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Surface Optics and Plasmonics|107 Article(s)
High-performance portable grating-based surface plasmon resonance sensor using a tunable laser at normal incidence
Duc Le, Anni Ranta-Lassila, Teemu Sipola, Mikko Karppinen, Jarno Petäjä, Minna Kehusmaa, Sanna Aikio, Tian-Long Guo, Matthieu Roussey, Jussi Hiltunen, and Alexey Popov
Surface plasmon resonance (SPR) sensors are among the most sensitive sensors. In such devices, a grating is a compelling alternative to a prism for the excitation of a surface plasmon, especially in the development of sensors for point-of-care applications due to their compactness and cost-effectiveness. Here, we demonstrate the use of a tunable laser in a grating-based SPR system for further miniaturization and integration. The tunable laser working at normal incidence replaces spectral and moving components, while also simplifying the optical setup. Normal incidence is conventionally avoided due to the complexity of the control of degenerated SPR modes. We investigate, both computationally and experimentally, the splitting of the SPR modes at small nonzero incidences, which is lacking in previously reported studies. By optimizing the grating configuration, we were able to diminish the SPR mode splitting phenomenon when the excitation was feasible with the normal incidence configuration. The fabricated sensor showed a high sensitivity of 1101.6 nm/RIU. Notably, the figure of merit of the sensor, defined as the ratio between the sensitivity and bandwidth of the SPR dip, was 229.5. The experimental results were consistent with the simulation results. We also demonstrate its capability for detecting low concentrations of glucose and creatinine with the limit of detection of 14.2 and 19.1 mmol/L, respectively. Surface plasmon resonance (SPR) sensors are among the most sensitive sensors. In such devices, a grating is a compelling alternative to a prism for the excitation of a surface plasmon, especially in the development of sensors for point-of-care applications due to their compactness and cost-effectiveness. Here, we demonstrate the use of a tunable laser in a grating-based SPR system for further miniaturization and integration. The tunable laser working at normal incidence replaces spectral and moving components, while also simplifying the optical setup. Normal incidence is conventionally avoided due to the complexity of the control of degenerated SPR modes. We investigate, both computationally and experimentally, the splitting of the SPR modes at small nonzero incidences, which is lacking in previously reported studies. By optimizing the grating configuration, we were able to diminish the SPR mode splitting phenomenon when the excitation was feasible with the normal incidence configuration. The fabricated sensor showed a high sensitivity of 1101.6 nm/RIU. Notably, the figure of merit of the sensor, defined as the ratio between the sensitivity and bandwidth of the SPR dip, was 229.5. The experimental results were consistent with the simulation results. We also demonstrate its capability for detecting low concentrations of glucose and creatinine with the limit of detection of 14.2 and 19.1 mmol/L, respectively.
Photonics Research
- Publication Date: May. 01, 2024
- Vol. 12, Issue 5, 947 (2024)
Terahertz sensing with a 3D meta-absorbing chip based on two-photon polymerization printing|Editors' Pick
Xueer Chen, Longfang Ye, and Daquan Yu
The narrowband meta-absorbers exhibit significantly enhanced electromagnetic confinement capabilities, showcasing broad application prospects in sensing fields. They can be applied for biomarker detection, chemical composition analysis, and monitoring of specific gas in the environment. In this work, we propose a 3D meta-absorber with an out-of-plane plasma mechanism based on a two-photon printing system. Compared to the conventional fabrication of a metal-insulator-metal 2D meta-absorber, the 3D absorber is composed of a metal layer and a resin layer from top to bottom; its manufacturing process is simpler, only including two-photon printing and magnetron sputtering deposition. A noticeable absorbing resonance appears at 0.3142 THz with perfect absorbance with a high Q-factor of 104.67. The theoretical sensitivity to the refractive index of the sensor reaches up to 172.5 GHz/RIU, with a figure of merit (FOM) of 19.56. In the experiments, it was validated as a meta-absorber with high sensitivity for doxycycline (DCH). As the DCH concentration increases from 0 to 4 mg/mL, the absorption intensity decreases around 49%, while the resonant frequency shift is around 70 GHz. It reflects the real-time residual content of DCH, and is potentially applied in trace antibiotic detection. The results showcase a perfect narrowband absorption capability with strong electromagnetic confinement in the terahertz spectrum, along with high-Q sensing characteristics of DCH. Compared to 2D metamaterials, the diversity of 3D metamaterial significantly expands, and introduces additional effects to provide greater flexibility in manipulating electromagnetic