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Plasmonics and Metamaterials|11 Article(s)
Tunable terahertz absorber based on transparent and flexible metamaterial
Junyu Xiao, Ruiwen Xiao, Rongxuan Zhang, Zhixiong Shen, Wei Hu, Lei Wang, and Yanqing Lu
We demonstrate a tunable terahertz (THz) absorber based on an indium tin oxide (ITO) metamaterial. The upper ITO cross-shaped metasurface with different arm lengths is fabricated by direct femtosecond laser etching. The thickness of the middle dielectric layer is only 60 μm, which makes the absorber very transparent and flexible. The experimental results show that the THz resonant peaks have a high performance near 1 THz. By setting spacers of different thicknesses between the middle layer and the ITO mirror, a new type of tunable THz absorber is proposed. Its absorption peak frequency can be continuously adjusted from 0.92 to 1.04 THz between TE and TM polarization. This transparent THz metamaterial absorber is expected to be widely used in THz imaging, sensing, and biological detection. We demonstrate a tunable terahertz (THz) absorber based on an indium tin oxide (ITO) metamaterial. The upper ITO cross-shaped metasurface with different arm lengths is fabricated by direct femtosecond laser etching. The thickness of the middle dielectric layer is only 60 μm, which makes the absorber very transparent and flexible. The experimental results show that the THz resonant peaks have a high performance near 1 THz. By setting spacers of different thicknesses between the middle layer and the ITO mirror, a new type of tunable THz absorber is proposed. Its absorption peak frequency can be continuously adjusted from 0.92 to 1.04 THz between TE and TM polarization. This transparent THz metamaterial absorber is expected to be widely used in THz imaging, sensing, and biological detection.
Chinese Optics Letters
- Publication Date: Sep. 10, 2020
- Vol. 18, Issue 9, 092403 (2020)
Active formatting modulation of electromagnetically induced transparency in metamaterials|Editors' Pick
Hao Sun, Yuhua Tang, Yuze Hu, Jie You, Hengzhu Liu, and Xin Zheng
We experimentally demonstrate for the first time an active all-optical ultrafast modulation of electromagnetically induced transparency-like effect in a hybrid device of sapphire/Si/metamaterial. From numerical simulations, it can be deducted that the tuning process is attributed to the coupling between the dark mode existing in split-ring resonators and the bright mode existing in cut wire resonators. The transmission amplitude modulation is accompanied by the slow-light effect. In addition, the ultrafast formation process is measured to be as fast as 2 ps. This work should make an important contribution to novel chip-scale photonic devices and terahertz communications. We experimentally demonstrate for the first time an active all-optical ultrafast modulation of electromagnetically induced transparency-like effect in a hybrid device of sapphire/Si/metamaterial. From numerical simulations, it can be deducted that the tuning process is attributed to the coupling between the dark mode existing in split-ring resonators and the bright mode existing in cut wire resonators. The transmission amplitude modulation is accompanied by the slow-light effect. In addition, the ultrafast formation process is measured to be as fast as 2 ps. This work should make an important contribution to novel chip-scale photonic devices and terahertz communications.
Chinese Optics Letters
- Publication Date: Sep. 10, 2020
- Vol. 18, Issue 9, 092402 (2020)
Plasmonic Luneburg lens and plasmonic nano-coupler
Lei Zhang, Lin Wang, Yanqing Wu, and Renzhong Tai
In a single nanoscale device, surface plasmon polaritons (SPPs) have potential to match the different length scales associated with photonics and electronics. In this Letter, we propose an accurate design of a plasmonic metasurface Luneburg lens (PMLL) accommodating SPPs. The simulations indicate that the full width at half-maximum is 0.42 μm, and the focus efficiency is 78%. The characters of a PMLL have robustness to manufacturing errors. The PMLL is applied in a 10 μm long compact coupler model, which couples the SPPs to the 40 nm wide output waveguide. The couple efficiency is higher than that of a conventional taper coupler in a broad bandwidth. The design is compatible with standard lithography technology. In a single nanoscale device, surface plasmon polaritons (SPPs) have potential to match the different length scales associated with photonics and electronics. In this Letter, we propose an accurate design of a plasmonic metasurface Luneburg lens (PMLL) accommodating SPPs. The simulations indicate that the full width at half-maximum is 0.42 μm, and the focus efficiency is 78%. The characters of a PMLL have robustness to manufacturing errors. The PMLL is applied in a 10 μm long compact coupler model, which couples the SPPs to the 40 nm wide output waveguide. The couple efficiency is higher than that of a conventional taper coupler in a broad bandwidth. The design is compatible with standard lithography technology.
