Giant optical anisotropy of WS2flakes in the visible region characterized by Au substrate assisted near-field optical microscopy

Nan Deng; Hua Long; Kun Wang; Xiaobo Han; Bing Wang; Kai Wang; Peixiang Lu

doi:10.1088/1361-6528/ac6c96

Giant optical anisotropy of WS₂flakes in the visible region characterized by Au substrate assisted near-field optical microscopy

Nanotechnology. 2022 May 31;33(34). doi: 10.1088/1361-6528/ac6c96.

Authors

Nan Deng¹, Hua Long¹, Kun Wang¹, Xiaobo Han², Bing Wang¹, Kai Wang¹, Peixiang Lu^{1

2

3}

Affiliations

¹ Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
² Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology, Wuhan 430205, People's Republic of China.
³ Optics Valley Laboratory, Wuhan 430074, People's Republic of China.

PMID: 35508119
DOI: 10.1088/1361-6528/ac6c96

Abstract

Transition metal dichalcogenides (TMD) have attracted considerable attention in the field of photonic integrated circuits due to their giant optical anisotropy. However, on account of their inherent loss in the visible region and the difficulty of measuring high refractive index materials, near-field characterizations of the optical anisotropy of TMD in the visible region have inherent experimental difficulties. In this work, we present a systematical characterization of the optical anisotropy in tungsten disulfide (WS₂) flakes by using scattering-type scanning near-field optical microscopy (s-SNOM) excited at 671 nm. Transverse-electric and transverse-magnetic (TM) waveguide modes can be excited in WS₂flakes with suitable thickness, respectively. With the assistance of the Au substrate, the contrast of the near-field fringes is enhanced in comparison with the SiO₂substrate. By combining waveguide mode near-field imaging and theoretical calculations, the in-plane and out-of-plane refractive indexes of WS₂are determined to be 4.96 and 3.01, respectively, indicating a high birefringence value up to 1.95. This work offers experimental evidence for the potential application of WS₂in optoelectronic integrated circuits in the visible region.

Keywords: WS2 flakes; near-field characterizations; optical anisotropy; visible-region waveguides.