waves. The 3D device offers opportunities for the application of terahertz biochemical sensing. The narrowband meta-absorbers exhibit significantly enhanced electromagnetic confinement capabilities, showcasing broad application prospects in sensing fields. They can be applied for biomarker detection, chemical composition analysis, and monitoring of specific gas in the environment. In this work, we propose a 3D meta-absorber with an out-of-plane plasma mechanism based on a two-photon printing system. Compared to the conventional fabrication of a metal-insulator-metal 2D meta-absorber, the 3D absorber is composed of a metal layer and a resin layer from top to bottom; its manufacturing process is simpler, only including two-photon printing and magnetron sputtering deposition. A noticeable absorbing resonance appears at 0.3142 THz with perfect absorbance with a high Q-factor of 104.67. The theoretical sensitivity to the refractive index of the sensor reaches up to 172.5 GHz/RIU, with a figure of merit (FOM) of 19.56. In the experiments, it was validated as a meta-absorber with high sensitivity for doxycycline (DCH). As the DCH concentration increases from 0 to 4 mg/mL, the absorption intensity decreases around 49%, while the resonant frequency shift is around 70 GHz. It reflects the real-time residual content of DCH, and is potentially applied in trace antibiotic detection. The results showcase a perfect narrowband absorption capability with strong electromagnetic confinement in the terahertz spectrum, along with high-Q sensing characteristics of DCH. Compared to 2D metamaterials, the diversity of 3D metamaterial significantly expands, and introduces additional effects to provide greater flexibility in manipulating electromagnetic waves. The 3D device offers opportunities for the application of terahertz biochemical sensing.
Photonics Research
- Publication Date: Apr. 12, 2024
- Vol. 12, Issue 5, 895 (2024)
Simplistic framework of single-pixel-programmable metasurfaces integrated with a capsuled LED array
Yuxi Li, Jiafu Wang, Sai Sui, Ruichao Zhu, Yajuan Han, Hongya Chen, Xinmin Fu, Shaojie Wang, Cunqian Feng, and Shaobo Qu
Coding metasurfaces can manipulate electromagnetic wave in real time with high degree of freedom, the fascinating properties of which enrich the metasurface design with a wide range of application prospects. However, most of the coding metasurfaces are designed based on external excitation framework with the wired electrical or wireless light control devices, thus inevitably causing the interference with electromagnetic wave transmission and increasing the complexity of the metasurface design. In this work, a simplistic framework of single-pixel-programmable metasurfaces integrated with a capsuled LED array is proposed to dynamically control electromagnetic wave. The framework fully embeds the photoresistor in the meta-atom, controlling the LED array to directly illuminate the photoresistor to modulate the phase response. With this manner, the complex biasing network is transformed to the universal LED array, which means the physical control framework can be transformed to a software framework, and thus the functions of the metasurface can be freely manipulated by encoding the capsuled LED array avoiding mutual coupling of adjacent meta-atoms in real time. All the results verify that the far-field scattering pattern can be customized with this single-pixel-programmable metasurface. Encouragingly, this work provides a universal framework for coding metasurface design, which lays the foundation for metasurface intelligent perception and adaptive modulation. Coding metasurfaces can manipulate electromagnetic wave in real time with high degree of freedom, the fascinating properties of which enrich the metasurface design with a wide range of application prospects. However, most of the coding metasurfaces are designed based on external excitation framework with the wired electrical or wireless light control devices, thus inevitably causing the interference with electromagnetic wave transmission and increasing the complexity of the metasurface design. In this work, a simplistic framework of single-pixel-programmable metasurfaces integrated with a capsuled LED array is proposed to dynamically control electromagnetic wave. The framework fully embeds the photoresistor in the meta-atom, controlling the LED array to directly illuminate the photoresistor to modulate the phase response. With this manner, the complex biasing network is transformed to the universal LED array, which means the physical control framework can be transformed to a software framework, and thus the functions of the metasurface can be freely manipulated by encoding the capsuled LED array avoiding mutual coupling of adjacent meta-atoms in real time. All the results verify that the far-field scattering pattern can be customized with this single-pixel-programmable metasurface. Encouragingly, this work provides a universal framework for coding metasurface design, which lays the foundation for metasurface intelligent perception and adaptive modulation.