Chinese Optics Letters
- Publication Date: Sep. 10, 2020
- Vol. 18, Issue 9, 092401 (2020)
Chromatic dispersion manipulation based on metasurface devices in the mid-infrared region
Lin Li, Quan Yuan, Run Chen, Xiujuan Zou, Wenbo Zang, Tianyue Li, Gaige Zheng, Shuming Wang, Zhenlin Wang, and Shining Zhu
The chromatic aberration of metasurfaces limits their application. How to cancel or utilize the large chromatic dispersion of metasurfaces becomes an important issue. Here, we design Si-based metasurfaces to realize flexible chromatic dispersion manipulation in mid-infrared region. We demonstrate the broadband achromatic metalens and achromatic gradient metasurface to cancel the chromatic aberration over a continuous bandwidth (8–12 μm). In contrast, the metalens and gradient metasurface with enhanced chromatic dispersion have also been realized, where the focal length and deflection angle with different wavelengths vary more significantly than the conventional devices designed with geometric phase. These demonstrations indicate promising potential applications. The chromatic aberration of metasurfaces limits their application. How to cancel or utilize the large chromatic dispersion of metasurfaces becomes an important issue. Here, we design Si-based metasurfaces to realize flexible chromatic dispersion manipulation in mid-infrared region. We demonstrate the broadband achromatic metalens and achromatic gradient metasurface to cancel the chromatic aberration over a continuous bandwidth (8–12 μm). In contrast, the metalens and gradient metasurface with enhanced chromatic dispersion have also been realized, where the focal length and deflection angle with different wavelengths vary more significantly than the conventional devices designed with geometric phase. These demonstrations indicate promising potential applications.
Chinese Optics Letters
- Publication Date: Aug. 10, 2020
- Vol. 18, Issue 8, 082401 (2020)
Effective medium theory of checkboard structures in the long-wavelength limit
Zhanlei Hao, Yawen Zhuang, Ying Chen, Yineng Liu, and Huanyang Chen
Effective medium theory is a powerful tool to solve various problems for achieving multifarious functionalities and applications. In this article, we present a concise empirical formula about effective permittivity of checkboard structures for different directions. To verify our empirical formula, we perform simulations of checkboard periodic structures in squares, rectangles, and sectors in two dimensions. Our results show that the formula is valid in a large range of parameters. This work provides a new way to understand and design composite materials, which might lead to further optical applications in transformation optics. Effective medium theory is a powerful tool to solve various problems for achieving multifarious functionalities and applications. In this article, we present a concise empirical formula about effective permittivity of checkboard structures for different directions. To verify our empirical formula, we perform simulations of checkboard periodic structures in squares, rectangles, and sectors in two dimensions. Our results show that the formula is valid in a large range of parameters. This work provides a new way to understand and design composite materials, which might lead to further optical applications in transformation optics.
Chinese Optics Letters
- Publication Date: Jul. 10, 2020
- Vol. 18, Issue 7, 072401 (2020)
Morse lens [Invited]|Editors' Pick
Huanyang Chen, and Wen Xiao
In this Letter, we find that Morse potential (proposed about 90 years ago) could be connected to Coulomb potential (or Newton potential) and harmonic potential (or Hooke potential) by conformal mappings. We thereby design a new conformal lens from Morse potential, Eaton lens, and Luneburg lens and propose a series of generalized Eaton/Luneburg lenses. We find that this Morse lens is a perfect self-focusing asymmetric lens that differs from a Mikaelian lens. Our theory provides a new insight to Morse potential and other traditional potentials, and revisits their classical applications on designing lenses. In this Letter, we find that Morse potential (proposed about 90 years ago) could be connected to Coulomb potential (or Newton potential) and harmonic potential (or Hooke potential) by conformal mappings. We thereby design a new conformal lens from Morse potential, Eaton lens, and Luneburg lens and propose a series of generalized Eaton/Luneburg lenses. We find that this Morse lens is a perfect self-focusing asymmetric lens that differs from a Mikaelian lens. Our theory provides a new insight to Morse potential and other traditional potentials, and revisits their classical applications on designing lenses.
Chinese Optics Letters
- Publication Date: Jun. 10, 2020
- Vol. 18, Issue 6, 062403 (2020)
Tunable beam deflection based on plasmonic resonators mounted freestanding thermoresponsive hydrogel
Ata Ur Rahman Khalid, Juan Liu, Naeem Ullah, and Shiqi Jia
We propose and numerically demonstrate a dynamic beam deflector based on plasmonic resonator loaded thermoresponsive freestanding hydrogel that swells and collapses in water by temperature. For this purpose, we utilize four-step phase gradients mounted on freestanding hydrated hydrogel. For normal incidence, linearly orthogonal light deflects to 19.44° in the collapsed state and 14.40° in the swollen state of hydrogel. Furthermore, the light deflects at a third angle of 12.29° when the solvent changes from water to ethanol. It is expected that our metadesign will provide a platform for dynamic holography, active lensing, data storage, and anticounterfeiting. We propose and numerically demonstrate a dynamic beam deflector based on plasmonic resonator loaded thermoresponsive freestanding hydrogel that swells and collapses in water by temperature. For this purpose, we utilize four-step phase gradients mounted on freestanding hydrated hydrogel. For normal incidence, linearly orthogonal light deflects to 19.44° in the collapsed state and 14.40° in the swollen state of hydrogel. Furthermore, the light deflects at a third angle of 12.29° when the solvent changes from water to ethanol. It is expected that our metadesign will provide a platform for dynamic holography, active lensing, data storage, and anticounterfeiting.
