Passively Tunable Terahertz Filters Using Liquid Crystal Cells Coated with Metamaterials

Chiang, Wei-Fan, Yu-Yun Lu, Yin-Pei Chen, Xin-Yu Lin, Tsong-Shin Lim, Jih-Hsin Liu, Chia-Rong Lee, and Chia-Yi Huang. "Passively tunable terahertz filters using liquid crystal cells coated with metamaterials." Coatings 11, no. 4 (2021): 381.

for full paper see https://www.mdpi.com/2079-6412/11/4/381/pdf

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Abstract

Liquid crystal (LC) cells that are coated with metamaterials are fabricated in this work. The LC directors in the cells are aligned by rubbed polyimide layers, and make angles θ of 0◦ , 45◦ , and 90◦ with respect to the gaps of the split-ring resonators (SRRs) of the metamaterials. Experimental results display that the resonance frequencies of the metamaterials in these cells increase with an increase in θ, and the cells have a maximum frequency shifting region of 18 GHz. Simulated results reveal that the increase in the resonance frequencies arises from the birefringence of the LC, and the LC has a birefringence of 0.15 in the terahertz region. The resonance frequencies of the metamaterials are shifted by the rubbing directions of the polyimide layers, so the LC cells coated with the metamaterials are passively tunable terahertz filters. The passively tunable terahertz filters exhibit promising applications on terahertz communication, terahertz sensing, and terahertz imaging.


Experimental

.......Figure 2 displays the experimental terahertz spectra of three metamaterials that are coated with the PI layers. These spectra are obtained using a commercial terahertz spectrometer (TPS 3000, TeraView, Cambridge, UK) in transmission mode, and the chamber in the spectrometer is filled with nitrogen gas to prevent terahertz waves from absorbing moisture. The polarization of incident terahertz waves is set parallel to the x axis of Figure 1a. The PI-coated metamaterials have transmission peaks in their terahertz spectra due to the absorption of the electromagnetic resonance of the metamaterials. The transmission peaks are at an identical frequency of 0.588 THz, and the two PI-coated metamaterials .........

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