A Tunable Dispersion‐Free Terahertz Metadevice with Pancharatnam–Berry‐Phase‐Enabled Modulation and Polarization Control

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199

Metasurfaces, two‐dimensional versions of metamaterials, retain the great capabilities of three‐dimensional counterparts in manipulating electromagnetic wave behaviors, while reducing the challenges in fabrication. By judiciously engineering parameters of individual building blocks (such as geometry, size, and material) and selecting specific design algorithms, metasurfaces are promising to replace conventional electromagnetic elements in nanoplasmonic/photonic devices. Significantly, such concept can be readily promoted to other disciplines, such as acoustics, thermal physics, and seismology. In this article, the latest advances in full control of electromagnetic waves with metasurfaces are briefly reviewed from a functionality perspective. A broad avenue towards real‐life applications of metamaterials has been opened up, although they are still at their infant stage. At the end, several promising approaches are suggested to extend the applications of metasurfaces.

Section: Pancharatnam-berry Phasementioning

confidence: 99%

Advances in Full Control of Electromagnetic Waves with Metasurfaces

Zhang

Mei

Huang

et al. 2016

357

199

“…[ 22,23 ] Arbitrary manipulation of local and global polarization of output radiation has been a very important research hot spot that fi nds applications in holography, [24][25][26] beam splitter, [ 27 ] vector beam generation, [ 28 ] and polarization control. [29][30][31][32][33][34][35] In this work, we provide a new perspective of near-fi eld coupling where we demonstrate a passive switching of the near-fi eld inductive coupling induced excitation in orthogonally twisted meta-atoms where the coupling channel is switched on in one confi guration (MM1, See Figure 1) and switched off in another confi guration (MM2) without any change in the geometrical distance between the near-fi eld coupled meta-atoms. The electromagnetic nearfi eld coupling between the meta-atom induces the crosspolarized radiation that is switched on and off as the coupling channel is switched on and off, which plays a dominant role in determining the output polarization state of light.…”

mentioning

confidence: 99%

Near‐Field Inductive Coupling Induced Polarization Control in Metasurfaces

Cong

Srivastava

Singh

2016

Self Cite

wileyonlinelibrary.com COMMUNICATIONAs shown in Figure 1 , we fabricated several planar metamolecular arrays that consist of two orthogonal SRRs in each unit cell on a double-polished high resistivity silicon. The fabrication was performed using conventional photolithography, development, metallization, and lift-off processes (See the Experimental Section for details). All the SRRs are identical in size that are made up of aluminum and the geometrical parameters are shown in Figure 1 . The left and right SRRs in the meta-molecular unit cell are designated as SRR1 and SRR2, respectively. SRR1 and SRR2 are orthogonally twisted and the distance between them in the unit cell is constant at d = 3 µm to ensure that two SRRs are well within the near-fi eld coupling distance. [ 21 ] The SRR2 in MM1 and MM2 are rotated clockwise and anticlockwise, respectively by 90° relative to SRR1 in order to obtain the polarization dependent excitation of meta-atoms in the meta-molecule.In order to measure the response of MM1 and MM2, we employed an 8-f antenna-based terahertz time-domain spectroscopy (THz-TDS) system [ 36 ] with a set of polarizers inserted in the measurement system to coherently measure the co-and crosspolarized transmission signals (See the Experimental Section for detail). [ 29 ] We obtained the time-domain waveforms and then converted them into frequency domain spectra with both amplitude and phase information using Fourier transform. The transmission amplitude spectra | ( )| t ji ω and the phase informa- ω is the complex transmitted reference signal, respectively. Here, the reference is an identical blank silicon substrate, and i and j represent the input and output polarization states. All the measurements were performed at normal incidence in dry nitrogen atmosphere. As shown in Figure 2 a,b, we exhibit the copolarized transmission spectra with x -polarized and y -polarized incidence, respectively. While comparing the response of MM1 and MM2 in Figure 2 a with x -polarized excitation where SRR1 is the directly excited meta-atom, a nonintuitive phenomenon occurs where MM1 and MM2 reveal disparate behaviors in the copolarized spectra. The mode interference spectrum of MM1 is commonly known due to the inductive coupling between SRR1 and SRR2 where the directly excited bright SRR1 induces the resonance in the unexcited SRR2 through a magnetic dipole that is defi ned as indirectly excited dark meta-atom. Surprisingly, we do not observe any spectral splitting in MM2 which indicates the absence of inductive coupling between SRR1 and SRR2. A similar orientation dependent coupling behavior is also revealed in Figure 2 b with y -polarized incidence where SRR2 is directly excited. The spectra with x -polarized and y -polarized incidence reveal the different response that originates from the anisotropy due to Metamaterials provide a distinct platform to manipulate the electromagnetic properties of artifi cially designed media for active and passive device functionalities, such as cloaking, [ 1 ] sensing, [ 2 ] perfect abs...

“…Recently, THz planar photonics are presented based on the wavefront manipulation arising from particularly designed subwavelength resonator units, i.e., metasurfaces . By this means, the amplitude, phase, and polarization of THz wave can be freely tailored . However, the high Ohmic loss of plasmonic metasurface results in a significantly suppressed efficiency.…”

Section: Introductionmentioning

confidence: 99%

Planar Terahertz Photonics Mediated by Liquid Crystal Polymers

Shen

Tang

Chen

et al. 2020

Terahertz (THz) band is expected to satisfy the ever‐increasing demand for high‐capacity wireless data transfer. Multifunctional photonic devices with compactness and low loss are highly pursued for future THz communications. Here, a strategy for planar THz photonics is proposed that enables free wavefront manipulation with submillimeter thin liquid crystal polymer (LCP) films. Such elements work on the spatial geometric phase modulation, which is accomplished by preprogramming the axis orientations of LCP. The LCP monomers follow the guidance of local photoalignment agent and are further polymerized under UV exposure at the existence of a doped photo‐initializer. Thanks to the high resolution and excellent flexibility of the photopatterning technique, THz elements with versatile functions can be realized. As examples, waveplates, polarization gratings, and lenses, which are suitable for the polarization control, beam deflecting, focusing, or collimating, are demonstrated. Due to the intrinsic flexibility of LCP films, an f‐tunable lens enabled by mechanically induced deformation is exhibited. Specific mode generators for vortices and Bessel beams are also presented, which can function as separate channels for the mode division multiplexing in THz communications. This work provides a robust platform for fabricating integrated, low‐loss, and tunable THz elements suitable for the advanced THz apparatuses.