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Surface Optics and Plasmonics|89 Article(s)
Complementary transmissive ultra-thin meta-deflectors for broadband polarization-independent refractions in the microwave region
Yueyi Yuan, Kuang Zhang, Xumin Ding, Badreddine Ratni, Shah Nawaz Burokur, and Qun Wu
Polarization manipulation is a significant issue for artificial modulation of the electromagnetic (EM) wave, but general mechanisms all suffer the restriction of inherent symmetric properties between opposite handedness. Herein, a strategy to independently and arbitrarily manipulate the EM wave with orthogonal circular polarizations based on a metasurface is proposed, which effectually breaks through traditional symmetrical characteristics between orthogonal handedness. By synthesizing the propagation phase and geometric phase, the appropriate Jones matrix is calculated to obtain independent wavefront manipulation of EM waves with opposite circular polarizations. Two transmissive ultra-thin meta-deflectors are proposed to demonstrate the asymmetrical refraction of transmitted circularly polarized waves in the microwave region. Simulated transmitted phase front and measured far-field intensity distributions are in excellent agreement, indicating that the transmitted wave with different polarizations can be refracted into arbitrary and independent directions within a wide frequency band (relative bandwidth of 25%). The results presented in this paper provide more freedom for the manipulation of EM waves, and motivate the realizations of various polarization-independent properties for all frequency spectra. Polarization manipulation is a significant issue for artificial modulation of the electromagnetic (EM) wave, but general mechanisms all suffer the restriction of inherent symmetric properties between opposite handedness. Herein, a strategy to independently and arbitrarily manipulate the EM wave with orthogonal circular polarizations based on a metasurface is proposed, which effectually breaks through traditional symmetrical characteristics between orthogonal handedness. By synthesizing the propagation phase and geometric phase, the appropriate Jones matrix is calculated to obtain independent wavefront manipulation of EM waves with opposite circular polarizations. Two transmissive ultra-thin meta-deflectors are proposed to demonstrate the asymmetrical refraction of transmitted circularly polarized waves in the microwave region. Simulated transmitted phase front and measured far-field intensity distributions are in excellent agreement, indicating that the transmitted wave with different polarizations can be refracted into arbitrary and independent directions within a wide frequency band (relative bandwidth of 25%). The results presented in this paper provide more freedom for the manipulation of EM waves, and motivate the realizations of various polarization-independent properties for all frequency spectra.
Photonics Research
- Publication Date: Jan. 01, 2019
- Vol. 7, Issue 1, 01000080 (2019)
Plasmonic metasurface Luneburg lens
C. E. Garcia-Ortiz, R. Cortes, J. E. Gómez-Correa, E. Pisano, J. Fiutowski, D. A. Garcia-Ortiz, V. Ruiz-Cortes, H.-G. Rubahn, and V. Coello
We present a new design of a plasmonic Luneburg lens made from a gradient-index metasurface that was constructed with an array of nanometer-sized holes in a dielectric thin film. The fabricated structure consists of a planar lens with a diameter of 8.7 μm composed of a rectangular array of holes with a periodicity of 300 nm. The experimental characterization includes leakage-radiation microscopy imaging in the direction and frequency space. The former allows for characterization of the point spread function and phase distribution, whereas the latter grants access to qualitative measurements of the effective mode indices inside the plasmonic lens. The experimental results presented here are in good agreement with the expected average performance predicted by the numerical calculations. Nevertheless, the robustness of the characterization techniques presented here is also exploited to determine deviations from the design parameters. We present a new design of a plasmonic Luneburg lens made from a gradient-index metasurface that was constructed with an array of nanometer-sized holes in a dielectric thin film. The fabricated structure consists of a planar lens with a diameter of 8.7 μm composed of a rectangular array of holes with a periodicity of 300 nm. The experimental characterization includes leakage-radiation microscopy imaging in the direction and frequency space. The former allows for characterization of the point spread function and phase distribution, whereas the latter grants access to qualitative measurements of the effective mode indices inside the plasmonic lens. The experimental results presented here are in good agreement with the expected average performance predicted by the numerical calculations. Nevertheless, the robustness of the characterization techniques presented here is also exploited to determine deviations from the design parameters.
