in bulk Dirac semimetal PIT system (about 0.36 THz). An efficient second order nonlinearity of this DSPs system is obtained for its intensive localized field, non-centrosymmetric structureunique and unique electromagnetic mode. The second-order nonlinear conversion efficiency in this system is up to 10−6 to 10−5 for its noncoplanar structure. This noncoplanar DSPs system can also achieve approximate linear light intensity modulation effect of its second harmonic waves (SHWs). This developed noncoplanar DSPs structure could provide guidance for the design of high integration Dirac semimetal THz devices.

Switching electromagnetically induced transparency in all-dielectric Si metamaterials with orthogonal double bright modes

Active control of electromagnetically induced transparency (EIT) in metamaterials promises tremendous potential applications. However, previously reported strategies most require sensitive materials as well as additional experimental apparatus, which are inconvenient for on-chip operation and restrain their implementations in fully integrated design. We propose a low-loss all-dielectric metamaterial with orthogonal double bright modes, which shows a narrowband transparency window at 950.05 nm with a high Q-factor of 2111. Just by varying the incident light polarization angle, an on-to-off in-situ EIT modulation without changing Q-factor is perfectly achieved, and the modulation depth can be up to 99.7%. Additionally, optical control of group delay with up to 36.22 ps is also demonstrated. This work provides a simple route to design chip-scale devices with optically dynamic controllability and finds fascinating applications in low-loss active slow light devices, optical switch and sensitive bio-sensing.

Anisotropic optical properties in a square quantum well wire under different polarizations of intense laser fields

In this paper, the polarization angle of intense laser field and incident light effects on the intersubband optical absorption and refractive index change in the square quantum well wire are investigated theoretically by Kramers–Henneberger approximation. It is found that the polarization angle of the intense laser field can influence the energy gap and exchange electronic configuration by breaking symmetry. Hence, the incident light polarization angle should be considered. The variation of optical absorption and refractive index change are given with different polarization-intense laser fields and probe light, which provides the possibility of designing various polarization-sensitive devices.

Whispering-gallery mode resonance-assisted plasmonic sensing and switching in subwavelength nanostructures

Whispering-gallery modes (WGMs), confining the resonant photons in nanoscale volumes, have been known to exhibit high-quality factor and sensitivity for electromagnetic waves in the field of nanophotonics. Here, we numerically demonstrate that a metasurface, which consists of periodic arrays with concentrically hybrid rectangular-slot (RS) and circular-ring-aperture (CRA) unit cells, supports polarization-dependent plasmonic sensing and switching in the visible and near-infrared regions. In particular, it is shown that the magnetic plasmon-induced transparency (PIT) effect arises from the coupling between a wideband WGM resonance and a narrowband magnetic dipole resonance mode in the hybrid metasurface. It is of great interest to find that the resonance mode broadening and mode shift sensing can be realized by varying the polarization angle of incident light and the length of the RS structure, respectively. Moreover, a novel and easy-fabricated plasmonic switching can be implemented in the visible and near-infrared regions. By changing the inner radius of the CRA structure, we reveal that the operating wavelength of the plasmonic switching can be extended to the telecom O- or E-band with an optimal ON/OFF ratio being 18.35 dB. Our results provide a path toward designing compact and tunable PIT device and could expand the application range of subwavelength nanostructures to the realm of optical communications and information process.

Zero-bias mid-infrared graphene photodetectors with bulk photoresponse and calibration-free polarization detection

Bulk photovoltaic effect (BPVE), featuring polarization-dependent uniform photoresponse at zero external bias, holds potential for exceeding the Shockley-Queisser limit in the efficiency of existing opto-electronic devices. However, the implementation of BPVE has been limited to the naturally existing materials with broken inversion symmetry, such as ferroelectrics, which suffer low efficiencies. Here, we propose metasurface-mediated graphene photodetectors with cascaded polarization-sensitive photoresponse under uniform illumination, mimicking an artificial BPVE. With the assistance of non-centrosymmetric metallic nanoantennas, the hot photocarriers in graphene gain a momentum upon their excitation and form a shift current which is nonlocal and directional. Thereafter, we demonstrate zero-bias uncooled mid-infrared photodetectors with three orders higher responsivity than conventional BPVE and a noise equivalent power of 0.12 nW Hz−1/2. Besides, we observe a vectorial photoresponse which allows us to detect the polarization angle of incident light with a single device. Our strategy opens up alternative possibilities for scalable, low-cost, multifunctional infrared photodetectors.

Bi-functional switchable broadband terahertz polarization converter based on a hybrid graphene-metal metasurface.

In this letter, we have proposed a bi-functional switchable broadband polarization converter based on the hybrid graphene-metal metasurface. Turning the bias voltage to change Fermi level Ef from 0 to 1.0 eV, the metasurface can switch between quarter-wave plate (QWP) and half-wave plate (HWP) in the frequency band 1.38-1.72 THz. Besides, the metasurface simultaneously works as a broadband QWP and HWP in different frequency range when Ef = 1.0 eV. In addition, when Ef is in the range of 0.3 eV-0.6 eV, the metasurface can work as bi-functional broadband QWP in different frequencies as well. The physical mechanism of the bi-functional polarization converter can be explained by the electric field amplitude distributions. What's more, we find that the metasurface can work well with a tolerance to the incident light polarization angle of about ± 12.5°, which can also change the converted wave from RHCP to LHCP with the incident polarization angle change of 90°. The hybrid metasurface with the advantages of switchable bi-functions, wide operating bandwidth, and ultra-thin thickness, may achieve potential applications in tunable devices for terahertz communications.

Optical properties of PMMA inverse opal structures with anisotropic geometries by stretching

The fabrication of three-dimensional periodic microstructures with strong anisotropic geometries is important for nanophotonic devices including photonic crystals and hyperbolic metamaterials. In this study, a simple method using self-organizing colloidal inverse opals of PMMA with directional tensile deformation by stretching was successfully constructed in the temperature range 100 °C–115 °C. Reflection spectroscopy was used for investigating the photonic bandgap of the PMMA inverse opal with anisotropic geometries in anisotropic different extents. The wavelengths of the photonic band gap were related to both the length of the pores in long-axis and short-axis of pores of the inverse opals. The wavelength changes of the photonic band gap significantly affected by the length variation in the short-axis. The anisotropic optical properties were also observed when Ag and Pt were deposited onto the top surface or conformally coated onto the interior interfaces of the anisotropic inverse opals. The structures with higher anisotropic ratios showed stronger variations in the wavelengths of the reflection valleys according to the surface plasmonic polarizations and cut-off frequencies with varying polarization angles of incident light. Moreover, the PMMA inverse opals conformally coated with metals presented indefinite dielectric properties in the visible or near-infrared wavelength region.