Abstract
An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with respect to the gaps of the split-ring resonators (SRRs) of the metasurface under various polarized directions of the pump beam. Experimental results display that the resonance frequency of the metasurface in the cell increases with an increase in θ, and the cell has a frequency tuning region of 15 GHz. Simulated results reveal that the increase in the resonance frequency arises from the birefringence of the LC, and the LC has a birefringence of 0.13 in the terahertz region. The resonance frequency of the metasurface is shifted using the pump beam, so the metasurface-imbedded LC cell with the photoalignment layers is an optically tunable terahertz filter. The optically tunable terahertz filter is promising for applications in terahertz telecommunication, biosensing and terahertz imaging.
Highlights
Photoalignment has attracted much attention due to its controllability on the orientations of liquid crystals (LCs) [1,2,3,4,5,6]
The terahertz metasurface that is imbedded into the LC cell with the photoalignment layers is an optically tunable terahertz filter and has potential in terahertz imaging, biosensing and terahertz telecommunication
The silver metasurface is oxidized in ambient environment, it is imbedded into the LC cell
Summary
Photoalignment has attracted much attention due to its controllability on the orientations of liquid crystals (LCs) [1,2,3,4,5,6]. The methyl red molecules in a dye-doped LC cell sequentially undergo absorption, photoisomerization, diffusion, desorption and adsorption on the irradiated surface of the cell after the cell is irradiated with a linearly polarized green light. Tunable terahertz filters based on metasurfaces that are imbedded into LC cells have not yet been developed, and exhibit many advantages such as free electrode-patterning, ease addressability and high potential for remote control in various ambient environments. The irradiation of a pump light with various polarized directions on the photoalignment layers causes the director reorientation, tuning the resonance frequency of the terahertz metasurface by a frequency tuning range of 15 GHz. A simulation reveals that the tuning of the resonance frequency is caused by the birefringence of the LC, and the LC has a birefringence of 0.13 in the terahertz region. The terahertz metasurface that is imbedded into the LC cell with the photoalignment layers is an optically tunable terahertz filter and has potential in terahertz imaging, biosensing and terahertz telecommunication
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