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Metamaterials|13 Article(s)
Generalization of the effects of high Q for metamaterials
Raphael Tsu, and Michael A. Fiddy
We revisit the electrodynamics of resonant high-Q interactions in atomic systems with a view to gaining insights into the design of meta-atoms and hence bulk metamaterials with profoundly different electromagnetic responses. The relevance of phase coherence and nonlinearity in charged systems is emphasized, as is the need to take care over defining how one specifies effective boundaries and cavities that ultimately determine light–matter interactions. Radically new material properties become apparent once one designs organized clusters of small numbers of atoms or meta-atoms for which the usually applied random phase approximation (RPA) does not apply. The RPA relies on averages in sufficiently large volumes consisting of large numbers of interacting systems, while our model assumes a small volume with averages in time, i.e., ergodicity. New meaning is given to the concept of effective and practically useful constitutive parameters, based on this very fundamental point of view, which is important to metamaterials. We revisit the electrodynamics of resonant high-Q interactions in atomic systems with a view to gaining insights into the design of meta-atoms and hence bulk metamaterials with profoundly different electromagnetic responses. The relevance of phase coherence and nonlinearity in charged systems is emphasized, as is the need to take care over defining how one specifies effective boundaries and cavities that ultimately determine light–matter interactions. Radically new material properties become apparent once one designs organized clusters of small numbers of atoms or meta-atoms for which the usually applied random phase approximation (RPA) does not apply. The RPA relies on averages in sufficiently large volumes consisting of large numbers of interacting systems, while our model assumes a small volume with averages in time, i.e., ergodicity. New meaning is given to the concept of effective and practically useful constitutive parameters, based on this very fundamental point of view, which is important to metamaterials.
Photonics Research
- Publication Date: Jul. 19, 2013
- Vol. 1, Issue 2, 02000077 (2013)
Ultra-thin, planar, broadband, dual-polarity plasmonic metalens
Wei Wang, Zhongyi Guo, Rongzhen Li, Jingran Zhang, Yi Liu, Xinshun Wang, and Shiliang Qu
An ultrathin, planar, broadband metalens composed of metal rectangular split-ring resonators (MRSRRs) has been designed, which shows dual-polarity characteristics for different types of circularly polarized (CP) light incidence. The designed metalens can be considered as the focusing lens and the diverging lens under left-handed CP and right-handed CP light incidence, respectively. The phase discontinuity of the cross-polarized transmission light is produced by optical-axis rotation through modulating two arms’ lengths of the MRSRR. The MRSRR metalens possesses a wavelength-controllable focal length and a relatively larger chromatic aberration compared with the conventional lenses. And the focal length changes from 9 to 7 μm with incident wavelength from 740 to 950 nm. The dual-polarity flat metalens opens a door for new applications of phase discontinuity devices, and it will promote the fabricating capability of on-chip or fiber-embedded optical devices. An ultrathin, planar, broadband metalens composed of metal rectangular split-ring resonators (MRSRRs) has been designed, which shows dual-polarity characteristics for different types of circularly polarized (CP) light incidence. The designed metalens can be considered as the focusing lens and the diverging lens under left-handed CP and right-handed CP light incidence, respectively. The phase discontinuity of the cross-polarized transmission light is produced by optical-axis rotation through modulating two arms’ lengths of the MRSRR. The MRSRR metalens possesses a wavelength-controllable focal length and a relatively larger chromatic aberration compared with the conventional lenses. And the focal length changes from 9 to 7 μm with incident wavelength from 740 to 950 nm. The dual-polarity flat metalens opens a door for new applications of phase discontinuity devices, and it will promote the fabricating capability of on-chip or fiber-embedded optical devices.