Photonics Research
- Publication Date: Sep. 04, 2019
- Vol. 7, Issue 10, 10001112 (2019)
Microfluidic integrated metamaterials for active terahertz photonics|Editors' Pick
Zhang Zhang, Ju Gao, Maosheng Yang, Xin Yan, Yuying Lu, Liang Wu, Jining Li, Dequan Wei, Longhai Liu, Jianhua Xie, Lanju Liang, and Jianquan Yao
A depletion layer played by aqueous organic liquids flowing in a platform of microfluidic integrated metamaterials is experimentally used to actively modulate terahertz (THz) waves. The polar configuration of water molecules in a depletion layer gives rise to a damping of THz waves. The parallel coupling of the damping effect induced by a depletion layer with the resonant response by metamaterials leads to an excellent modulation depth approaching 90% in intensity and a great difference over 210° in phase shift. Also, a tunability of slow-light effect is displayed. Joint time-frequency analysis performed by the continuous wavelet transforms reveals the consumed energy with varying water content, indicating a smaller moment of inertia related to a shortened relaxation time of the depletion layer. This work, as part of THz aqueous photonics, diametrically highlights the availability of water in THz devices, paving an alternative way of studying THz wave–liquid interactions and developing active THz photonics. A depletion layer played by aqueous organic liquids flowing in a platform of microfluidic integrated metamaterials is experimentally used to actively modulate terahertz (THz) waves. The polar configuration of water molecules in a depletion layer gives rise to a damping of THz waves. The parallel coupling of the damping effect induced by a depletion layer with the resonant response by metamaterials leads to an excellent modulation depth approaching 90% in intensity and a great difference over 210° in phase shift. Also, a tunability of slow-light effect is displayed. Joint time-frequency analysis performed by the continuous wavelet transforms reveals the consumed energy with varying water content, indicating a smaller moment of inertia related to a shortened relaxation time of the depletion layer. This work, as part of THz aqueous photonics, diametrically highlights the availability of water in THz devices, paving an alternative way of studying THz wave–liquid interactions and developing active THz photonics.
Photonics Research
- Publication Date: Nov. 15, 2019
- Vol. 7, Issue 12, 12001400 (2019)
Azimuthal vector beam exciting silver triangular nanoprisms for increasing the performance of surface-enhanced Raman spectroscopy
Lu Zhang, Wending Zhang, Fanfan Lu, Zhiqiang Yang, Tianyang Xue, Min Liu, Chao Meng, Peng Li, Dong Mao, Ting Mei, and Jianlin Zhao
Surface-enhanced Raman spectroscopy (SERS) with high-sensitivity performance is a very necessary detection technology. Here, we present a method for increasing the performance of SERS based on silver triangular nanoprism arrays (ATNAs) vertically excited via a focused azimuthal vector beam (AVB). The ATNA substrates with different structural parameters are prepared based on the traditional self-assembled and modified film lift-off technique. Based on a theoretical model established adopting the structural parameters of the ATNA substrates, theoretical simulation results show that AVB excitation can achieve greater electric-field enhancement than linearly polarized beam (LPB) excitation. Experimental result indicates that SERS sensitivity obtained via AVB excitation is 10 13 M (1 M = 1 mol/L) using rhodamine 6G (R6G) as the target analyte, which is 2 orders of magnitude lower than that of LPB excitation (10 11 M). Meanwhile, the uniformity and reproducibility of the ATNA substrates are examined using Raman mapping and batch-to-batch measurement, respectively, and the Raman enhancement factor is calculated to be ～3.3×107. This method of vector light field excitation may be used to improve the SERS performance of the substrates in fields of ultra-sensitive Raman detection. Surface-enhanced Raman spectroscopy (SERS) with high-sensitivity performance is a very necessary detection technology. Here, we present a method for increasing the performance of SERS based on silver triangular nanoprism arrays (ATNAs) vertically excited via a focused azimuthal vector beam (AVB). The ATNA substrates with different structural parameters are prepared based on the traditional self-assembled and modified film lift-off technique. Based on a theoretical model established adopting the structural parameters of the ATNA substrates, theoretical simulation results show that AVB excitation can achieve greater electric-field enhancement than linearly polarized beam (LPB) excitation. Experimental result indicates that SERS sensitivity obtained via AVB excitation is 10 13 M (1 M = 1 mol/L) using rhodamine 6G (R6G) as the target analyte, which is 2 orders of magnitude lower than that of LPB excitation (10 11 M). Meanwhile, the uniformity and reproducibility of the ATNA substrates are examined using Raman mapping and batch-to-batch measurement, respectively, and the Raman enhancement factor is calculated to be ～3.3×107. This method of vector light field excitation may be used to improve the SERS performance of the substrates in fields of ultra-sensitive Raman detection.
