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1. A low-loss molybdenum plasmonic waveguide: perfect single-crystal preparation and subwavelength grating optimization

Author

Cui Tao, Shen Yan, Cheng Ao, Zhan Runze, Zheng Zebo, Tian Bo, Shi Jia, Ke Yanlin, Shao Lei, Chen Huanjun, and Deng Shaozhi

Subjects
plasmonic waveguide, near-infrared, low-loss propagation, molybdenum single-crystal, subwavelength grating, Physics, QC1-999
Abstract

Plasmonic waveguides have attracted tremendous interest due to efficiently confining photons on the subwavelength spatial scale to be beating the propagation diffraction limit. Transition metal molybdenum (Mo) exhibits outstanding properties in light trapping and electromagnetic field confining, making it potentially valuable in 1.55 μm plasmonic waveguide applications. However, the reliable fabrication of high-quality Mo plasmonic waveguides is a significant challenge. A real-space micro-imaging study of the surface plasmon on Mo structures is still absent. In this study, we successfully prepared a single-crystalline Mo microrod waveguide structure and fabricated subwavelength gratings on it. The diffraction gratings were designed, optimized, and etched to excite the surface plasmon polariton behaviour of Mo for the first time. The grating-optimized Mo microrod single-crystal reveals highly efficient waveguide performance around near-infrared spectroscopy, exhibiting a long propagation length of 32 μm and a low transmission loss of 0.067 dB μm−1. The results provide an alternative to advanced materials research and optical device applications of plasmonic waveguide systems.

Published
2023
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2. Tunable Hyperbolic Phonon Polaritons in a Gradiently-Suspended Van Der Waals {\alpha}-MoO3

Author

Zheng, Zebo, Sun, Fengsheng, Huang, Wuchao, Chen, Xuexian, Ke, Yanlin, Zhan, Runze, Chen, Huanjun, and Deng, Shaozhi

Subjects
Physics - Optics
Abstract

Highly confined and low-loss hyperbolic phonon polaritons (HPhPs) sustained in van der Waals crystals exhibit outstanding capabilities of concentrating long-wave electromagnetic fields deep to the subwavelength region. Precise tuning on the HPhP propagation characteristics remains a great challenge for practical applications such as nanophotonic devices and circuits. Here, we show that by taking advantage of the varying air gaps in a van der Waals {\alpha}-MoO3 crystal suspended gradiently, it is able to tune the wavelengths and dampings of the HPhPs propagating inside the {\alpha}-MoO3. The results indicate that the dependences of polariton wavelength on gap distance for HPhPs in lower and upper Reststrahlen bands are opposite to each other. Most interestingly, the tuning range of the polariton wavelengths for HPhPs in the lower band, which exhibit in-plane hyperbolicities, is wider than that for the HPhPs in the upper band of out-of-plane hyperbolicities. A polariton wavelength elongation up to 160% and a reduction of damping rate up to 35% are obtained. These findings can not only provide fundamental insights into manipulation of light by polaritonic crystals at nanoscale, but also open up new opportunities for tunable nanophotonic applications.

Published
2021

3. Controlling and focusing of in-plane hyperbolic phonon polaritons in {\alpha}-MoO3 with plasmonic antenna

Author

Zheng, Zebo, Jiang, Jingyao, Xu, Ningsheng, Wang, Ximiao, Huang, Wuchao, Ke, Yanlin, Chen, Huanjun, and Deng, Shaozhi

Subjects
Physics - Optics
Abstract

Hyperbolic phonon polaritons (HPhPs) sustained in van der Waals (vdW) materials exhibit extraordinary capabilities of confining long-wave electromagnetic fields to the deep subwavelength scale. In stark contrast to the uniaxial vdW hyperbolic materials such as hexagonal boron nitride (h-BN), the recently emerging biaxial hyperbolic materials such as {\alpha}-MoO3 and {\alpha}-V2O5 further bring new degree of freedoms in controlling light at the flatland, due to their distinctive in-plane hyperbolic dispersion. However, the controlling and focusing of such in-plane HPhPs are to date remain elusive. Here, we propose a versatile technique for launching, controlling and focusing of in-plane HPhPs in {\alpha}-MoO3 with geometrically designed plasmonic antennas. By utilizing high resolution near-field optical imaging technique, we directly excited and mapped the HPhPs wavefronts in real space. We find that subwavelength manipulating and focusing behavior are strongly dependent on the curvature of antenna extremity. This strategy operates effectively in a broadband spectral region. These findings can not only provide fundamental insights into manipulation of light by biaxial hyperbolic crystals at nanoscale, but also open up new opportunities for planar nanophotonic applications.