Photonics Research
- Publication Date: Apr. 09, 2015
- Vol. 3, Issue 3, 03000068 (2015)
Complex band structures of 1D anisotropic graphene photonic crystal
Limei Qi, and Chang Liu
The complex band structures of a 1D anisotropic graphene photonic crystal are investigated, and the dispersion relations are confirmed using the transfer matrix method and simulation of commercial software. It is found that the result of using effective medium theory can fit the derived dispersion curves in the low wave vector. Transmission, absorption, and reflection at oblique incident angles are studied for the structure, respectively. Omni-gaps exist for angles as high as 80° for two polarizations. Physical mechanisms of the tunable dispersion and transmission are explained by the permittivity of graphene and the effective permittivity of the multilayer structure. The complex band structures of a 1D anisotropic graphene photonic crystal are investigated, and the dispersion relations are confirmed using the transfer matrix method and simulation of commercial software. It is found that the result of using effective medium theory can fit the derived dispersion curves in the low wave vector. Transmission, absorption, and reflection at oblique incident angles are studied for the structure, respectively. Omni-gaps exist for angles as high as 80° for two polarizations. Physical mechanisms of the tunable dispersion and transmission are explained by the permittivity of graphene and the effective permittivity of the multilayer structure.
Photonics Research
- Publication Date: Sep. 05, 2017
- Vol. 5, Issue 6, 06000543 (2017)
Tunable and multichannel terahertz perfect absorber due to Tamm surface plasmons with graphene
Xi Wang, Xing Jiang, Qi You, Jun Guo, Xiaoyu Dai, and Yuanjiang Xiang
In this paper, we have shown that perfect absorption at terahertz frequencies can be achieved by using a composite structure where graphene is coated on one-dimensional photonic crystal (1DPC) separated by a dielectric. Due to the excitation of optical Tamm states (OTSs) at the interface between the graphene and 1DPC, a strong absorption phenomenon occurs induced by the coupling of the incident light and OTSs. Although the perfect absorption produced by a metal–distributed Bragg reflector structure has been researched extensively, it is generally at a fixed frequency and not tunable. Here, we show that the perfect absorption at terahertz frequency not only can be tuned to different frequencies but also exhibits a high absorption over a wide angle range. In addition, the absorption of the proposed structure is insensitive to the polarization, and multichannel absorption can be realized by controlling the thickness of the top layer. In this paper, we have shown that perfect absorption at terahertz frequencies can be achieved by using a composite structure where graphene is coated on one-dimensional photonic crystal (1DPC) separated by a dielectric. Due to the excitation of optical Tamm states (OTSs) at the interface between the graphene and 1DPC, a strong absorption phenomenon occurs induced by the coupling of the incident light and OTSs. Although the perfect absorption produced by a metal–distributed Bragg reflector structure has been researched extensively, it is generally at a fixed frequency and not tunable. Here, we show that the perfect absorption at terahertz frequency not only can be tuned to different frequencies but also exhibits a high absorption over a wide angle range. In addition, the absorption of the proposed structure is insensitive to the polarization, and multichannel absorption can be realized by controlling the thickness of the top layer.
Photonics Research
- Publication Date: Sep. 11, 2017
- Vol. 5, Issue 6, 06000536 (2017)
Ultrasensitive terahertz metamaterial sensor based on vertical split ring resonators
Wei Wang, Fengping Yan, Siyu Tan, Hong Zhou, and Yafei Hou
An ultrasensitive metamaterial sensor based on double-slot vertical split ring resonators (DVSRRs) is designed and numerically calculated in the terahertz frequency. This DVSRR design produces a fundament LC resonance with a quality factor of about 20 when the incidence magnetic field component normal to the DVSRR array. The resonant characteristics and sensing performance of the DVSRR array design are systematically analyzed employing a contrast method among three similar vertical split ring resonator (SRRs) structures. The research results show that the elimination of bianisotropy, induced by the structural symmetry of the DVSRR design, helps to achieve LC resonance of a high quality factor. Lifting the SRRs up from the substrate sharply reduces the dielectric loss introduced by the substrate. All these factors jointly result in superior sensitivity of the DVSRR to the attributes of analytes. The maximum refractive index sensitivity is 788 GHz/RIU or 1.04×105 nm/RIU. Also, the DVSRR sensor maintains its superior sensing performance for fabrication tolerance ranging from ?4% to 4% and wide range incidence angles up to 50° under both TE and TM illuminations. An ultrasensitive metamaterial sensor based on double-slot vertical split ring resonators (DVSRRs) is designed and numerically calculated in the terahertz frequency. This DVSRR design produces a fundament LC resonance with a quality factor of about 20 when the incidence magnetic field component normal to the DVSRR array. The resonant characteristics and sensing performance of the DVSRR array design are systematically analyzed employing a contrast method among three similar vertical split ring resonator (SRRs) structures. The research results show that the elimination of bianisotropy, induced by the structural symmetry of the DVSRR design, helps to achieve LC resonance of a high quality factor. Lifting the SRRs up from the substrate sharply reduces the dielectric loss introduced by the substrate. All these factors jointly result in superior sensitivity of the DVSRR to the attributes of analytes. The maximum refractive index sensitivity is 788 GHz/RIU or 1.04×105 nm/RIU. Also, the DVSRR sensor maintains its superior sensing performance for fabrication tolerance ranging from ?4% to 4% and wide range incidence angles up to 50° under both TE and TM illuminations.