Photonics Research
- Publication Date: Nov. 27, 2019
- Vol. 7, Issue 12, 12001447 (2019)
Routing emission with a multi-channel nonreciprocal waveguide
Hao Hu, Liangliang Liu, Xiao Hu, Dongjue Liu, and Dongliang Gao
In this work, we present a multi-channel nonreciprocal waveguide, which is composed of a gyrotropic-bounded dielectric on the bottom and a plasmonic material on the top. The Lorentz reciprocity in the time-invariant system is broken when applying an external static magnetic field on the gyrotropic material. The nonreciprocal emission from the dipole source located in the center of the waveguide is observed in extended waveband channels. The proposed heterostructure serves as a photonic dichroism once the dielectric is replaced by a nonlinear material. The associated second harmonic generated in the nonlinear process can be separated from the fundamental signal under proper magnetic field intensity. Our findings may provide significant guidance for designing nonreciprocal photonic devices with superiorities of a tunable waveband, multiple channels, and small footprint. In this work, we present a multi-channel nonreciprocal waveguide, which is composed of a gyrotropic-bounded dielectric on the bottom and a plasmonic material on the top. The Lorentz reciprocity in the time-invariant system is broken when applying an external static magnetic field on the gyrotropic material. The nonreciprocal emission from the dipole source located in the center of the waveguide is observed in extended waveband channels. The proposed heterostructure serves as a photonic dichroism once the dielectric is replaced by a nonlinear material. The associated second harmonic generated in the nonlinear process can be separated from the fundamental signal under proper magnetic field intensity. Our findings may provide significant guidance for designing nonreciprocal photonic devices with superiorities of a tunable waveband, multiple channels, and small footprint.
Photonics Research
- Publication Date: May. 15, 2019
- Vol. 7, Issue 6, 06000642 (2019)
Alloyed Au-Ag nanorods with desired plasmonic properties and stability in harsh environments
Yuan Ni, Caixia Kan, Longbing He, Xingzhong Zhu, Mingming Jiang, and Daning Shi
Bio-chemical molecular detection in the nanoscale, based on alloyed nanorods (NRs) with tunable surface plasmon resonance (SPR) properties and high chemical stability, has attracted particular interest. In this work, alloyed Au-Ag NRs with tunable aspect ratios were achieved by annealing Au nanobipyramid-directed Au@Ag core-shell NRs. The core-shell NRs were encapsulated within mesoporous silica outer shells to avoid fusion or aggregation. The structural stability of fully alloyed Au-Ag NRs, including chemical and thermal stability, is remarkably improved compared with that of Au@Ag core-shell NRs. The alloyed NRs would maintain the rod-like structure after being incubated in etchant solution, while Au@Ag core-shell NRs would decay into nanobipyramids. Additionally, fully alloyed NRs present stable morphology under annealing at high temperatures of up to 600°C in air. Benefiting from excellent structural and chemical stabilities, the surface-enhanced Raman scattering effect based on alloyed NRs is stable in harsh environments. Taking advantage of tunable SPR properties (600–1800 nm) and excellent stability, the obtained nanostructures can serve as drug carriers. The perfect photo-thermal effect induced by the particular SPR of alloyed NRs can improve the release efficiency of drugs. Bio-chemical