Photonics Research
- Publication Date: Apr. 12, 2024
- Vol. 12, Issue 5, 884 (2024)
On-chip terahertz orbital angular momentum demultiplexer|Editors' Pick
Xiaohan Jiang, Wanying Liu, Quan Xu, Yuanhao Lang, Yikai Fu, Fan Huang, Haitao Dai, Yanfeng Li, Xueqian Zhang, Jianqiang Gu, Jiaguang Han, and Weili Zhang
The terahertz regime is widely recognized as a fundamental domain with significant potential to address the demands of next-generation wireless communications. In parallel, mode division multiplexing based on orbital angular momentum (OAM) shows promise in enhancing bandwidth utilization, thereby expanding the overall communication channel capacity. In this study, we present both theoretical and experimental demonstrations of an on-chip terahertz OAM demultiplexer. This device effectively couples and steers seven incident terahertz vortex beams into distinct high-quality focusing surface plasmonic beams, and the focusing directions can be arbitrarily designated. The proposed design strategy integrates space-to-chip mode conversion, OAM recognition, and on-chip routing in a compact space with subwavelength thickness, exhibiting versatility and superior performance. The terahertz regime is widely recognized as a fundamental domain with significant potential to address the demands of next-generation wireless communications. In parallel, mode division multiplexing based on orbital angular momentum (OAM) shows promise in enhancing bandwidth utilization, thereby expanding the overall communication channel capacity. In this study, we present both theoretical and experimental demonstrations of an on-chip terahertz OAM demultiplexer. This device effectively couples and steers seven incident terahertz vortex beams into distinct high-quality focusing surface plasmonic beams, and the focusing directions can be arbitrarily designated. The proposed design strategy integrates space-to-chip mode conversion, OAM recognition, and on-chip routing in a compact space with subwavelength thickness, exhibiting versatility and superior performance.
Photonics Research
- Publication Date: May. 01, 2024
- Vol. 12, Issue 5, 1044 (2024)
Lead-free perovskite Cs2AgBiBr6 photodetector detecting NIR light driven by titanium nitride plasmonic hot holes|Editors' Pick
Zijian Liu, Yuying Xi, Wenbo Zeng, Ting Ji, Wenyan Wang, Sitong Guo, Linlin Shi, Rong Wen, Yanxia Cui, and Guohui Li
Lead-free perovskite Cs2AgBiBr6 manifests great potential in developing high-performance, environmentally friendly, solution-processable photodetectors (PDs). However, due to the relatively large energy bandgap, the spectrum responses of Cs2AgBiBr6 PDs are limited to the ultraviolet and visible region with wavelengths shorter than 560 nm. In this work, a broadband Cs2AgBiBr6 PD covering the ultraviolet, visible, and near infrared (NIR) range is demonstrated by incorporating titanium nitride (TiN) nanoparticles that are prepared with the assistance of self-assembled polystyrene sphere array. In addition, an atomically thick Al2O3 layer is introduced at the interface between the Cs2AgBiBr6 film and TiN nanoparticles to alleviate the dark current deterioration caused by nanoparticle incorporation. As a result, beyond the spectrum range where Cs2AgBiBr6 absorbs light, the external quantum efficiency (EQE) of the TiN nanoparticle incorporated Cs2AgBiBr6 PD is enhanced significantly compared with that of the control, displaying enhancement factors as high as 2000 over a broadband NIR wavelength range. The demonstrated enhancement in EQE arises from the photocurrent contribution of plasmonic hot holes injected from TiN nanoparticles into Cs2AgBiBr6. This work promotes the development of broadband solution-processable perovskite PDs, providing a promising strategy for realizing photodetection in the NIR region. Lead-free perovskite Cs2AgBiBr6 manifests great potential in developing high-performance, environmentally friendly, solution-processable photodetectors (PDs). However, due to the relatively large energy bandgap, the spectrum responses of Cs2AgBiBr6 PDs are limited to the ultraviolet and visible region with wavelengths shorter than 560 nm. In this work, a broadband Cs2AgBiBr6 PD covering the ultraviolet, visible, and near infrared (NIR) range is demonstrated by incorporating titanium nitride (TiN) nanoparticles that are prepared with the assistance of self-assembled polystyrene sphere array. In addition, an atomically thick Al2O3 layer is introduced at the interface between the Cs2AgBiBr6 film and TiN nanoparticles to alleviate the dark current deterioration caused by nanoparticle incorporation. As a result, beyond the spectrum range where Cs2AgBiBr6 absorbs light, the external quantum efficiency (EQE) of the TiN nanoparticle incorporated Cs2AgBiBr6 PD is enhanced significantly compared with that of the control, displaying enhancement factors as high as 2000 over a broadband NIR wavelength range. The demonstrated enhancement in EQE arises from the photocurrent contribution of plasmonic hot holes injected from TiN nanoparticles into Cs2AgBiBr6. This work promotes the development of broadband solution-processable perovskite PDs, providing a promising strategy for realizing photodetection in the NIR region.
