Non-reciprocal photonics based on time modulation

Sounas, Dimitrios L.; Alù, Andrea

doi:10.1038/s41566-017-0051-x

Cited by 788 publications

(470 citation statements)

References 68 publications

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“…Reciprocity. Reciprocity implies that if a signal can travel down a certain path, the same signal should be able to travel back with the same transmission strength [36][37][38][39][40][41]. If the system is reciprocal, the scattering operator is symmetric: ˆT SS = .…”

Section: S-matrix Symmetry Propertiesmentioning

confidence: 99%

Anomalies in light scattering

et al. 2019

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Scattering of electromagnetic waves lies at the heart of most experimental techniques over nearly the entire electromagnetic spectrum, ranging from radio waves to optics and X-rays. Hence, deep insight into the basics of scattering theory and understanding the peculiar features of electromagnetic scattering is necessary for the correct interpretation of experimental data and an understanding of the underlying physics. Recently, a broad spectrum of exotic scattering phenomena attainable in suitably engineered structures has been predicted and demonstrated.Examples include bound states in the continuum, exceptional points in -symmetrical non-Hermitian systems, coherent perfect absorption, virtual perfect absorption, nontrivial lasing, nonradiating sources and cloaking, and others. In this paper, we establish a unified description of such exotic scattering phenomena and show that the origin of all these effects can be traced back to the properties of the underlying scattering matrix. two or three dimensions. Maxwell's equations describing spatial and temporal evolution of electric ( , ) t Er and magnetic ( , ) t Hr fields for an arbitrary system are

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Section: S-matrix Symmetry Propertiesmentioning

confidence: 99%

Anomalies in light scattering

et al. 2019

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“…In this section, we look at one of the highly applauded features of space-time gradient metasurfaces which is the magnetless nonreciprocal response [34,[36][37][38][39][40][41][42][43][44][45] and explore the utility of modulation-induced phase shift in obtaining a strong nonreciprocal response and isolation via spatial decomposition of frequency harmonics. The origin of nonreciprocity in space-time gradient metasurfaces is the difference in the imparted momentum by the metasurface to the forward and backward propagating waves.…”

Section: Nonreciprocal Response and Isolationmentioning

confidence: 99%

“…Introducing time-modulation in a structure leads to generation of higher-order frequency harmonics and breaks the time-reversal symmetry [32][33][34][35]. A significant effort has been devoted into developing magnetless nonreciprocal devices by adopting a periodic spatiotemporal modulation along the propagation direction which mimics a traveling wave motion and enables isolation and circulation of light by imparting different momentums to forward and backward propagating waves [36][37][38][39][40][41][42][43][44][45]. Moreover, timemodulated metasurfaces hold a great potential to extend the degree of light manipulation.…”

Section: Introductionmentioning

confidence: 99%

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

2018

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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 timemodulated metasurface which is linearly proportional to 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, with the highest efficiency occurring in the vicinity of resonance, and decreasing away from the resonant regime. The modulation-induced phase shift allows for creating tunable spatially varying phase discontinuities with 2π span in the wavefronts of generated frequency harmonics for a wide range of frequencies and incident angles. Specifically, we apply this approach to a time-modulated metasurface in the Teraherz 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 with large isolations via modulationinduced 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.

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“…The electromagnetic Lorentz reciprocity theorem [1][2][3][4] states that in a linear, timeindependent system with symmetric constitutive optical tensors, the ratio between received and transmitted fields are the same for forward and time-reversed propagation directions. While most electromagnetic and photonic devices operate under this principle, there are circumstances in which reciprocity has undesirable effects, e.g., photovoltaic cells re-emitting absorbed solar energy or antennas listening to their own echo.…”

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confidence: 99%

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

et al. 2020

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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.

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Non-reciprocal photonics based on time modulation

Cited by 788 publications

References 68 publications

Anomalies in light scattering

Anomalies in light scattering

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

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

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