molecular detection in the nanoscale, based on alloyed nanorods (NRs) with tunable surface plasmon resonance (SPR) properties and high chemical stability, has attracted particular interest. In this work, alloyed Au-Ag NRs with tunable aspect ratios were achieved by annealing Au nanobipyramid-directed Au@Ag core-shell NRs. The core-shell NRs were encapsulated within mesoporous silica outer shells to avoid fusion or aggregation. The structural stability of fully alloyed Au-Ag NRs, including chemical and thermal stability, is remarkably improved compared with that of Au@Ag core-shell NRs. The alloyed NRs would maintain the rod-like structure after being incubated in etchant solution, while Au@Ag core-shell NRs would decay into nanobipyramids. Additionally, fully alloyed NRs present stable morphology under annealing at high temperatures of up to 600°C in air. Benefiting from excellent structural and chemical stabilities, the surface-enhanced Raman scattering effect based on alloyed NRs is stable in harsh environments. Taking advantage of tunable SPR properties (600–1800 nm) and excellent stability, the obtained nanostructures can serve as drug carriers. The perfect photo-thermal effect induced by the particular SPR of alloyed NRs can improve the release efficiency of drugs.
Photonics Research
- Publication Date: Apr. 29, 2019
- Vol. 7, Issue 5, 05000558 (2019)
Plasmonic tip internally excited via an azimuthal vector beam for surface enhanced Raman spectroscopy
Min Liu, Wending Zhang, Fanfan Lu, Tianyang Xue, Xin Li, Lu Zhang, Dong Mao, Ligang Huang, Feng Gao, Ting Mei, and Jianlin Zhao
The synergy of a plasmonic tip and fiber-based structure light field excitation can provide a powerful tool for Raman examination. Here, we present a method of Raman spectrum enhancement with an Ag-nanoparticles (Ag-NPs)-coated fiber probe internally excited via an azimuthal vector beam (AVB), which is directly generated in a few-mode fiber by using an acoustically induced fiber grating. Theoretical analysis shows that gap mode can be effectively generated on the surface of the Ag-NPs-coated fiber probe excited via an AVB. The experimental result shows that the intensity of Raman signal obtained with analyte molecules of malachite green by exciting the Ag-NPs-coated fiber probe via an AVB is approximately eight times as strong as that via the linear polarization beam (LPB), and the activity of the AVB-excited fiber probe can reach 10 11 mol/L, which cannot be achieved by LPB excitation. Moreover, the time stability and reliability are also examined, respectively. The synergy of a plasmonic tip and fiber-based structure light field excitation can provide a powerful tool for Raman examination. Here, we present a method of Raman spectrum enhancement with an Ag-nanoparticles (Ag-NPs)-coated fiber probe internally excited via an azimuthal vector beam (AVB), which is directly generated in a few-mode fiber by using an acoustically induced fiber grating. Theoretical analysis shows that gap mode can be effectively generated on the surface of the Ag-NPs-coated fiber probe excited via an AVB. The experimental result shows that the intensity of Raman signal obtained with analyte molecules of malachite green by exciting the Ag-NPs-coated fiber probe via an AVB is approximately eight times as strong as that via the linear polarization beam (LPB), and the activity of the AVB-excited fiber probe can reach 10 11 mol/L, which cannot be achieved by LPB excitation. Moreover, the time stability and reliability are also examined, respectively.