Photonics Research
- Publication Date: Mar. 01, 2024
- Vol. 12, Issue 3, 522 (2024)
Full-Stokes metasurface polarimetry requiring only a single measurement
Chenglong Zheng, Hui Li, Jingyu Liu, Mengguang Wang, Huaping Zang, Yan Zhang, and Jianquan Yao
Polarization is crucial in various fields such as imaging, sensing, and substance detection. A compact, fast, and accurate polarization detection device is vital for these applications. Herein, we demonstrate a multifocus metalens for terahertz polarization detection that requires only a single measurement to obtain complete polarization parameters and reconstruct the polarization state of the incident field. The individual subarrays of this metalens convert each of the six polarized components into the same polarization, which in turn links the Stokes parameters to these six foci. The incident linear polarizations and elliptical polarizations are characterized by Stokes parameters and polarization ellipses. Simulations and experimental results show that the scheme can accurately detect the incident polarization with a single measurement. The proposed metasurface polarimetry may find applications in the fields of real-time terahertz detection and integrated optics. Polarization is crucial in various fields such as imaging, sensing, and substance detection. A compact, fast, and accurate polarization detection device is vital for these applications. Herein, we demonstrate a multifocus metalens for terahertz polarization detection that requires only a single measurement to obtain complete polarization parameters and reconstruct the polarization state of the incident field. The individual subarrays of this metalens convert each of the six polarized components into the same polarization, which in turn links the Stokes parameters to these six foci. The incident linear polarizations and elliptical polarizations are characterized by Stokes parameters and polarization ellipses. Simulations and experimental results show that the scheme can accurately detect the incident polarization with a single measurement. The proposed metasurface polarimetry may find applications in the fields of real-time terahertz detection and integrated optics.
Photonics Research
- Publication Date: Mar. 01, 2024
- Vol. 12, Issue 3, 514 (2024)
Flexible tuning of multifocal holographic imaging based on electronically controlled metasurfaces
Bowen Zeng, Chenxia Li, Bo Fang, Zhi Hong, and Xufeng Jing
Programmable hyper-coded holography has the advantage of being programmable as well as being flexibly modifiable. Digitally coded metamaterials with excellent electromagnetic modulation capability and the ability to control the phase to modulate the spatial radiation field through external excitation in the form of switching can be used to realize low-cost digital arrays. We design a 1-bit encoded programmable metasurface, which is electrically connected to control the PIN diode in the switching state and to switch the condition of each metasurface cell between “0” and “1.” Using the designed programmable metasurface, we can randomly encode the cell structure to realize single-focus focusing, multi-focusing, and simple holographic letter imaging. Based on the nonlinear holographic model, we employ the Gerchberg-Saxton improvement algorithm to modulate the energy distribution at the focus by adjusting the phase distribution. Importantly, we introduce the Fourier convolution principle to regulate the holographic imaging focus flexibly. Programmable hyper-coded holography has the advantage of being programmable as well as being flexibly modifiable. Digitally coded metamaterials with excellent electromagnetic modulation capability and the ability to control the phase to modulate the spatial radiation field through external excitation in the form of switching can be used to realize low-cost digital arrays. We design a 1-bit encoded programmable metasurface, which is electrically connected to control the PIN diode in the switching state and to switch the condition of each metasurface cell between “0” and “1.” Using the designed programmable metasurface, we can randomly encode the cell structure to realize single-focus focusing, multi-focusing, and simple holographic letter imaging. Based on the nonlinear holographic model, we employ the Gerchberg-Saxton improvement algorithm to modulate the energy distribution at the focus by adjusting the phase distribution. Importantly, we introduce the Fourier convolution principle to regulate the holographic imaging focus flexibly.
