Reflective grating-coupled structure improves the detection efficiency of THz array detectors

Peng Xiao,Chengtao Jiang,Shimin Zhai,Peiheng Wu,Xuecou Tu,Danfeng Pan,Xiaoqing Jia,Zhou Jiang,Jian Chen,Lin Kang

doi:10.1038/s41598-018-26204-y

Peng Xiao, Chengtao Jiang + Show 8 more

Open Access

https://doi.org/10.1038/s41598-018-26204-y

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Journal: Scientific Reports	Publication Date: May 23, 2018
Citations: 7	License type: open-access

Affiliation: Nanjing University

Abstract

A reflective grating-coupled structure on the silicon substrate was designed to improve the detection efficiency of terahertz detectors for the frequency ranging from 0.26 THz to 0.36 THz. By using finite difference time domain (FDTD) solutions, the simulation and optimized design of the grating-coupled structure were carried out. The results showed that the signal was effectively reflected and diffracted by the reflective grating-coupled structure which significantly enhanced the electric field in the place of the detector. The maximum electric field can be increased by 2.8 times than that of the Fabry-Perot resonator. To verify the design results, the reflective grating-coupled structure was applied in the preparation of the Nb5N6 array detector chip and compared with the Nb5N6 array detector chip with the F-P resonator. The results showed that the maximum voltage responsivity of the Nb5N6 detector with the reflective grating-coupled structure was 2 times larger than the Nb5N6 detector with the F-P resonator. It indicates that the reflective grating-coupled structure can efficiently improve the detection efficiency of THz detectors.

Highlights

Terahertz (THz) detectors, which has attracted great attention and been applied in many fields such as security check, medical imaging and components identification[1,2], play a very important role in the field of the THz (0.1 THz~10 THz) technology
The detection efficiency can be improved by using the sub-wavelength periodic structure to regulate the phase and amplitude of the signal[16,17,18,19,20]
For the reflective grating-coupled structure, a portion of the incidence signal is reflected at the substrate surface, and the resident signals transmit into the silicon substrate

Summary

Introduction

Terahertz (THz) detectors, which has attracted great attention and been applied in many fields such as security check, medical imaging and components identification[1,2], play a very important role in the field of the THz (0.1 THz~10 THz) technology. For THz detector prepared by microfabrication, the size of the focused Gaussian beam waist is much larger than that of the detector Such limitation leads to a low signal coupling efficiency. Many coupling structures have been applied to improve the signal coupling efficiency of THz detector, for example, the extended hemispherical lens[8], diffractive lens[9], F-P air cavity[10,11,12] and metal grating coupler[13,14], etc. According to Huygens principle, flat optics can mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers[15] It can create smaller and more optically efficient products, and at the same time, are gradually used in THz band. The experimental results verified that with the reflective grating-coupled structure, the maximum voltage responsivity of Nb5N6 array detector was 2 times larger than that of detectors array with a F-P resonator

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Conclusion