Photonics Research
- Publication Date: Sep. 15, 2017
- Vol. 5, Issue 6, 06000571 (2017)
Theoretical study of tunable chirality from graphene integrated achiral metasurfaces
Tun Cao, Yang Li, Xinyu Zhang, and Yang Zou
Control of chirality using metamaterials plays a critical role in a diverse set of advanced photonics applications, such as polarization control, bio-sensing, and polarization-sensitive imaging devices. However, this poses a major challenge, as it primarily involves the geometrical reconfiguration of metamolecules that cannot be adjusted dynamically. Real-world applications require active tuning of the chirality, which can easily manipulate the magnitude, handedness, and spectral range of chiroptical response. Here, enabled by graphene, we theoretically reveal a tunable/switchable achiral metasurface in the near-infrared region. In the model, the achiral metasurface consists of an array of circular holes embedded through a metal/dielectric/metal trilayer incorporated with the graphene sheet, where holes occupy the sites of a rectangular lattice. Circular conversion dichroism (CCD) originates from the mutual orientation between the achiral metasurface and oblique incident wave. The achiral metasurface possesses dual-band sharp features in the CCD spectra, which are tuned over a broad bandwidth by electrically modulating the graphene’s Fermi level. By selecting aluminium as the metal materials, we numerically achieved strong CCD and considerably reduced materials costs with our nanostructures compared with the typically used noble metals such as gold and silver. Control of chirality using metamaterials plays a critical role in a diverse set of advanced photonics applications, such as polarization control, bio-sensing, and polarization-sensitive imaging devices. However, this poses a major challenge, as it primarily involves the geometrical reconfiguration of metamolecules that cannot be adjusted dynamically. Real-world applications require active tuning of the chirality, which can easily manipulate the magnitude, handedness, and spectral range of chiroptical response. Here, enabled by graphene, we theoretically reveal a tunable/switchable achiral metasurface in the near-infrared region. In the model, the achiral metasurface consists of an array of circular holes embedded through a metal/dielectric/metal trilayer incorporated with the graphene sheet, where holes occupy the sites of a rectangular lattice. Circular conversion dichroism (CCD) originates from the mutual orientation between the achiral metasurface and oblique incident wave. The achiral metasurface possesses dual-band sharp features in the CCD spectra, which are tuned over a broad bandwidth by electrically modulating the graphene’s Fermi level. By selecting aluminium as the metal materials, we numerically achieved strong CCD and considerably reduced materials costs with our nanostructures compared with the typically used noble metals such as gold and silver.