Photonics Research
- Publication Date: Apr. 16, 2019
- Vol. 7, Issue 5, 05000526 (2019)
Self-powered lead-free quantum dot plasmonic phototransistor with multi-wavelength response
Yu Yu, Yating Zhang, Lufan Jin, Zhiliang Chen, Yifan Li, Qingyan Li, Mingxuan Cao, Yongli Che, Haitao Dai, Junbo Yang, and Jianquan Yao
Because they possess excellent visible light absorption properties, lead-free colloidal copper-based chalcogenide quantum dots (QDs) have emerged in photoelectronic fields. By means of localized surface plasmonic resonance (LSPR), the absorption properties of QDs can be enhanced. In this paper, we fabricate a lead-free CuInSe2 QD field effect phototransistor (FEpT) by utilizing the LSPR enhancement of Au nanoparticles (NPs). The plasmonic FEpT demonstrates responsivity up to 2.7 μA·W 1 and a specific detectivity of 7×103 Jones at zero bias under illumination by a 532 nm laser, values that are enhanced by approximately 200% more than devices without Au NPs. Particularly, the FEpT exhibits a multi-wavelength response, which is photoresponsive to 405, 532, and 808 nm irradiations, and presents stability and reproducibility in the progress of ON–OFF cycles. Furthermore, the enhancement induced by Au NP LSPR can be interpreted by finite-difference time domain simulations. The low-cost solution-based process and excellent device performance strongly underscore lead-free CuInSe2 QDs as a promising material for self-powered photoelectronic applications, which can be further enhanced by Au NP LSPR. Because they possess excellent visible light absorption properties, lead-free colloidal copper-based chalcogenide quantum dots (QDs) have emerged in photoelectronic fields. By means of localized surface plasmonic resonance (LSPR), the absorption properties of QDs can be enhanced. In this paper, we fabricate a lead-free CuInSe2 QD field effect phototransistor (FEpT) by utilizing the LSPR enhancement of Au nanoparticles (NPs). The plasmonic FEpT demonstrates responsivity up to 2.7 μA·W 1 and a specific detectivity of 7×103 Jones at zero bias under illumination by a 532 nm laser, values that are enhanced by approximately 200% more than devices without Au NPs. Particularly, the FEpT exhibits a multi-wavelength response, which is photoresponsive to 405, 532, and 808 nm irradiations, and presents stability and reproducibility in the progress of ON–OFF cycles. Furthermore, the enhancement induced by Au NP LSPR can be interpreted by finite-difference time domain simulations. The low-cost solution-based process and excellent device performance strongly underscore lead-free CuInSe2 QDs as a promising material for self-powered photoelectronic applications, which can be further enhanced by Au NP LSPR.
Photonics Research
- Publication Date: Jan. 16, 2019
- Vol. 7, Issue 2, 02000149 (2019)
All-dielectric three-element transmissive Huygens’ metasurface performing anomalous refraction
Chang Liu, Lei Chen, Tiesheng Wu, Yumin Liu, Jing Li, Yu Wang, Zhongyuan Yu, Han Ye, and Li Yu
Metasurfaces have pioneered a new avenue for advanced wave-front engineering. Among the various types of metasurfaces, Huygens’ metasurfaces are thought to be a novel paradigm for flat optical devices. Enabled by spectrally overlapped electric resonance and magnetic resonance, Huygens’ metasurfaces are imparted with high transmission and full phase coverage of 2π, which makes them capable of realizing high-efficiency wave-front control. However, a defect of Huygens’ metasurfaces is that their phase profiles and transmissive responses are often sensitive to the interaction of neighboring Huygens’ elements. Consequently, the original assigned phase distribution can be distorted. In this work, we present our design strategy of transmissive Huygens’ metasurfaces performing anomalous refraction. We illustrate the investigation of Huygens’ elements, realizing the overlapping between an electric dipole and magnetic dipole resonance based on cross-shaped structures. We find that the traditional discrete equidistant-phase design method is not enough to realize a transmissive Huygens’ surface due to the interaction between neighboring Huygens’ elements. Therefore, we introduce an extra optimization process on the element spacing to palliate the phase distortion resulting from the element interaction. Based on this method, we successfully design unequally spaced three-element transmissive metasurfaces exhibiting anomalous refraction effect. The anomalous refractive angle of the designed Huygens’ metasurface is 30°, which exceeds the angles of most present transmissive Huygens’ metasurfaces. A transmissive efficiency of 83.5% is numerically derived at the operating wavelength. The far-field electric distribution shows that about 93% of transmissive light is directed along the 30° refractive direction. The deflection angle can be tuned by adjusting the number of Huygens’ elements in one metasurface unit