Recently, the team of Prof. Li Jiafang, Zhang Xiangdong and Yao Yugui, School of Physics, BIT, together with Researcher Li Junjie and Gu Changzhi, Institute of Physics, Chinese Academy of Sciences (CAS), and Prof. Nicholas X. Fang, Massachusetts Institute of Technology (MIT), have developed a new technology for on-chip nano-opto-electromechanical control. By using electrostatic force to drive the reversible deformation of nano-kirigami, the electromechanical control of optical resonance under sub-micron pixels is realized, and the on-chip tuning function of optical chirality is demonstrated. The innovation was published in Nature Communications (IF: 12.121), a sub Journal of Nature.

With the development of nano-manufacturing technology, the combination of micro-electro-mechanical systems (MEMS) and nano-photonic technology has formed the international cutting-edge nano-opto-electro-mechanical systems (NOEMS), which is widely used in information, electronics, medicine, industry, automobile, aerospace systems. However, there is a balance between the miniaturization of the reconfigurable element and the improvement of the modulation depth (usually determined by the spatial displacement), which limits the design of NOEMS structures to a few options such as cantilever beams and ultra-thin films. This limits the contrast of the opto-electromechanical modulation, and leads to technical bottlenecks in the spatial light modulation of sub-micron pixels (eg.: the pixel size of the DMD chip is limited to more than 5 microns and the modulation frequency is below 40kHz). In order to solve these problems, Prof. Li Jiafang and his team invented a nano-kirigami technology [Science Advances 4, eaat4436 (2018)] in 2018, which can flexibly and automatically prepare a variety of novel three-dimensional and quasi-three-dimensional nanostructures [Light- Sci. Appl. 9, 75 (2020)], and has a mechanically reconfigurable function [Adv. Mater. 32, 1907077 (2020)]. After a long period of theoretical and experimental exploration, Prof. Li proposed a nano-kirigami reversible deformation NOEMS driven by electrostatic force. As shown in Fig. 1-a, b, by applying different voltages between the metal nano pattern at the top and the silicon substrate at the bottom, electrostatic force can be used to achieve large-area, pixelated, in-situ, and reversible three-dimensional nano-kirigami deformation under large modulation depth (Fig. 1-c-f).

Fig.1: (a-c) Principle diagram of nano-kirigami deformation driven by electrostatic force;

(d) Simulation diagram of structural element before and after deformation;

(e, f) The SEM images of 2D structure of four arm windmill array before applied voltage and 3D structure after applying voltage (Scale: 1μm)

Nano-scale on-chip reconfigurable optical modulation is one of the most important challenges faced by applications such as photonic integration, metasurfaces, and optical metamaterials. Prof. Li proposed this kind of nano-opto-electromechanical system based on nano-kirigami, which can not only generate huge out of plane displacement by driving the deformation element with electrostatic force, but also easily stimulate optical resonance. By flexibly designing and optimizing nano-kirigami patterns, the team has achieved broadband dynamic modulation in the visible light band (Fig. 2-a, b) and optical resonance control in the near-infrared band (Fig. 2-c, d), and the pixel size can be reduced to 0.975 μm. In addition, the dynamic tuning of optical chirality is also realized in the near-infrared band (Fig. 2-e), and theoretical results show that the modulation speed of the system can reach over 10MHz (Fig. 2-f).

Moreover, this reconfigurable nano-opto-electromechanical system is compatible with conventional CMOS technology, which can further realize miniaturization and large-area fabrication. At the same time, the nano-kirigami deformation principle and the vertical driving mechanism of the electrostatic field proposed in this research can also be extended to other material systems and reconfigurable optical platforms. This small-size, high-contrast, reconfigurable optical nano-kirigami technology provides a new design method and technical route for high-speed, high-resolution spatial optical modulation, and provides a novel solution for the realization of new NOEMS devices.

Fig. 2: (a, b) Broadband tuning characteristics of windmill structure in visible light band;

(c, d) Optical resonance dynamic tuning characteristics of spiral and cross-line structures in the near-infrared band;

(e) The circular dichroism before and after the structural deformation of the three-arm windmill is measured experimentally;

(f) The calculated intrinsic mechanical resonance frequencies of the two kirigami structures under different driving voltages in (a) and (c), whose modulation frequency can reach 5-14 MHz

This research overcomes the disadvantages of the first-generation nano-kirigami technology, relying on self-supporting film/window substrates with low large-area preparation efficiency and the lack of rapid dynamic control functions, and realizes the second-generation of electromechanical reconfigurable nano-kirigami technology, which provides a novel platform for the physical and application research of on-chip reconfigurable optoelectronic devices, such as nano-photonics, spatial light modulation, opto-mechanics, MEMS, and NOEMS. Chen Shanshan (doctor, BIT), as well as Liu Zhiguang (post-doctor, SUSTech-MIT), Du Huifeng (doctor, MIT) and Tang Chengchun (engineer, Alibaba DAMO Academy) is the co-first-author of the paper, and Prof. Li Jiafang, Researcher Li Junjie and Prof. Nicholas X. Fang are the co-corresponding authors. The research team would like to thank Prof. Li Zhiyuan, South China University of Technology, Prof. Lu Ling, Institute of Physics, CAS, Key Laboratory of Optical Physics and Laboratory of Microfabrication, CAS, and Analysis&Testing Center, BIT, etc. for their support and help. Special thanks would be given to Mr. Wu Guangheng, Institute of physics, CAS, for his help in electrical testing. Besides, this research is supported by the National Natural Science Foundation of China, the National Key R&D Program of China, Guangdong Provincial Key R&D Program, and Beijing Municipal Natural Science Foundation, etc..

Paper information (# is the co-fist-author; * is the co-corresponding author):

Shanshan Chen#, Zhiguang Liu#, Huifeng Du#, Chengchun Tang#, Chang-Yin Ji, Baogang Quan, Ruhao Pan, Lechen Yang, Xinhao Li, Changzhi Gu, Xiangdong Zhang, Yugui Yao, Junjie Li*, Nicholas X. Fang*, and Jiafang Li*, “Electromechanically reconfigurable optical nano-kirigami”, Nature Communications 12, 1299 (2021).

Paper Link:

https://www.nature.com/articles/s41467-021-21565-x

Introduction to the first generation of nano-kirigami technology: http://www.nanokirigami.com