Photonics Research
- Publication Date: Dec. 21, 2023
- Vol. 12, Issue 1, 61 (2024)
All-plasmonic optical leaky-wave antenna with a low sidelobe level
Guang Zhu Zhou, Bao-Jie Chen, Geng-Bo Wu, Shi-Wei Qu, and Chi Hou Chan
Optical antennas have received considerable attention in recent years due to their unique ability to convert localized energy to freely propagating radiation and vice versa. Sidelobe level (SLL) is one of the most crucial parameters in antenna design. A low SLL is beneficial to minimize the antenna interference with other optical components. Here a plasmonic optical leaky-wave antenna with low SLL is reported. Shifting spatial frequency by periodically modulating the electric-field amplitude in a plasmonic gap waveguide enables a free-space coupled wave out of the antenna. At the same time, precise control of the aperture fields by the modulation depth allows for reducing SLL. Simulation results indicate that the proposed design can achieve a high directivity of 15.8 dB and a low SLL of -20 dB at the wavelength of 1550 nm. A low SLL below -15 dB is experimentally demonstrated within the wavelength range from 1527 to 1570 nm. In addition, the low-SLL property is further verified by comparing it with a uniformly modulated antenna. By modulating the guided waves in the plasmonic gap waveguide in different forms, the aperture fields can be flexibly arranged to achieve arbitrary wavefront shaping. It bridges the gap between guided and free-space waves and empowers plasmonic integrated devices to control free-space light, thus enabling various free-space functions. Optical antennas have received considerable attention in recent years due to their unique ability to convert localized energy to freely propagating radiation and vice versa. Sidelobe level (SLL) is one of the most crucial parameters in antenna design. A low SLL is beneficial to minimize the antenna interference with other optical components. Here a plasmonic optical leaky-wave antenna with low SLL is reported. Shifting spatial frequency by periodically modulating the electric-field amplitude in a plasmonic gap waveguide enables a free-space coupled wave out of the antenna. At the same time, precise control of the aperture fields by the modulation depth allows for reducing SLL. Simulation results indicate that the proposed design can achieve a high directivity of 15.8 dB and a low SLL of -20 dB at the wavelength of 1550 nm. A low SLL below -15 dB is experimentally demonstrated within the wavelength range from 1527 to 1570 nm. In addition, the low-SLL property is further verified by comparing it with a uniformly modulated antenna. By modulating the guided waves in the plasmonic gap waveguide in different forms, the aperture fields can be flexibly arranged to achieve arbitrary wavefront shaping. It bridges the gap between guided and free-space waves and empowers plasmonic integrated devices to control free-space light, thus enabling various free-space functions.
