Surface-wave-assisted nonreciprocity in spatio-temporally modulated metasurfaces

Abstract

Corresponding authors: A.A.: aazad@lanl.gov and D.D.: dalvit@lanl.gov 2 Emerging photonic functionalities are mostly governed by the fundamental principle of Lorentz reciprocity. Lifting the constraints imposed by this principle could circumvent deleterious effects that limit the performance of photonic systems. A variety of approaches have recently been explored to break reciprocity, yet most efforts have been limited to confined photonic systems. Here, we propose and experimentally demonstrate a spatiotemporally modulated metasurface capable of extreme breakdown of Lorentz reciprocity. Through tailoring the momentum and frequency harmonic contents of the scattered waves, we achieve dynamical beam steering, reconfigurable focusing, and giant free-space optical isolation exemplifying the flexibility of our platform. We develop a generalized Bloch-Floquet theory which offers physical insights into the demonstrated extreme nonreciprocity, and its predictions are in excellent agreement with experiments. Our work opens exciting opportunities in applications where free-space nonreciprocal wave propagation is desired, including wireless communications and radiative energy transfer.

Smart Doppler Cloak Operating in Broad Band and Full Polarizations

“…Recently, time-modulated metasurfaces have been verified that can be used to control dynamically the spectrum distribution of EM waves. [23][24][25][26][27][28][29][30] In particular, when the modulation waveform enables continuously linear variation of the reflection phase of metasurface in one modulation period T m , the incident frequency f i will be converted efficiently to a new frequency component f r upon reflection, and thus create a frequency shift Δf t = f r -f i (f r is the frequency of reflected waves). Under this modulation, the linearly varying reflection phase ϕ(t) of the metasurface is described as…”

Recent advances and perspectives on space-time coding digital metasurfaces

“…One of the most interesting and promising applications of space-time metastructures is the possibility to break Lorentz reciprocity without the need of magnetic or nonlinear materials. Theoretical [41][42][43] and experimental [44][45][46] studies have shown the possibility to attain nonreciprocal reflection or transmission effects via a metasurface imparting a suitable space-time phase gradient. In a recent study [30], this concept was implemented and demonstrated by relying on a space-time coding digital metasurface.…”

Full-duplex Reflective Beamsteering Metasurface Featuring Magnetless Nonreciprocal Amplification

“…Magnet-free nonreciprocal metasurfaces provide huge degrees of freedom for arbitrary alteration of the wavevector and temporal frequency of electromagnetic waves 8,12,[14][15][16][17][18][19][20][21][22][23][23][24][25] . They may be classified into two main categories, that is, space-time metasurfaces 12,17,19,21,21,23,[25][26][27][28][29] and transistor-loaded metasurfaces 8,15,[30][31][32][32][33][34] . Among these nonreciprocity approaches, transistorbased nonreciprocity is of high interest thanks to its immense capability for efficient nonreciprocal electromagnetic-wave amplification while breaking the time reversal symmetry.…”