Microfluidic integrated metamaterials for active terahertz photonics

Metamaterials, composed of periodic arrangements of artificial sub-wavelength unit cells, have aroused great attention in the scientific community due to their novel optical properties. The well-known basic block is plasmonic split-ring resonators (SRRs). Based on the design of the geometric configuration, they exhibit excellent modulation performance for terahertz waves (THz). However, the fixed structures of SRRs make it difficult to actively modulate THz waves owing to unalterable resonant characteristics. Although the methods of applying external electric and optical fields to change the electromagnetic characteristics of SRRs, and thus achieving active modulation have been reported, the complicated heterostructure fabrication and optical measuring systems have also bring certain difficulties in experiments.

Recently, a research group led by Prof. Jianquan Yao and Prof. Lanju Liang from College of Precision Instruments and Opto-Electronics Engineering, Tianjin University reported the results of active THz modulation by changing the concentration of organic liquids flowing in microfluidic integrated metamaterial devices. This work provides another perspective for THz modulators based on metamaterials, which is published on Photonics Research Vol. 7, Issue 12, 2019 (Zhang Zhang, Ju Gao, Maosheng Yang, Xin Yan, Yuying Lu, Liang Wu, Jining Li, Dequan Wei, Longhai Liu, Jianhua Xie, Lanju Liang, Jianquan Yao. Microfluidic integrated metamaterials for active terahertz photonics[J]. Photonics Research, 2019, 7(12): 12001400).

In this work, a depletion layer played by aqueous organic liquids flowing in a platform of microfluidic integrated metamaterials is experimentally used to actively modulate terahertz (THz) waves. The polar configuration of water molecules in depletion layer gives rise to a damping of THz waves. The parallel coupling of such damping effect induced by depletion layer with the resonant response by metamaterials leads to an excellent modulation depth approaching 90% in intensity and a great difference over 210° in phase shift. Joint time-frequency analysis performed by the continuous wavelet transforms reveals the consumed energy with varying water content, indicating a smaller moment of inertia related to a shortened relaxation time of the depletion layer. This work diametrically highlights the availability of water in THz devices, and provides a new alternative for active modulation of terahertz photonics.

Academician Yao and Professor Liang believe that the results of this work are of great significance in the new THz modulation devices. Due to the transplantable microfluidic integration, it is also compatible with other functional metamaterials. Based on this work, the future goals of Prof. Liang’s group are focused on exploring microfluidic integrated metamaterial modulators and sensors with more functions and better performance by improving the structural design of microfluidics and optimize metamaterial performance.


The active modulation of THz waves realized by microfluidic integrated metamaterials.