Valley-polarized topological states of light allow for robust waveguiding, which has been demonstrated for transverse-electric modes in THz and near-infrared regions of the spectrum. As the topological protection relies on guiding the light via a highly structured surface, direct imaging of the photonic modes at subunit cell resolution is of high interest but challenging, particularly for transverse-magnetic modes. Here, we report mapping the transverse-magnetic modes in a valley photonic crystal waveguide using scattering-type scanning near-field optical microscopy at the optical telecom C-band wavelength. The waveguide based on a triangular air-hole motif with broken inversion symmetry is fabricated from the suspended germanium layer. We observed the launching and guiding of the transverse-magnetic edge mode along the boundary between topologically distinct domains with opposite valley Chern indices. These results are supported by theoretical simulations and provide insight into the design and use of topological protected states for applications in densely integrated optical telecommunication devices.
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Near-field mapping of the edge mode of a topological valley slab waveguide at λ = 1.55 μm
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11 May 2020
Research Article|
May 13 2020
Near-field mapping of the edge mode of a topological valley slab waveguide at λ = 1.55 μm

Alexander M. Dubrovkin
;
Alexander M. Dubrovkin
a)
1
Centre for Disruptive Photonic Technologies, TPI, Nanyang Technological University
, 637371 Singapore
2
School of Physical and Mathematical Sciences, Nanyang Technological University
, 637371 Singapore
a)Author to whom correspondence should be addressed: dubrovkin@ntu.edu.sg
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Udvas Chattopadhyay;
Udvas Chattopadhyay
2
School of Physical and Mathematical Sciences, Nanyang Technological University
, 637371 Singapore
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Bo Qiang;
Bo Qiang
1
Centre for Disruptive Photonic Technologies, TPI, Nanyang Technological University
, 637371 Singapore
3
Centre for OptoElectronics and Biophotonics, School of Electrical and Electronic Engineering, Nanyang Technological University
, 639798 Singapore
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Oleksandr Buchnev;
Oleksandr Buchnev
4
Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton
, Southampton SO17 1BJ, United Kingdom
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Qi Jie Wang
;
Qi Jie Wang
1
Centre for Disruptive Photonic Technologies, TPI, Nanyang Technological University
, 637371 Singapore
2
School of Physical and Mathematical Sciences, Nanyang Technological University
, 637371 Singapore
3
Centre for OptoElectronics and Biophotonics, School of Electrical and Electronic Engineering, Nanyang Technological University
, 639798 Singapore
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Yidong Chong;
Yidong Chong
b)
1
Centre for Disruptive Photonic Technologies, TPI, Nanyang Technological University
, 637371 Singapore
2
School of Physical and Mathematical Sciences, Nanyang Technological University
, 637371 Singapore
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Nikolay I. Zheludev
Nikolay I. Zheludev
b)
1
Centre for Disruptive Photonic Technologies, TPI, Nanyang Technological University
, 637371 Singapore
2
School of Physical and Mathematical Sciences, Nanyang Technological University
, 637371 Singapore
4
Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton
, Southampton SO17 1BJ, United Kingdom
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a)Author to whom correspondence should be addressed: dubrovkin@ntu.edu.sg
b)
Electronic addresses: yidong@ntu.edu.sg and niz@orc.soton.ac.uk
Appl. Phys. Lett. 116, 191105 (2020)
Article history
Received:
February 10 2020
Accepted:
April 20 2020
Connected Content
A companion article has been published:
Crystal topological waveguides allow for the visualization of nanophotonic light flow
Citation
Alexander M. Dubrovkin, Udvas Chattopadhyay, Bo Qiang, Oleksandr Buchnev, Qi Jie Wang, Yidong Chong, Nikolay I. Zheludev; Near-field mapping of the edge mode of a topological valley slab waveguide at λ = 1.55 μm. Appl. Phys. Lett. 11 May 2020; 116 (19): 191105. https://doi.org/10.1063/5.0004390
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