Surface enhancement of THz wave by coupling a subwavelength LiNbO3 slab waveguide with a composite antenna structure

Qi Zhang,Wenjuan Zhao,Chongpei Pan,Jiwei Qi,Qiang Wu,Ride Wang,Shibiao Wang,Yao Lu,Jingjun Xu

doi:10.1038/s41598-017-17712-4

Qi Zhang, Wenjuan Zhao + Show 7 more

Open Access

https://doi.org/10.1038/s41598-017-17712-4

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Journal: Scientific Reports	Publication Date: Dec 1, 2017
Citations: 7	License type: open-access

Affiliation: Nankai University, Shanxi University

Abstract

Highly intense terahertz electromagnetic field and efficiently surface localized terahertz field in subwavelength volumes are of vital importance for terahertz photonics integration, also will greatly accelerate the development for integrated applications in biochemical sensing, imaging, terahertz spectroscopy, enhancement of nonlinear effects and even quantum research. In this paper, we achieved large terahertz field enhancement and surface field localization through depositing a pair of Au composite antennas on a LiNbO3 subwavelength slab waveguide, which can serve as an excellent on-chip platform for terahertz research and application. The antennas consist of two opposing tip-to-tip triangles separated by a gap, and each triangle combines with a strip antenna. Time-resolved imaging and finite-difference time-domain method were used to resolve the characteristics of the designed antennas experimentally and simulatively. Through these methods, we demonstrated outstanding abilities of the platform: leading to a large electric field enhancement, concentrating almost full terahertz energy on the waveguide’s surface when they are resonant with the terahertz waves and tunable resonant frequency. These abilities make the subwavelength waveguide coupling with the composite antennas be able to sever as a good integrated device to identify terahertz-sensitive small objects, or an excellent platform to terahertz spectroscopy and quantum research.

Highlights

Chip-scale photonic integrated circuits (PICs) are extremely necessary for applications such as ultra-fast telecommunications and integrated biochemical sensors[1]
Correspondence and requests for materials should be addressed to J.Q. or Q.W. www.nature.com/scientificreports/. It is challenging for simple LN waveguide to sever as a sensing or other utility applications, just like a PICs platform do, since the field intensity of the available THz source generated by LN slab is still low[22]
In this paper we propose to use a pair of Au dipole antennas coupled to the subwavelength waveguide, which can efficiently convert propagating optical radiation to localized energy[26], to provide large field enhancement and surface field localization

Summary

Introduction

Chip-scale photonic integrated circuits (PICs) are extremely necessary for applications such as ultra-fast telecommunications and integrated biochemical sensors[1]. A LN slab, when its thickness becomes comparable to or less than the THz wavelength, can serve as a subwavelength planar waveguide and provide a platform for THz processing, since the generation, propagation, detection, and control can be fully integrated in one sample[14,15] This on-chip platform has achieved effects such as THz antenna[16], photonic crystals[17], band-stop filer[18], THz microcavities[19], THz cloak[20] and even designing research for THz metamaterials and negative refractive materials[21]. This opens the door for the sensing application, and for THz spectroscopic analysis[30] and interfacing the LN slab with THz devices, even research of electronic transitions in nanostructures[31,32] like quantum wells or quantum dots[33]

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