Photonics Research
- Publication Date: Aug. 11, 2023
- Vol. 11, Issue 9, 1500 (2023)
Anomalous plasmon coupling and Fano resonance under structured light
Da-Jie Yang, Song-Jin Im, Hai-Wen Huang, Chol-Song Ri, Kum-Dong Kim, Kil-Song Song, Ji-Cai Liu, and Qu-Quan Wang
Structured light carrying orbital angular momentum (OAM) opens up a new physical dimension for studying light–matter interactions. Despite this, the complex fields created by OAM beams still remain largely unexplored in terms of their effects on surface plasmons. This paper presents a revelation of anomalous plasmon excitations in single particles and plasmon couplings of neighboring nanorods under OAM beams, which are forbidden using non-OAM sources. The plasmon excitation of single nanoparticles is determined both by photon spin angular momentum (SAM) and OAM and influenced by the locations of the nanoparticles. Specifically, when SAM and OAM are equal in magnitude and opposite in direction, a pure plasmon excitation along light propagation direction is achieved. Two plasmon dipoles show end-to-end antibonding coupling and side-by-side bounding coupling, which are the opposite of the typical couplings. Furthermore, we observe Fano resonance with a nanorod dimer: one aligned along light propagation direction acting as the bright mode and the other aligned along the global polarization direction of light acting as the dark mode, which is the opposite of the usual plasmonic Fano resonance. By taking advantage of the unique property of the OAM source, this investigation presents a novel way to control and study surface plasmons, and the research of plasmon behavior with OAM would open new avenues for controlling electromagnetic waves and enriching the spectroscopies with more degrees of freedom. Structured light carrying orbital angular momentum (OAM) opens up a new physical dimension for studying light–matter interactions. Despite this, the complex fields created by OAM beams still remain largely unexplored in terms of their effects on surface plasmons. This paper presents a revelation of anomalous plasmon excitations in single particles and plasmon couplings of neighboring nanorods under OAM beams, which are forbidden using non-OAM sources. The plasmon excitation of single nanoparticles is determined both by photon spin angular momentum (SAM) and OAM and influenced by the locations of the nanoparticles. Specifically, when SAM and OAM are equal in magnitude and opposite in direction, a pure plasmon excitation along light propagation direction is achieved. Two plasmon dipoles show end-to-end antibonding coupling and side-by-side bounding coupling, which are the opposite of the typical couplings. Furthermore, we observe Fano resonance with a nanorod dimer: one aligned along light propagation direction acting as the bright mode and the other aligned along the global polarization direction of light acting as the dark mode, which is the opposite of the usual plasmonic Fano resonance. By taking advantage of the unique property of the OAM source, this investigation presents a novel way to control and study surface plasmons, and the research of plasmon behavior with OAM would open new avenues for controlling electromagnetic waves and enriching the spectroscopies with more degrees of freedom.
Photonics Research
- Publication Date: Aug. 01, 2023
- Vol. 11, Issue 8, 1423 (2023)
BICs-enhanced active terahertz wavefront modulator enabled by laser-cut graphene ribbons|On the Cover
Jianzhou Huang, Bin Hu, Guocui Wang, Zongyuan Wang, Jinlong Li, Juan Liu, and Yan Zhang
Graphene-based terahertz (THz) metasurfaces combined with metallic antennas have the advantages of ultra-small thickness, electrical tunability, and fast tuning speed. However, their tuning ability is limited by non-independently tunable pixels and low modulation depth due to the ultra-small thickness of graphene. Here, we demonstrate a reconfigurable THz phase modulator with 5×5 independently tunable units enabled by switching the voltages applied on 10 graphene ribbons prepared by laser cutting. In addition, by introducing quasi-bound states in the continuum resonance through a designed double C-shaped antenna, the efficiency of the device is enhanced by 2.7–3.6 times under different graphene chemical potentials. Experimental results demonstrate that a focus can be formed, and the focal length is changed from 14.3 mm to 22.6 mm. This work provides potential for compact THz spatial light modulators that may be applied in THz communication, detection, and imaging. Graphene-based terahertz (THz) metasurfaces combined with metallic antennas have the advantages of ultra-small thickness, electrical tunability, and fast tuning speed. However, their tuning ability is limited by non-independently tunable pixels and low modulation depth due to the ultra-small thickness of graphene. Here, we demonstrate a reconfigurable THz phase modulator with 5×5 independently tunable units enabled by switching the voltages applied on 10 graphene ribbons prepared by laser cutting. In addition, by introducing quasi-bound states in the continuum resonance through a designed double C-shaped antenna, the efficiency of the device is enhanced by 2.7–3.6 times under different graphene chemical potentials. Experimental results demonstrate that a focus can be formed, and the focal length is changed from 14.3 mm to 22.6 mm. This work provides potential for compact THz spatial light modulators that may be applied in THz communication, detection, and imaging.
Photonics Research
- Publication Date: Jun. 19, 2023
- Vol. 11, Issue 7, 1185 (2023)
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