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Register a new userFree Control of Far-Field Scattering Angle of Transmission Terahertz Wave using Multilayer Split-Ring Resonators Metasurfaces
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To enhance transmission efficiency of Pancharatnam-Berry (PB) phase metasurfaces, multilayer split-ring resonators were proposed to develop encoding sequences. As per the generalized Snell law, the deflection angle of the PB phase encoding metasurfaces depends on the metasurface period size. Therefore, it is impossible to design an infinitesimal metasurface unit.Consequently, the continuous transmission scattering angle cannot be obtained. In digital signal processing, this study introduces the Fourier convolution principle on encoding metasurface sequences to freely control the transmitted scattering angles. Both addition and subtraction operations between two different encoding sequences were then performed to achieve the continuous variation of the scattering angle. Furthermore, we established that the Fourier convolution principle can be applied to the checkerboard coded metasurfaces.
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Multilayer metasurfaces (MLMs) represent a versatile type of three-dimensional optical metamaterials that could enable ultra-thin and multi-functional photonic components. Herein we demonstrate an approach to readily fabricate MLMs exploiting a thin film self-rolling technique. As opposed to standard layer-by-layer approaches, all the metasurfaces are defined within a single nanopatterning step, significantly reducing fabrication time and costs. We realize two MLMs platforms relying on widely used nanopatterning techniques, namely focused ion-beam and electron-beam lithographies. A first example are MLMs comprised of nanohole patterns structured into metal-dielectric seed bilayers. The second platform is comprised of vertical stacks of angled plasmonic nanorod arrays separated by thin dielectric layers. Such angled MLMs exhibit a selective response to circularly polarized light, in agreement with previous works relying on layer-by-layer processes. Our approach can pave the way for the efficient prototyping of novel MLMs, such as devices with varying number of layers and configurations that can be fabricated on a single chip.
Excitation of antiferromagnetic spin waves in HoFeO$_{3}$ crystal combined with a split ring resonator (SRR) is studied using terahertz (THz) electromagnetic pulses. The magnetic field in the vicinity of the SRR induced by the incident THz electric field component excites and the Faraday rotation of the polarization of a near-infrared probe pulse directly measures oscillations that correspond to the antiferromagnetic spin resonance mode. The good agreement of the temperature-dependent magnetization dynamics with the calculation using the two-lattice Landau-Lifshitz-Gilbert equation confirms that the spin wave is resonantly excited by the THz magnetic near-field enhanced at the LC resonance frequency of the SRR, which is 20 times stronger than the incident magnetic field.
Lithography-free metasurfaces composed of a nano-layered stack of materials are attractive not only due to their optical properties but also by virtue of fabrication simplicity and cost reduction of devices based on such structures. We demonstrate a multi-layer metasurface with engineered electromagnetic absorption in the mid-infrared (MIR) wavelength range. Characterisation of thin SiO$_2$ and Si films sandwiched between two Au layers by way of experimental absorption and thermal radiation measurements as well as finite difference time domain (FDTD) numerical simulations is presented. Comparison of experimental and simulation data of optical properties of multilayer metasurfaces show guidelines for the absorber/emitter applications.
We introduce the concept of controlling the nonlinear response of the metamaterial by altering its internal structure. We experimentally demonstrate tuning of the nonlinear response of two coupled split-ring resonators by changing their mutual position. This effect is achieved through modification of the structure of the coupled resonant modes, and their interaction with the incident field. By offsetting the resonators we control the maximum currents through the nonlinear driving elements, which affects the nonlinear response of the system.
The Terahertz or millimeter wave frequency band (300 GHz - 3 THz) is spectrally located between microwaves and infrared light and has attracted significant interest for applications in broadband wireless communications, space-borne radiometers for Earth remote sensing, astrophysics, and imaging. In particular optically generated THz waves are of high interest for low-noise signal generation. In particular optically generated THz waves are of high interest for low-noise signal generation. Here, we propose and demonstrate stabilized terahertz wave generation using a microresonator-based frequency comb (microcomb). A unitravelling-carrier photodiode (UTC-PD) converts low-noise optical soliton pulses from the microcomb to a terahertz wave at the solitons repetition rate (331 GHz). With a free-running microcomb, the Allan deviation of the Terahertz signal is 4.5*10^-9 at 1 s measurement time with a phase noise of -72 dBc/Hz (-118 dBc/Hz) at 10 kHz (10 MHz) offset frequency. By locking the repetition rate to an in-house hydrogen maser, in-loop fractional frequency stabilities of 9.6*10^-15 and 1.9*10^-17 are obtained at averaging times of 1 s and 2000 s respectively, limited by the maser reference signal. Moreover, the terahertz signal is successfully used to perform a proof-of-principle demonstration of terahertz imaging of peanuts. Combining the monolithically integrated UTC-PD with an on-chip microcomb, the demonstrated technique could provide a route towards highly stable continuous terahertz wave generation in chip-scale packages for out-of-the-lab applications. In particular, such systems would be useful as compact tools for high-capacity wireless communication, spectroscopy, imaging, remote sensing, and astrophysical applications.
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