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Fu T, Zhang RY, Jia S, Chan CT, Wang S. Near-Field Spin Chern Number Quantized by Real-Space Topology of Optical Structures. PHYSICAL REVIEW LETTERS 2024; 132:233801. [PMID: 38905648 DOI: 10.1103/physrevlett.132.233801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Accepted: 05/01/2024] [Indexed: 06/23/2024]
Abstract
The Chern number has been widely used to describe the topological properties of periodic structures in momentum space. Here, we introduce a real-space spin Chern number for the optical near fields of finite-sized structures. This new spin Chern number is intrinsically quantized and equal to the structure's Euler characteristic. The relationship is robust against continuous deformation of the structure's geometry and is irrelevant to the specific material constituents or external excitation. Our Letter enriches topological physics by extending the Chern number to real space, opening exciting possibilities for exploring the real-space topological properties of light.
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Ni X, Liu Y, Lou B, Zhang M, Hu EL, Fan S, Mazur E, Tang H. Three-Dimensional Reconfigurable Optical Singularities in Bilayer Photonic Crystals. PHYSICAL REVIEW LETTERS 2024; 132:073804. [PMID: 38427898 DOI: 10.1103/physrevlett.132.073804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 01/12/2024] [Indexed: 03/03/2024]
Abstract
Metasurfaces and photonic crystals have revolutionized classical and quantum manipulation of light and opened the door to studying various optical singularities related to phases and polarization states. However, traditional nanophotonic devices lack reconfigurability, hindering the dynamic switching and optimization of optical singularities. This paper delves into the underexplored concept of tunable bilayer photonic crystals (BPhCs), which offer rich interlayer coupling effects. Utilizing silicon nitride-based BPhCs, we demonstrate tunable bidirectional and unidirectional polarization singularities, along with spatiotemporal phase singularities. Leveraging these tunable singularities, we achieve dynamic modulation of bound-state-in-continuum states, unidirectional guided resonances, and both longitudinal and transverse orbital angular momentum. Our work paves the way for multidimensional control over polarization and phase, inspiring new directions in ultrafast optics, optoelectronics, and quantum optics.
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Affiliation(s)
- Xueqi Ni
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Yuan Liu
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Beicheng Lou
- Department of Applied Physics and Ginzton Laboratory, Stanford University, Stanford, California 94305, USA
| | - Mingjie Zhang
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Evelyn L Hu
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Shanhui Fan
- Department of Applied Physics and Ginzton Laboratory, Stanford University, Stanford, California 94305, USA
| | - Eric Mazur
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Haoning Tang
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
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Lu J, Ginis V, Lim SWD, Capasso F. Helicity and Polarization Gradient Optical Trapping in Evanescent Fields. PHYSICAL REVIEW LETTERS 2023; 131:143803. [PMID: 37862648 DOI: 10.1103/physrevlett.131.143803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 09/13/2023] [Indexed: 10/22/2023]
Abstract
Optical traps using nonconservative forces instead of conservative intensity-gradient forces expand the trap parameter space. Existing traps with nonconservative helicity-dependent forces are limited to chiral particles and fields with helicity gradients. We relax these constraints by proposing helicity and polarization gradient optical trapping of achiral particles in evanescent fields. We further propose an optical switching system in which a microsphere is trapped and optically manipulated around a microfiber using polarization gradients. Our Letter deepens the understanding of light-matter interactions in polarization gradient fields and expands the range of compatible particles and stable trapping fields.
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Affiliation(s)
- Jinsheng Lu
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, Massachusetts 02138, USA
| | - Vincent Ginis
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, Massachusetts 02138, USA
- Data Lab and Applied Physics, Vrije Universiteit Brussel, 1050 Brussel, Belgium
| | - Soon Wei Daniel Lim
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, Massachusetts 02138, USA
| | - Federico Capasso
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, Massachusetts 02138, USA
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Lim SWD, Park JS, Kazakov D, Spägele CM, Dorrah AH, Meretska ML, Capasso F. Point singularity array with metasurfaces. Nat Commun 2023; 14:3237. [PMID: 37277345 DOI: 10.1038/s41467-023-39072-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Accepted: 05/23/2023] [Indexed: 06/07/2023] Open
Abstract
Phase singularities are loci of darkness surrounded by monochromatic light in a scalar field, with applications in optical trapping, super-resolution imaging, and structured light-matter interactions. Although 1D singular structures, like optical vortices, are common due to their robust topological properties, uncommon 0D (point) and 2D (sheet) singularities can be generated by wavefront-shaping devices like metasurfaces. With the design flexibility of metasurfaces, we deterministically position ten identical point singularities using a single illumination source. The phasefront is inverse-designed using phase-gradient maximization with an automatically-differentiable propagator and produces tight longitudinal intensity confinement. The array is experimentally realized with a TiO2 metasurface. One possible application is blue-detuned neutral atom trap arrays, for which this field would enforce 3D confinement and a potential depth around 0.22 mK per watt of incident laser power. We show that metasurface-enabled point singularity engineering may significantly simplify and miniaturize the optical architecture for super-resolution microscopes and dark traps.
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Affiliation(s)
- Soon Wei Daniel Lim
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, MA, 02138, USA.
| | - Joon-Suh Park
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, MA, 02138, USA
- Nanophotonics Research Center, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Dmitry Kazakov
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, MA, 02138, USA
| | - Christina M Spägele
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, MA, 02138, USA
| | - Ahmed H Dorrah
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, MA, 02138, USA
| | - Maryna L Meretska
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, MA, 02138, USA
| | - Federico Capasso
- Harvard John A. Paulson School of Engineering and Applied Sciences, 9 Oxford Street, Cambridge, MA, 02138, USA
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