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Helical Magnetic Field-Induced Real-Time Plasmonic Chirality Modulation
摘要： Astrophysical phenomenon mimetic helical magnetic field (hB)-assisted self-assembly is herein introduced to build helical superstructures that display chiroptical properties. As a building block, magnetoplasmonic (MagPlas) Ag@Fe3O4 core-shell nanoparticles are used to guide plasmonic Ag nanoparticles onto a helical magnetic flux. The chirality of the assembled helical structures and tailored circular dichroism are successfully tuned in real-time, and the handedness of the assembled structures is dynamically switched by the hB at the millisecond level, which is at least 6,000-fold faster than other template-assisted methods. The peak position of circular dichroism can be reconfigured by altering the plasmonic resonance or coupling by controlling the size of the Ag core and magnetic flux density. The hB-induced chirality modulation represents a method to control the polarization state of light at the nexus of plasmonics, magnetic self-assembly, colloidal science, liquid crystals, and chirality. It presents active and dynamic chiral assemblies of magnetoplasmonic nanomaterials, enabling further practical applications in optical devices.
关键词： magnetoplasmonic nanoparticles,helical magnetic field (hB),self-assembly,dynamic chirality,real-time modulation
更新于2025-09-23 15:19:57
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Time-modulated Conducting Oxide Metasurfaces for Adaptive Multiple Access Optical Communication
摘要： We demonstrate realization of a time-modulated metasurface in near-infrared frequency regime via integration of conducting oxide layers into plasmonic stripe nanoantennas arranged in a reflectarray configuration. The permittivity of conducting oxide layers is modulated in time through modulation of carrier concentration by applying radio-frequency biasing signals which leads to generation of higher-order frequency harmonics. We rigorously characterize the electro-optical frequency conversion performance of the metasurface. We then exploit the dispersionless angle-independent phase discontinuities on the wavefront of higher-order frequency harmonics to achieve dynamic multi-wavelength multi-beam scanning across S, C, and L telecommunication bands via pixelated control over the modulation phase delay. It is established that such time-modulated metasurfaces can be utilized as reflectarray antennas for active multicasting as well as wavelength and angle multiplexing, thus improving optical communication capacity by providing multiple access and integrating several communication channels into a single antenna platform. The role of modulation waveform in the spectral diversity of harmonics is also explored. Specifically, modulation waveform is optimized to realize unicast and broadcast links. Finally, active beam-scanning performance of the time-modulated conducting oxide metasurface is compared with that of its quasi-static counterpart verifying the enhanced bandwidth as well as suppressed side lobes in the time-modulated platform.
关键词： Metasurfaces,Time-Modulation,MIMO,Multiplexing,Multicasting,Transparent Conducting Oxides
更新于2025-09-11 14:15:04
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Beamforming Optimization for Time-Modulated Circular-Aperture Grid Array with DE Algorithm
摘要： This paper put forward a method of numerical optimization for the circular-aperture time-modulated grid array. The amplitude weight and time modulation pulse width are optimized based on differential evolution algorithm to get the needed array pattern. Adopting the weighting mode of conventional rectangular array, the equivalent weighting of circular-aperture time-modulated array is decomposed into two independent components respectively in horizontal and vertical direction, so to shorten the length of optimization vector from M×N order to M+N order. Besides, the circular-aperture time-modulated array is symmetrically excited in horizontal and vertical direction. The numerical experiments show that differential evolution algorithm can realize sidelobe level of -35dB and nulling level of -60dB in the patterns of the center frequency and one chosen sideband, and the unexploited sidebands are also suppressed with their peak level lower than -35dB. Meanwhile the dynamic range of the amplitude weighting and time modulation pulse width can be limited in 10dB. The overall efficiency of the time-modulated array is 0.28.
关键词： Beamforming optimization,differential evolution algorithm,circular-aperture grid array,time modulation
更新于2025-09-10 09:29:36
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Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering
摘要： Modulation of metasurfaces in time gives rise to several exotic space-time scattering phenomena by breaking the reciprocity constraint and generation of higher-order frequency harmonics. We introduce a new design paradigm for time-modulated metasurfaces, enabling tunable engineering of the generated frequency harmonics and their emerging wavefronts by electrically controlling the phase delay in modulation. It is demonstrated that the light acquires a dispersionless phase shift regardless of incident angle and polarization, upon undergoing frequency conversion in a time-modulated metasurface which is determined by the modulation phase delay and the order of generated frequency harmonic. The conversion efficiency to the frequency harmonics is independent of modulation phase delay and only depends on the modulation depth and resonant characteristics of the metasurface element, with the highest efficiency occurring in the vicinity of resonance, and decreasing away from the resonance. The modulation-induced phase shift allows for creating tunable spatially varying phase discontinuities with 2π span at the generated frequency harmonics for a wide range of frequencies and incident angles. Specifically, we apply this approach to a time-modulated metasurface in the Terahertz regime consisted of graphene-wrapped silicon microwires. For this purpose, we use an accurate and efficient semi-analytical framework based on multipole scattering. We demonstrate the utility of the design rule for tunable beam steering and focusing of generated frequency harmonics, giving rise to several intriguing effects such as spatial decomposition of harmonics, anomalous bending with full coverage of angles and dual-polarity lensing. Furthermore, we investigate the angular and spectral performance of the time-modulated metasurface in manipulation of generated frequency harmonics to verify its constant phase response versus incident wavelength and angle. The nonreciprocal response of the metasurface in wavefront engineering is also studied by establishing nonreciprocal links via modulation-induced phase shift. The proposed design approach enables a new class of high-efficiency tunable metasurfaces with wide angular and frequency bandwidth, wavefront engineering capabilities, nonreciprocal response and multi-functionality.
关键词： Terahertz,wavefront engineering,nonreciprocal response,graphene,time-modulation,metasurfaces
更新于2025-09-09 09:28:46