Chinese Optics Letters
- Publication Date: Jun. 10, 2020
- Vol. 18, Issue 6, 062402 (2020)
Advancements in high refractive index media: from quantum coherence in atomic systems to deep sub-wavelength coupling in metamaterials [Invited]
Leena Singh, and Weili Zhang
Refractive index enhancement is crucial in the fields of lithography, imaging, optical communications, solar devices, and many more. We present a review of advancements in the process of designing high refractive index metamaterials, starting from quantum coupling and photonic bandgap materials to metamaterials utilizing deep subwavelength coupling to achieve ever-high values of refractive index. A particular attention is given to experimentally verified schemes in engineering a high index of refraction. The understanding of the evolution of material design from intrinsic electronic states manipulation to meta-atoms design is not only fascinating but also a prerequisite to developing successful devices and applications. Refractive index enhancement is crucial in the fields of lithography, imaging, optical communications, solar devices, and many more. We present a review of advancements in the process of designing high refractive index metamaterials, starting from quantum coupling and photonic bandgap materials to metamaterials utilizing deep subwavelength coupling to achieve ever-high values of refractive index. A particular attention is given to experimentally verified schemes in engineering a high index of refraction. The understanding of the evolution of material design from intrinsic electronic states manipulation to meta-atoms design is not only fascinating but also a prerequisite to developing successful devices and applications.
Chinese Optics Letters
- Publication Date: Jun. 10, 2020
- Vol. 18, Issue 6, 062401 (2020)
A polarization-insensitive fishnet/spacer/mirror plasmonic absorber for hot electron photodetection application
Zhiqiang Yang, Kang Du, Wending Zhang, Soojin Chua, and Ting Mei
A polarization-insensitive plasmonic absorber is designed consisting of Au fishnet structures on a TiO2 spacer/Ag mirror. The fishnet structures excite localized surface plasmon and generate hot electrons from the absorbed photons, while the TiO2 layer induces Fabry–Perot resonance, and the Ag mirror acts as a back reflector. Through optimizing the TiO2 layer thickness, numerical simulation shows that 97% of the incident light is absorbed in the Au layer. The maximum responsivity and external quantum efficiency of the device can approach 5 mA/W and ～1%, respectively, at the wavelength of 700 nm. A polarization-insensitive plasmonic absorber is designed consisting of Au fishnet structures on a TiO2 spacer/Ag mirror. The fishnet structures excite localized surface plasmon and generate hot electrons from the absorbed photons, while the TiO2 layer induces Fabry–Perot resonance, and the Ag mirror acts as a back reflector. Through optimizing the TiO2 layer thickness, numerical simulation shows that 97% of the incident light is absorbed in the Au layer. The maximum responsivity and external quantum efficiency of the device can approach 5 mA/W and ～1%, respectively, at the wavelength of 700 nm.
Chinese Optics Letters
- Publication Date: May. 10, 2020
- Vol. 18, Issue 5, 052402 (2020)
Wide range bilayer aluminum nanowire grating sensors with robust reflective peaks
Zhicheng Ye, and Jun Zheng
A grating-coupled surface plasmon resonance sensor based on bilayer aluminum nanowire arrays is fabricated by laser interference lithography. The device presents impressive reflective sharp peaks by lateral surface plasmon resonances even for aluminum thicknesses of merely several nanometers. Distinct reflective peaks and dramatic color shifts under different analytes are observed within a wide range of incident angle, metal thickness, and refractive index. The sensitivity of 307 nm per refractive index unit is experimentally obtained. The reflective-peak-type surface plasmon resonance sensors are suitable for practical applications because of easy fabrication, low cost, wide range, and high signal visibility. A grating-coupled surface plasmon resonance sensor based on bilayer aluminum nanowire arrays is fabricated by laser interference lithography. The device presents impressive reflective sharp peaks by lateral surface plasmon resonances even for aluminum thicknesses of merely several nanometers. Distinct reflective peaks and dramatic color shifts under different analytes are observed within a wide range of incident angle, metal thickness, and refractive index. The sensitivity of 307 nm per refractive index unit is experimentally obtained. The reflective-peak-type surface plasmon resonance sensors are suitable for practical applications because of easy fabrication, low cost, wide range, and high signal visibility.
Chinese Optics Letters
- Publication Date: May. 10, 2020
- Vol. 18, Issue 5, 052401 (2020)
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