Optical isolation based on space-time engineered asymmetric photonic band gaps

Chamanara, Nima; Taravati, Sajjad; Deck-Léger, Zoé-Lise; Caloz, Christophe

doi:10.1103/physrevb.96.155409

Cited by 120 publications

(85 citation statements)

References 66 publications

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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%

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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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Section: Nonreciprocal Response and Isolationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

2018

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“…Thus, when a wave incident on the structure is modulated at a frequency falling within these band gaps, complex and hence evanescent modes will be excited. In contrast to reciprocal media, STM media provide oblique ST photonic transitions and exhibit asymmetric band gaps [11], [45]. Fig.…”

Section: Applications Of St Modulationmentioning

confidence: 99%

Space-Time Modulation: Principles and Applications

2020

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The ever-increasing demand for high data rate wireless systems has led to a crowded electromagnetic spectrum. This demand has successively spurred the development of versatile microwave and millimeter-wave integrated components possessing high selectivity, multi-functionalities and enhanced efficiency. These components require a class of nonreciprocal structures endowed with extra functionalities, e.g., frequency generation, wave amplification and full-duplex communication. Space-time (ST) modulation has been shown to be a perfect candidate for high data transmission given its extraordinary capability for electromagnetic wave engineering. Spacetime-modulated (STM) media are dynamic and directional electromagnetic structures whose constitutive parameters vary in both space and time. Recently, STM media have received substantial attention in the scientific and engineering communities. The unique and exotic properties of STM media have led to the development of original physics concepts, and novel devices in acoustics, microwave, terahertz and optic areas. STM media were initially studied in the context of traveling wave parametric amplifiers in the 50s and 60s [1]- [6]. In that era, magnet-based nonreciprocity was the dominant approach to the realization of isolators, circulators and other nonreciprocal systems. However, magnet-based nonreciprocity is plagued with bulkiness, nonintegrability, heaviness and incompatibility with high frequency techniques.Recently, ST modulation has experienced a surge in scientific attention thanks to its extraordinary and unique nonreciprocity. It eliminates issues of conventional nonreciprocity techniques, such as bulkiness, heaviness and incompatibility with integrated circuit technology associated with magnetbased nonreciprocity, power restrictions of nonlinear-based nonreciprocity, and frequency limitations and low power handling of transistor-based nonreciprocity. It provides asymmetric interband photonic transitions [7]-[14], subluminal and superluminal phase velocities, and asymmetric dispersion diagrams [4], [11], [13], [14], and holds potential for energy accumulation [15]. Various enhanced-efficiency magnet-free microwave and optical components have been recently realized by taking advantage of the unique properties of ST modulation, including isolators [9], [11], [16]-[19], circulators [20]-[23],

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“…It is important to notice that, according to this definition, there is no frequency conversion between ports. Wave isolation realized with space-time modulated media has been demonstrated in a few papers [29,31,35,47], where the classical scattering matrix [see Eq. (20)] is not suitable to describe those systems.…”

Section: A Metasurface Isolatorsmentioning

confidence: 99%

Theory and Design of Multifunctional Space-Time Metasurfaces

et al. 2020

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Integrating multiple functionalities into a single metasurface is becoming of great interest for future intelligent communication systems. While such devices have been extensively explored for reciprocal functionalities, in this work, we integrate a wide variety of nonreciprocal applications into a single platform. The proposed structure is based on spatiotemporally modulated impedance sheets supported by a grounded dielectric substrate. We show that, by engineering the excitation of evanescent modes, nonreciprocal interactions with impinging waves can be configured at will. We demonstrate a plethora of nonreciprocal components such as wave isolators, phase shifters, and circulators, on the same metasurface. This platform allows switching between different functionalities only by modifying the pumping signals (harmonic or non-harmonic), without changing the main body of the metasurface structure. This solution opens the door for future real-time reconfigurable and environment-adaptive nonreciprocal wave controllers.

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Optical isolation based on space-time engineered asymmetric photonic band gaps

Cited by 120 publications

References 66 publications

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

Space-Time Modulation: Principles and Applications

Theory and Design of Multifunctional Space-Time Metasurfaces

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