Photonics Research
- Publication Date: Jul. 31, 2017
- Vol. 5, Issue 5, 05000441 (2017)
Tuning the metal filling fraction in metal-insulator-metal ultra-broadband perfect absorbers to maximize the absorption bandwidth
Amir Ghobadi, Hodjat Hajian, Alireza Rahimi Rashed, Bayram Butun, and Ekmel Ozbay
In this paper, we propose a methodology to maximize the absorption bandwidth of a metal-insulator-metal (MIM) based absorber. The proposed structure is made of a Cr-Al2O3-Cr multilayer design. At the initial step, the optimum MIM planar design is fabricated and optically characterized. The results show absorption above 0.9 from 400 nm to 850 nm. Afterward, the transfer matrix method is used to find the optimal condition for the perfect light absorption in an ultra-broadband frequency range. This modeling approach predicts that changing the filling fraction of the top Cr layer can extend light absorption toward longer wavelengths. We experimentally proved that the use of proper top Cr thickness and annealing temperature leads to a nearly perfect light absorption from 400 nm to 1150 nm, which is much broader than that of a planar design. Therefore, while keeping the overall process lithography-free, the absorption functionality of the design can be significantly improved. The results presented here can serve as a beacon for future performance-enhanced multilayer designs where a simple fabrication step can boost the overall device response without changing its overall thickness and fabrication simplicity. In this paper, we propose a methodology to maximize the absorption bandwidth of a metal-insulator-metal (MIM) based absorber. The proposed structure is made of a Cr-Al2O3-Cr multilayer design. At the initial step, the optimum MIM planar design is fabricated and optically characterized. The results show absorption above 0.9 from 400 nm to 850 nm. Afterward, the transfer matrix method is used to find the optimal condition for the perfect light absorption in an ultra-broadband frequency range. This modeling approach predicts that changing the filling fraction of the top Cr layer can extend light absorption toward longer wavelengths. We experimentally proved that the use of proper top Cr thickness and annealing temperature leads to a nearly perfect light absorption from 400 nm to 1150 nm, which is much broader than that of a planar design. Therefore, while keeping the overall process lithography-free, the absorption functionality of the design can be significantly improved. The results presented here can serve as a beacon for future performance-enhanced multilayer designs where a simple fabrication step can boost the overall device response without changing its overall thickness and fabrication simplicity.
Photonics Research
- Publication Date: Feb. 12, 2018
- Vol. 6, Issue 3, 03000168 (2018)
High-efficiency broadband polarization-independent superscatterer using conformal metasurfaces
He-Xiu Xu, Shiwei Tang, Chen Sun, Lianlin Li, Haiwen Liu, Xinmi Yang, Fang Yuan, and Yunming Sun
Safe detection of an arbitrarily shaped platform is critical for survivability, rescue, or navigation safety in a remote region. Metasurfaces afford great potential due to their strong electromagnetic (EM) wave control. However, studies have mainly focused on the physics and design of metasurfaces on planar plates, which does not satisfy the current requirements of aerodynamics and aesthetics. Herein, we propose a sophisticated strategy to design a metasurface that can wrap over arbitrarily shaped objects with moderate curvature on which optical aberrations are commonly introduced. By designing each meta-atom on the basis of the required position and phase compensation, exact EM wavefronts are restored. For verification, several conformal metasurfaces were designed and numerically studied on metallic cylinders at the microwave spectrum. A proof-of-concept device is fabricated and is experimentally characterized. The results demonstrate the availability of the desirable dual-beam superscatterer with strong backscattering enhancement toward two directions, thus indicating that the distortions induced by an arbitrary platform can be efficiently corrected. Our method affords an efficient alternative for designing high-performance multifunctional optoelectronic devices equipped on a moderately curved platform. Safe detection of an arbitrarily shaped platform is critical for survivability, rescue, or navigation safety in a remote region. Metasurfaces afford great potential due to their strong electromagnetic (EM) wave control. However, studies have mainly focused on the physics and design of metasurfaces on planar plates, which does not satisfy the current requirements of aerodynamics and aesthetics. Herein, we propose a sophisticated strategy to design a metasurface that can wrap over arbitrarily shaped objects with moderate curvature on which optical aberrations are commonly introduced. By designing each meta-atom on the basis of the required position and phase compensation, exact EM wavefronts are restored. For verification, several conformal metasurfaces were designed and numerically studied on metallic cylinders at the microwave spectrum. A proof-of-concept device is fabricated and is experimentally characterized. The results demonstrate the availability of the desirable dual-beam superscatterer with strong backscattering enhancement toward two directions, thus indicating that the distortions induced by an arbitrary platform can be efficiently corrected. Our method affords an efficient alternative for designing high-performance multifunctional optoelectronic devices equipped on a moderately curved platform.