Published
2021

4. Polariton Waveguide Modes in Two-Dimensional Van der Waals Crystals: An Analytical Model and Correlative Scanning Near-Field Optical Microscopy Studies

Author

Sun, Fengsheng, Huang, Wuchao, Zheng, Zebo, Xu, Ningsheng, Ke, Yanlin, Zhan, Runze, Chen, Huanjun, and Deng, Shaozhi

Subjects
Physics - Optics, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Two-dimensional van der Waals (vdW) crystals can sustain various types of polaritons with strong electromagnetic confinements, making them highly attractive for the nanoscale photonic and optoelectronic applications. While extensive experimental and numerical studies are devoted to the polaritons of the vdW crystals, analytical models are sparse. Particularly, applying such a model to describe the polariton behaviors visualized by state-of-art near-field optical microscopy requires further investigation. Herein, we develop an analytical waveguide model to describe the polariton propagations in vdW crystals. The dispersion contours, dispersion relations, and electromagnetic field distributions of different polariton waveguide modes are derived. The model is verified by near-field optical imaging and numerical simulation of phonon polaritons in the {\alpha}-MoO3, a typical vdW biaxial crystals. The model can be extended to other types of polaritons in vdW crystals, thus allowing for describing and understanding their localized electromagnetic behaviors analytically.

Published
2019

5. A mid-infrared biaxial hyperbolic van der Waals crystal

Author

Zheng, Zebo, Xu, Ningsheng, Oscurato, Stefano Luigi, Tamagnone, Michele, Sun, Fengsheng, Jiang, Yinzhu, Ke, Yanlin, Chen, Jianing, Huang, Wuchao, Wilson, William L., Ambrosio, Antonio, Deng, Shaozhi, and Chen, Huanjun

Subjects
Physics - Optics
Abstract

Hyperbolic media have attracted much attention in the photonics community, thanks to their ability to confine light to arbitrarily small volumes and to their use for super-resolution applications. The 2D counterpart of these media can be achieved with hyperbolic metasurfaces, which support in-plane hyperbolic guided modes thanks to nanopatterns which, however, pose significant fabrication challenges and limit the achievable confinement. We show that thin flakes of the van der Waals material {\alpha}-MoO3 can support naturally in-plane hyperbolic polariton guided modes at mid-infrared frequencies without any patterning. This is possible because {\alpha}-MoO3 is a biaxial hyperbolic crystal, with three different Restrahlen bands, each for a different crystal axis. Our findings can pave the way towards new paradigm to manipulate and confine light in planar photonic devices.

Published
2018

10. Tailoring Beam Shape Using a Coplanar Quadrupole Focusing Structure in Carbon Nanotube Cold Cathode Electron Gun

Author

Wang, Lizhou, Zhang, Yu, Hong, Tianzeng, Wu, Yiting, Ke, Yanlin, and Deng, Shaozhi

Abstract

Carbon nanotubes (CNTs) cold cathode has excellent electron emission characteristics and showed its importance in vacuum electronic device applications. Facing various demand on electron beam with different devices, the cold cathode electron gun as a component for generating electron beam raises a challenge for controlling the beam which possess high-speed electrons due to the high driven field from a cold cathode. Here, a coplanar quadrupole focusing structure is proposed to adding in a CNT cold cathode electron gun to realize a multifunctional electron beam shape tailoring. In principle, the field emission electrons were first decelerated then adjusted by the focusing electrode modules to achieve multiple functions, including beam focusing, sheet beam adjusting, and beam shifting. In the experimental results, the area compression ratio of the electron beam was ~34.6; a round beam spot with a diameter of 2.76 mm was compressed to a sheet beam with a width of 0.15 mm; a beam position shifting was as large as 2.22 mm in radial cross section. This work demonstrates the feasibility of tailoring the beam shape of electron beam in a cold cathode gun according to the device application requirements.

Published
2023
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17. Controlling and focusing of in-plane hyperbolic phonon polaritons in ��-MoO3 with plasmonic antenna

Author

Zheng, Zebo, Jiang, Jingyao, Xu, Ningsheng, Wang, Ximiao, Huang, Wuchao, Ke, Yanlin, Chen, Huanjun, and Deng, Shaozhi

Subjects
Physics::Optics, FOS: Physical sciences, Optics (physics.optics)
Abstract

Hyperbolic phonon polaritons (HPhPs) sustained in van der Waals (vdW) materials exhibit extraordinary capabilities of confining long-wave electromagnetic fields to the deep subwavelength scale. In stark contrast to the uniaxial vdW hyperbolic materials such as hexagonal boron nitride (h-BN), the recently emerging biaxial hyperbolic materials such as ��-MoO3 and ��-V2O5 further bring new degree of freedoms in controlling light at the flatland, due to their distinctive in-plane hyperbolic dispersion. However, the controlling and focusing of such in-plane HPhPs are to date remain elusive. Here, we propose a versatile technique for launching, controlling and focusing of in-plane HPhPs in ��-MoO3 with geometrically designed plasmonic antennas. By utilizing high resolution near-field optical imaging technique, we directly excited and mapped the HPhPs wavefronts in real space. We find that subwavelength manipulating and focusing behavior are strongly dependent on the curvature of antenna extremity. This strategy operates effectively in a broadband spectral region. These findings can not only provide fundamental insights into manipulation of light by biaxial hyperbolic crystals at nanoscale, but also open up new opportunities for planar nanophotonic applications.