cell. The design strategies used in this paper can be inspiring for other functional Huygens’ metasurface schemes. Metasurfaces have pioneered a new avenue for advanced wave-front engineering. Among the various types of metasurfaces, Huygens’ metasurfaces are thought to be a novel paradigm for flat optical devices. Enabled by spectrally overlapped electric resonance and magnetic resonance, Huygens’ metasurfaces are imparted with high transmission and full phase coverage of 2π, which makes them capable of realizing high-efficiency wave-front control. However, a defect of Huygens’ metasurfaces is that their phase profiles and transmissive responses are often sensitive to the interaction of neighboring Huygens’ elements. Consequently, the original assigned phase distribution can be distorted. In this work, we present our design strategy of transmissive Huygens’ metasurfaces performing anomalous refraction. We illustrate the investigation of Huygens’ elements, realizing the overlapping between an electric dipole and magnetic dipole resonance based on cross-shaped structures. We find that the traditional discrete equidistant-phase design method is not enough to realize a transmissive Huygens’ surface due to the interaction between neighboring Huygens’ elements. Therefore, we introduce an extra optimization process on the element spacing to palliate the phase distortion resulting from the element interaction. Based on this method, we successfully design unequally spaced three-element transmissive metasurfaces exhibiting anomalous refraction effect. The anomalous refractive angle of the designed Huygens’ metasurface is 30°, which exceeds the angles of most present transmissive Huygens’ metasurfaces. A transmissive efficiency of 83.5% is numerically derived at the operating wavelength. The far-field electric distribution shows that about 93% of transmissive light is directed along the 30° refractive direction. The deflection angle can be tuned by adjusting the number of Huygens’ elements in one metasurface unit cell. The design strategies used in this paper can be inspiring for other functional Huygens’ metasurface schemes.
Photonics Research
- Publication Date: Dec. 01, 2019
- Vol. 7, Issue 12, 12001501 (2019)
Dielectric metalens-based Hartmann–Shack array for a high-efficiency optical multiparameter detection system|Editors' Pick
Yuxi Wang, Zhaokun Wang, Xing Feng, Ming Zhao, Cheng Zeng, Guangqiang He, Zhenyu Yang, Yu Zheng, and Jinsong Xia
The real-time measurement of the polarization and phase information of light is very important and desirable in optics. Metasurfaces can be used to achieve flexible wavefront control and can therefore be used to replace traditional optical elements to produce a highly integrated and extremely compact optical system. Here, we propose an efficient and compact optical multiparameter detection system based on a Hartmann–Shack array with 2×2 subarray metalenses. This system not only enables the efficient and accurate measurement of the spatial polarization profiles of optical beams via the inspection of foci amplitudes, but also measures the phase and phase-gradient profiles by analyzing foci displacements. In this work, details of the design of the elliptical silicon pillars for the metalens are described, and we achieve a high average focusing efficiency of 48% and a high spatial resolution. The performance of the system is validated by the experimental measurement of 22 scalar polarized beams, an azimuthally polarized beam, a radially polarized beam, and a vortex beam. The experimental results are in good agreement with theoretical predictions. The real-time measurement of the polarization and phase information of light is very important and desirable in optics. Metasurfaces can be used to achieve flexible wavefront control and can therefore be used to replace traditional optical elements to produce a highly integrated and extremely compact optical system. Here, we propose an efficient and compact optical multiparameter detection system based on a Hartmann–Shack array with 2×2 subarray metalenses. This system not only enables the efficient and accurate measurement of the spatial polarization profiles of optical beams via the inspection of foci amplitudes, but also measures the phase and phase-gradient profiles by analyzing foci displacements. In this work, details of the design of the elliptical silicon pillars for the metalens are described, and we achieve a high average focusing efficiency of 48% and a high spatial resolution. The performance of the system is validated by the experimental measurement of 22 scalar polarized beams, an azimuthally polarized beam, a radially polarized beam, and a vortex beam. The experimental results are in good agreement with theoretical predictions.
Photonics Research
- Publication Date: Mar. 23, 2020
- Vol. 8, Issue 4, 04000482 (2020)
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