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

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

https://www.nature.com/articles/s41598-018-26204-y

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.

Abstract-Investigation of antenna-coupled Nb5N6 microbolometer THz detector with substrate resonant cavity

Xuecou Tu, Chengtao Jiang, Peng Xiao, Lin Kang, Shimin Zhai, Zhou Jiang, Run Feng Su, Xiaoqing Jia, Labao Zhang, Jian Chen, and Peiheng Wu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-7-8990

Fabricating resonant cavities with conventional methods to improve the coupling efficiency of a detector in the terahertz (THz) region is difficult for the wavelength is too long. Here, we propose a solution by using the substrate cavity effect given that the substrate wavelength and thickness of the preparation device are in the same order. The planar dipole antenna-coupled Nb5N6 microbolometers with different substrate thicknesses were fabricated. The interference effect of the substrate cavity on the optical voltage response of the detector is analyzed experimentally and theoretically. The experimental results show that the optical response of the detector is determined by the length of the substrate cavity. Thus, the THz devices with different detection frequencies can be designed by changing the substrate cavity length. Furthermore, on the basis of this substrate cavity effect, an asymmetric coupled Fabry-Pérot (FP) cavity is constituted by simply placing a movable metallic planar mirror at the backside of the Si substrate. The incident THz radiation on the Nb5N6 microbolometer can be effectively manipulated by changing the substrate-mirror distance to modulate the phase relation between the reflect wave and the incident wave. The distinct radiation control can be observed, and the experiments can be well explained by numerically analyzing the responsivity dynamics that highlights the role of the FP cavity effect during radiation. All of the results discussed here can be extended to a broad range of frequency and other type of THz detectors.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Electrically tunable superconducting terahertz metamaterial with low insertion loss and high switchable ratios

Chun Li1, Caihong Zhang1,a), Guoliang Hu1, Gaochao Zhou1, Shoulu Jiang1, Chengtao Jiang1, Guanghao Zhu1, Biaobing Jin1,b), Lin Kang1,Weiwei Xu1, Jian Chen1 and Peiheng Wu1


1 Research Institute of Superconductor Electronics (RISE), School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
a) Electronic mail: chzhang@nju.edu.cn
b) Electronic mail: bbjin@nju.edu.cn
Appl. Phys. Lett. 109, 022601 (2016); http://dx.doi.org/10.1063/1.4955454

http://scitation.aip.org/content/aip/journal/apl/109/2/10.1063/1.4955454

With the emergence and development of artificially structured electromagnetic materials, active terahertz (THz) metamaterial devices have attracted significant attention in recent years. Tunability of transmission is desirable for many applications. For example, short-range wireless THz communications and ultrafast THz interconnects require switches and modulators. However, the tunable range of transmission amplitude of existing THz metamaterial devices is not satisfactory. In this article, we experimentally demonstrate an electrically tunable superconducting niobium nitride metamaterial device and employ a hybrid coupling model to analyze its optical transmission characteristics. The maximum transmission coefficient at 0.507 THz is 0.98 and decreases to 0.19 when the applied voltage increases to 0.9 V. A relative transmittance change of 80.6% is observed, making this device an efficient narrowband THz switch. Additionally, the frequency of the peak is red shifted from 0.507 to 0.425 THz, which means that the device can be used to select the frequency. This study offers an alternative tuning method to existing optical, thermal, magnetic-field, and electric-field tuning, delivering a promising approach for designing active and miniaturized THz devices.