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Wang Z, Pan WK, He Y et al. Efficient generation of vectorial terahertz beams using surface-wave excited metasurfaces. Opto-Electron Sci 4, 240024 (2025). doi: 10.29026/oes.2025.240024
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Efficient generation of vectorial terahertz beams using surface-wave excited metasurfaces
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Abstract
On-chip devices for generating pre-designed vectorial optical fields (VOFs) under surface wave (SW) excitations are highly desired in integrated photonics. However, conventional devices are usually of large footprints, low efficiencies, and limited wave-control capabilities. Here, we present a generic approach to design ultra-compact on-chip devices that can efficiently generate pre-designed VOFs under SW excitations, and experimentally verify the concept in terahertz (THz) regime. We first describe how to design SW-excitation metasurfaces for generating circularly polarized complex beams, and experimentally demonstrate two meta-devices to realize directional emission and focusing of THz waves with opposite circular polarizations, respectively. We then establish a systematic approach to construct an integrated device via merging two carefully designed metasurfaces, which, under SW excitations, can separately produce pre-designed far-field patterns with different circular polarizations and generate target VOF based on their interference. As a proof of concept, we demonstrate experimentally a meta-device that can generate a radially polarized Bessel beam under SW excitation at ~0.4 THz. Experimental results agree well with full-wave simulations, collectively verifying the performance of our device. Our study paves the road to realizing highly integrated on-chip functional THz devices, which may find many applications in biological sensing, communications, displays, image multiplexing, and beyond.-
Keywords:
- surface waves /
- vector beam /
- multi-pixel metasurface /
- terahertz /
- ultrathin and high-efficiency
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References
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Wang Z, Pan WK, He Y et al. Efficient generation of vectorial terahertz beams using surface-wave excited metasurfaces. Opto-Electron Sci 4, 240024 (2025). doi: 10.29026/oes.2025.240024
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Figure 1.
Schematic illustrations of working mechanism and vectorial light field generation by the proposed SW MS. (a, b) Schematics of mulitiple mode generation by a PB MS illuminated by linearly polarized free-space light with different incident angles. (c) Schematic of single mode radiation with the specific spin state by a PB MS illuminated by SW. (d) Schematic of the complex vectorial light field radiation created by a multi-pixel MS capable of decoupling both LCP and RCP components with well-controlled phase difference, under excitation of impinging SWs.
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Figure 2.
Design and characterization of the PB meta-atom and plasmonic metal. (a) The sample image of the proposed metal-insulator-metal typed meta-atoms arranged in a periodic array with the geometry shown in the inset. Here, p = 166.6 μm, L = 132 μm, W = 23.5 μm, and d = 60 μm. (b) The reflection amplitudes |ruu|, |rvv| and phase difference Δφ =φuu − φvv of the meta-atoms illuminated by the terahertz light linearly polarized along the two principle axes, i.e., u and v axes, obtained by both simulations and experiments. (c) The retrieved efficiency of normal and abnormal reflection modes (Rn and Ra) based on the data in (b). (d) Simulated dispersion relation of eigen SW modes supported by the designed plasmonic metal.
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Figure 3.
Near-field mapping and far-field angle-resolved characterization of SW-PW unidirectional radiation. (a, b) Schematic illustration and sample picture of the on-chip metadevice with the MS and plasmonic metal jointed together to achieve unidirectional spin-polarized far-field radiation of SWs. (c, e) Measured and simulated electric field Re(Ey) distributions on the xz plane of the MS excited by the near-field SWs launched along −x direction at 0.4 THz. (d, f) Scattered electric field intensity (color map) carrying LCP and RCP of the MS at different radiation angles and frequencies.
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Figure 4.
Characterization of far-field focusing of SW with the proposed on-chip meta-device. (a) Schematic of the SW-PW focusing with pre-defined spin state by the MS carrying specific geometric phase distribution. (b) Top-view picture of part of the fabricated MS sample. Measured (c, d), and simulated (e, f) electric field Re(Ex) distributions on the xz plane (y=0 mm) plane and the xy plane (z=2 mm) plane of the sample excited by SWs at 0.4 THz. In this case, all the fields are normalized to the corresponding maximum values in the patterns.
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Figure 5.
Vectorial Bessel beam generation with the on-chip THz multi-pixel MS. (a) Schematic of the design flowchart of the SW MS for creating complex vectorial FF. (b) Schematic of the conversion from SW to radially polarized Bessel FF beam. Part of the sample picture is shown as the inset in this figure. (c, d) Measured and simulated electric field |Ex|2 intensity distribution on the xz plane (y=0 mm) when plane-wave like SWs at 0.4 THz enter the MS. (e−h) Measured electric field intensity distribution projected to the different linear polarization states of the generated vectorial Bessel beam on xy plane (z=2 mm) at 0.4 THz.
