Browsing by Author "Liang, Wei-Yun"

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Chiral Second-Harmonic Generation from Monolayer WS2/Aluminum Plasmonic Vortex Metalens
(2020-04-08)
Guo, Wan-Ping
;
Liang, Wei-Yun
;
Cheng, Chang-Wei
;
Wu, Wei-Lin
;
Wang, Yen-Ting
Two-dimensional spiral plasmonic structures have emerged as a versatile approach to generate near-field vortex fields with tunable topological charges. We demonstrate here a far-field approach to observe the chiral second-harmonic generation (SHG) at designated visible wavelengths from a single plasmonic vortex metalens. This metalens comprises an Archimedean spiral slit fabricated on atomically flat aluminum epitaxial film, which allows for precise tuning of plasmonic resonances and subsequent transfer of two-dimensional materials on top of the spiral slit. The nonlinear optical measurements show a giant SHG circular dichroism. Furthermore, we have achieved an enhanced chiral SHG conversion efficiency (about an order of magnitude greater than the bare aluminum lens) from monolayer tungsten disulfide (WS2)/aluminum metalens, which is designed at the C-exciton resonance of WS2. Since the C-exciton is not a valley exciton, the enhanced chiral SHG in this hybrid system originates from the plasmonic vortex field-enhanced SHG under the optical spin-orbit interaction.
High optical nonlinearity in low-dimensional halide perovskite polycrystalline films
(2020-08-17)
Liang, Wei-Yun
;
Liu, Fangzhou
;
Lu, Yu-Jung
;
Popovic, Jasminka
;
Djurisic, Aleksandra
The nonlinear optical properties of low-dimensional polycrystalline halide perovskite films consisting of ethylammonium (EA) and butylammonium (BA) cations are investigated using Z-scan technique. Across the band-edge, two-dimensional (BA)(2)PbI4 exhibits a transition from saturable absorption (SA) to reverse-SA and its nonlinear absorption and nonlinear refractive index are much smaller than those of bulk counterparts. Meanwhile, EAPbI(3) with one-dimensionality of the inorganic structure shows the SA behavior both above and below band-edge and the estimated nonlinear optical parameters of polycrystalline EAPbI(3) are comparable to those of single-crystalline ones, attributed to high dielectric contrast between the inorganic and organic elements in one-dimensional structures. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Plasmonic enhancement and control of optical nonlinearity in monolayer WS2
(2018-01-01)
Liang, Wei-Yun
;
Ahn, Hyeyoung
;
Sang, Yungang
;
Wang, Yanrong
;
Shi, Jinwei
A giant SHG enhancement is achieved from monolayer-WS2 incorporated onto 2D plasmonic metasurfaces (Ag-nanogroove-grating) in resonance with the excitonic resonance of monolayer-WS2. An optical encoding technique is demonstrated based on plasmonic manipulation of SHG polarization.
Plasmonic Enhancement and Manipulation of Optical Nonlinearity in Monolayer Tungsten Disulfide
(2018-10-01)
Shi, Jinwei
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Liang, Wei-Yun
;
Raja, Soniya S.
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Sang, Yungang
;
Zhang, Xin-Quan
Monolayer transition metal dichalcogenides (TMDCs) have large second-order optical nonlinearity owing to broken inversion symmetry in two-dimensional (2D) crystals. However, despite the strong light-matter coupling in monolayer TMDCs, their nonlinear responses are ultimately limited by subnanometer thickness. Here, a dramatic enhancement of the second-harmonic generation (SHG) is achieved from monolayer tungsten disulfide (WS2) incorporated onto a 2D silver (Ag) nanogroove grating with subwavelength pitch. By tuning surface plasmon mode and second-harmonic frequency in resonance with the C exciton in WS2, a large SHG enhancement factor (approximate to 400) and a large conversion efficiency (approximate to 2.0 x 10(-5)) can be obtained. Furthermore, the azimuthal angle dependence of polarized SHG from monolayer WS2 can be manipulated by the nanogroove plasmonic mode. Based on this property, a polarization-modulated optical encoding technique is demonstrated. The results suggest that 2D TMDC-plasmonic hybrid metasurface structures can provide an ideal integration platform for on-chip nonlinear photonics and plasmonics.