Photonics Research
- Publication Date: Jul. 09, 2018
- Vol. 6, Issue 8, 08000782 (2018)
Label-free sensing of ultralow-weight molecules with all-dielectric metasurfaces supporting bound states in the continuum
Silvia Romano, Gianluigi Zito, Stefania Torino, Giuseppe Calafiore, Erika Penzo, Giuseppe Coppola, Stefano Cabrini, Ivo Rendina, and Vito Mocella
The realization of an efficient optical sensor based on a photonic crystal metasurface supporting bound states in the continuum is reported. Liquids with different refractive indices, ranging from 1.4000 to 1.4480, are infiltrated in a microfluidic chamber bonded to the sensing dielectric metasurface. A bulk liquid sensitivity of 178 nm/RIU is achieved, while a Q-factor of about 2000 gives a sensor figure of merit up to 445 in air at both visible and infrared excitations. Furthermore, the detection of ultralow-molecular-weight (186 Da) molecules is demonstrated with a record resonance shift of 6 nm per less than a 1 nm thick single molecular layer. The system exploits a normal-to-the-surface optical launching scheme, with excellent interrogation stability and demonstrates alignment-free performances, overcoming the limits of standard photonic crystals and plasmonic resonant configurations. The realization of an efficient optical sensor based on a photonic crystal metasurface supporting bound states in the continuum is reported. Liquids with different refractive indices, ranging from 1.4000 to 1.4480, are infiltrated in a microfluidic chamber bonded to the sensing dielectric metasurface. A bulk liquid sensitivity of 178 nm/RIU is achieved, while a Q-factor of about 2000 gives a sensor figure of merit up to 445 in air at both visible and infrared excitations. Furthermore, the detection of ultralow-molecular-weight (186 Da) molecules is demonstrated with a record resonance shift of 6 nm per less than a 1 nm thick single molecular layer. The system exploits a normal-to-the-surface optical launching scheme, with excellent interrogation stability and demonstrates alignment-free performances, overcoming the limits of standard photonic crystals and plasmonic resonant configurations.
Photonics Research
- Publication Date: Jun. 21, 2018
- Vol. 6, Issue 7, 07000726 (2018)
Tunable spin splitting of Laguerre–Gaussian beams in graphene metamaterials
Wenguo Zhu, Mengjiang Jiang, Heyuan Guan, Jianhui Yu, Huihui Lu, Jun Zhang, and Zhe Chen
Optical spin splitting has attracted significant attention owing to its potential applications in quantum information and precision metrology. However, it is typically small and cannot be controlled efficiently. Here, we enhance the spin splitting by transmitting higher-order Laguerre–Gaussian (LG) beams through graphene metamaterial slabs. The interaction between LG beams and metamaterial results in an orbital-angular-momentum- (OAM) dependent spin splitting. The upper bound of the OAM-dependent spin splitting is found, which varies with the incident OAM and beam waist. Moreover, the spin splitting can be flexibly tuned by modulating the Fermi energy of the graphene sheets. This tunable spin splitting has potential applications in the development of spin-based applications and the manipulation of mid-infrared waves. Optical spin splitting has attracted significant attention owing to its potential applications in quantum information and precision metrology. However, it is typically small and cannot be controlled efficiently. Here, we enhance the spin splitting by transmitting higher-order Laguerre–Gaussian (LG) beams through graphene metamaterial slabs. The interaction between LG beams and metamaterial results in an orbital-angular-momentum- (OAM) dependent spin splitting. The upper bound of the OAM-dependent spin splitting is found, which varies with the incident OAM and beam waist. Moreover, the spin splitting can be flexibly tuned by modulating the Fermi energy of the graphene sheets. This tunable spin splitting has potential applications in the development of spin-based applications and the manipulation of mid-infrared waves.
Photonics Research
- Publication Date: Oct. 07, 2017
- Vol. 5, Issue 6, 06000684 (2017)
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