Tailoring topological edge states with photonic crystal nanobeam cavities

Yongkang Gong,Stephan Wong,Anthony J Bennett,Sang Soon Oh,Liang Guo

doi:10.1038/s41598-020-79915-6

Yongkang Gong, Stephan Wong + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-79915-6

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Journal: Scientific Reports	Publication Date: Jan 13, 2021
Citations: 7	License type: open-access

Affiliation: Cardiff University

Abstract

The realization of topological edge states (TESs) in photonic systems has provided unprecedented opportunities for manipulating light in novel manners. The Su–Schrieffer–Heeger (SSH) model has recently gained significant attention and has been exploited in a wide range of photonic platforms to create TESs. We develop a photonic topological insulator strategy based on SSH photonic crystal nanobeam cavities. In contrast to the conventional photonic SSH schemes which are based on alternately tuned coupling strength in one-dimensional lattice, our proposal provides higher flexibility and allows tailoring TESs by manipulating mode coupling in a two-dimensional manner. We reveal that the proposed hole-array based nanobeams in a dielectric membrane can selectively tailor single or double TESs in the telecommunication region by controlling the coupling strength of the adjacent SSH nanobeams in both transverse and axial directions. Our finding provides an additional degree of freedom in exploiting the SSH model for integrated topological photonic devices and functionalities based on the well-established photonic crystal nanobeam cavity platforms.

Highlights

Properties, and have found tremendous photonic integrated circuit applications such as sensors52, nanolasers[53,54], optical switches[55], electro-optical modulators[56] and single-photon sources[57,58,59] in optical systems, nonlinear mixing[60] and wavelength conversion[61] in opto-mechanical systems, and thermal management in opto-thermal systems[62,63]
Since the topological property of the proposed SSH nanobeam structure arises from the alternating coupling strength between the adjacent nanobeams, we first investigate the optical coupling characteristic of two identical nanobeams, as schematically depicted in Fig. 1a, where the two nanobeams have transverse spacing of d1 and axial shift of d2 with each nanobeam incorporating six air holes in the reflector sections and nine air holes in the taper section
The hole-to-hole spacing in the two reflector sections is the same but reduces gradually from both sides to the center of the taper section to form an optical cavity

Summary

Introduction

Properties, and have found tremendous photonic integrated circuit applications such as sensors52, nanolasers[53,54], optical switches[55], electro-optical modulators[56] and single-photon sources[57,58,59] in optical systems, nonlinear mixing[60] and wavelength conversion[61] in opto-mechanical systems, and thermal management in opto-thermal systems[62,63]. We investigate the wavelength splitting of the resonance modes of the two coupled nanobeams when their axial shift d2 changes at a fixed transverse spacing d1 (see Fig. 1a).

Results

Conclusion