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Tunable terahertz fishnet metamaterials based on thin nematic liquid crystal layers for fast switching.

Zografopoulos DC, Beccherelli R - Sci Rep (2015)

Bottom Line: A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values.Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components.Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

View Article: PubMed Central - PubMed

Affiliation: Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi (CNR-IMM), Roma 00133, Italy.

ABSTRACT
The electrically tunable properties of liquid-crystal fishnet metamaterials are theoretically investigated in the terahertz spectrum. A nematic liquid crystal layer is introduced between two fishnet metallic structures, forming a voltage-controlled metamaterial cavity. Tuning of the nematic molecular orientation is shown to shift the magnetic resonance frequency of the metamaterial and its overall electromagnetic response. A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values. Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components. Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

No MeSH data available.


Spatial profile of the three components of the electric field for the non-resonant frequency f0 = 0.95 THz and the two resonant frequencies fH = 1.05 THz and fL = 0.87 THz, which correspond to the LC molecules aligned along the x− and z−axis, respectively.The fishnet dimensions are W = 110 μm and w = 40 μm.
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f3: Spatial profile of the three components of the electric field for the non-resonant frequency f0 = 0.95 THz and the two resonant frequencies fH = 1.05 THz and fL = 0.87 THz, which correspond to the LC molecules aligned along the x− and z−axis, respectively.The fishnet dimensions are W = 110 μm and w = 40 μm.

Mentions: Figure 2 shows the transmittance, reflectance, and absorption spectra of the fishnet LC-THz-MM, for W = 110 μm and w = 40 μm, calculated for both limiting cases and asssuming x− or y−polarization for a perpendicularly impinging plane wave. It is remarked that for the lattice constant here considered, the cutoff frequency for the lowest non-zero diffraction order in the polymer substrate is above the spectral window under investigation34. Calculations were performed by means of the finite element method45, imposing periodic boundary conditions at the side-walls of the unit cell shown in Fig. 1. A broadband transmission window centered at approximately 0.95 THz can be observed for both polarization and LC orientations. This corresponds to the EM mode supported through the swiss-cross shaped apertures formed in-between the fishnet metallic structures. The corresponding field profiles calculated at the z = 0 plane, shown in Fig. 3, verify that at 0.95 THz the electric field is mainly confined in the apertures, resembling a TE10 mode, which is excited since the length of the swiss-cross is adequate to provide high transmittance (cf. the limit of Ly/2 in the case of a periodic array of subwavelength square holes46). Although the structure itself is symmetric, owing to the presence of the LC material, there is a degree of anisotropy in the EM response in the rest case, which is investigated in Fig. 2(a). On the contrary, in the fully switched case, the response is polarization-independent, as both polarizations of the plane wave sense the ordinary LC index.


Tunable terahertz fishnet metamaterials based on thin nematic liquid crystal layers for fast switching.

Zografopoulos DC, Beccherelli R - Sci Rep (2015)

Spatial profile of the three components of the electric field for the non-resonant frequency f0 = 0.95 THz and the two resonant frequencies fH = 1.05 THz and fL = 0.87 THz, which correspond to the LC molecules aligned along the x− and z−axis, respectively.The fishnet dimensions are W = 110 μm and w = 40 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4536660&req=5

f3: Spatial profile of the three components of the electric field for the non-resonant frequency f0 = 0.95 THz and the two resonant frequencies fH = 1.05 THz and fL = 0.87 THz, which correspond to the LC molecules aligned along the x− and z−axis, respectively.The fishnet dimensions are W = 110 μm and w = 40 μm.
Mentions: Figure 2 shows the transmittance, reflectance, and absorption spectra of the fishnet LC-THz-MM, for W = 110 μm and w = 40 μm, calculated for both limiting cases and asssuming x− or y−polarization for a perpendicularly impinging plane wave. It is remarked that for the lattice constant here considered, the cutoff frequency for the lowest non-zero diffraction order in the polymer substrate is above the spectral window under investigation34. Calculations were performed by means of the finite element method45, imposing periodic boundary conditions at the side-walls of the unit cell shown in Fig. 1. A broadband transmission window centered at approximately 0.95 THz can be observed for both polarization and LC orientations. This corresponds to the EM mode supported through the swiss-cross shaped apertures formed in-between the fishnet metallic structures. The corresponding field profiles calculated at the z = 0 plane, shown in Fig. 3, verify that at 0.95 THz the electric field is mainly confined in the apertures, resembling a TE10 mode, which is excited since the length of the swiss-cross is adequate to provide high transmittance (cf. the limit of Ly/2 in the case of a periodic array of subwavelength square holes46). Although the structure itself is symmetric, owing to the presence of the LC material, there is a degree of anisotropy in the EM response in the rest case, which is investigated in Fig. 2(a). On the contrary, in the fully switched case, the response is polarization-independent, as both polarizations of the plane wave sense the ordinary LC index.

Bottom Line: A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values.Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components.Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

View Article: PubMed Central - PubMed

Affiliation: Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi (CNR-IMM), Roma 00133, Italy.

ABSTRACT
The electrically tunable properties of liquid-crystal fishnet metamaterials are theoretically investigated in the terahertz spectrum. A nematic liquid crystal layer is introduced between two fishnet metallic structures, forming a voltage-controlled metamaterial cavity. Tuning of the nematic molecular orientation is shown to shift the magnetic resonance frequency of the metamaterial and its overall electromagnetic response. A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values. Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components. Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

No MeSH data available.