Published
2021
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18. Tunable Hyperbolic Phonon Polaritons in a Gradiently-Suspended Van Der Waals ��-MoO3

Author

Zheng, Zebo, Sun, Fengsheng, Huang, Wuchao, Chen, Xuexian, Ke, Yanlin, Zhan, Runze, Chen, Huanjun, and Deng, Shaozhi

Subjects
Physics::Optics, FOS: Physical sciences, Optics (physics.optics)
Abstract

Highly confined and low-loss hyperbolic phonon polaritons (HPhPs) sustained in van der Waals crystals exhibit outstanding capabilities of concentrating long-wave electromagnetic fields deep to the subwavelength region. Precise tuning on the HPhP propagation characteristics remains a great challenge for practical applications such as nanophotonic devices and circuits. Here, we show that by taking advantage of the varying air gaps in a van der Waals ��-MoO3 crystal suspended gradiently, it is able to tune the wavelengths and dampings of the HPhPs propagating inside the ��-MoO3. The results indicate that the dependences of polariton wavelength on gap distance for HPhPs in lower and upper Reststrahlen bands are opposite to each other. Most interestingly, the tuning range of the polariton wavelengths for HPhPs in the lower band, which exhibit in-plane hyperbolicities, is wider than that for the HPhPs in the upper band of out-of-plane hyperbolicities. A polariton wavelength elongation up to 160% and a reduction of damping rate up to 35% are obtained. These findings can not only provide fundamental insights into manipulation of light by polaritonic crystals at nanoscale, but also open up new opportunities for tunable nanophotonic applications.

Published
2021
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19. Tunable Hyperbolic Phonon Polaritons in a Suspended van der Waals α‐MoO3 with Gradient Gaps.

Author

Zheng, Zebo, Sun, Fengsheng, Xu, Ningsheng, Huang, Wuchao, Chen, Xuexian, Ke, Yanlin, Zhan, Runze, Chen, Huanjun, and Deng, Shaozhi

Subjects
POLARITONS, PHONONS, ELECTROMAGNETIC fields, CRYSTALS, WAVELENGTHS
Abstract

Highly confined and low‐loss hyperbolic phonon polaritons (HPhPs) sustained in van der Waals crystals exhibit outstanding potential to concentrate the long‐wave electromagnetic fields deep into the subwavelength region. However, precise tuning on the HPhP propagation characteristics is a critical challenge to facilitate its practical applications in nanophotonic devices and circuits. This study, by taking advantage of the varying air gaps in a suspended van der Waals α‐MoO3 crystal, shows the feasibility to tune wavelength and damping rate of the HPhPs propagating inside the α‐MoO3. The results indicate that the dependence of polariton wavelength on the gap distance for HPhPs in lower and upper Reststrahlen bands contradict each other. Most interestingly, the tuning range of the polariton wavelengths for HPhPs in the lower band, which exhibits in‐plane hyperbolicity, is wider than that for HPhPs in the upper band which exhibits out‐of‐plane hyperbolicity. A polariton wavelength elongation of up to 160% and a reduction in the damping rate up to 35% is recorded. These findings can not only provide fundamental insight into the nanoscale manipulation of light by polaritonic crystals, but also open up new opportunities for tunable nanophotonic applications. [ABSTRACT FROM AUTHOR]

Published
2022
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25. A mid-infrared biaxial hyperbolic van der Waals crystal

Author

Zheng, Zebo, primary, Xu, Ningsheng, additional, Oscurato, Stefano L., additional, Tamagnone, Michele, additional, Sun, Fengsheng, additional, Jiang, Yinzhu, additional, Ke, Yanlin, additional, Chen, Jianing, additional, Huang, Wuchao, additional, Wilson, William L., additional, Ambrosio, Antonio, additional, Deng, Shaozhi, additional, and Chen, Huanjun, additional

Published
2019
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31. Resonance Coupling in Silicon Nanosphere–J-Aggregate Heterostructures

Author

Wang, Hao, primary, Ke, Yanlin, additional, Xu, Ningsheng, additional, Zhan, Runze, additional, Zheng, Zebo, additional, Wen, Jinxiu, additional, Yan, Jiahao, additional, Liu, Pu, additional, Chen, Jun, additional, She, Juncong, additional, Zhang, Yu, additional, Liu, Fei, additional, Chen, Huanjun, additional, and Deng, Shaozhi, additional

Published
2016
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33. Chemically-doped graphene with improved surface plasmon characteristics: an optical near-field study

Author

Zheng, Zebo, primary, Wang, Weiliang, additional, Ma, Teng, additional, Deng, Zexiang, additional, Ke, Yanlin, additional, Zhan, Runze, additional, Zou, Qionghui, additional, Ren, Wencai, additional, Chen, Jun, additional, She, Juncong, additional, Zhang, Yu, additional, Liu, Fei, additional, Chen, Huanjun, additional, Deng, Shaozhi, additional, and Xu, Ningsheng, additional

Published
2016
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