Chiral Waveguides for Robust Waveguiding at the Deep Subwavelength Scale

Routing electromagnetic energy at a scale smaller than the wavelength is a highly sought functionality in a variety of applications, including compact lightweight satellite communications, slow-waves sensors, all-optical information processing, and energy harvesting. Unfortunately, strong field confinement at this scale requires the use of coupled subwavelength resonators, implying a large sensitivity to geometrical imperfections and disorder-induced backscattering. We propose a very unconventional solution to this problem by exploiting the interface modes occurring at the boundary between two chiral metamaterials composed of resonant metamolecules with opposite chirality. Our numerical and experimental results demonstrate the inherent robustness of these interface states to disorder in both the position and resonance frequency of the metamaterial’s meta-atoms. By computing transmission averages over many realizations of disorder, we quantitatively demonstrate the superiority of this form of subwavelength routing over previously proposed designs, including frequency-defect lines, symmetry-based topological edge modes, and Valley-Hall interface states.

Chiral Metamaterials for a Robust Waveguiding Scheme

Romain Christophe Rémy Fleury, Nadège Sihame Kaïna, Bakhtiyar Orazbayev

Recent advances in the field of metamaterials have shown that waves can be efficiently manipulated at the subwavelength scale through the interactions with an ensemble of resonant inclusions, opening new horizons in overcoming the size limits of devices which are often tied to the wavelength of operation [1]. Such size limit is crucial for many applications where the overall dimensions are required to be as small as possible, for instance cost-eﬃcient devices for satellite communications. Unfortunately, the resonant inclusions of these artificial media result in a large sensitivity of the propagation to geometrical imperfections and disorder-induced backscattering, reducing their performance. More recently, it has been demonstrated that the topological concepts which originated in solid-state physics can be transferred to not only to photonic crystals [3,4], which still scale with the operating wavelength, but also to locally-resonant crystalline metamaterials, which can have a deeply subwavelength structure [5]. However, since the topological properties in such time-reversal invariant designs heavily rely on the lattice structure of the media and frequency dispersion of the metamaterial, they are inevitably sensitive to any disruption of the lattice symmetries that can couple time-reversed modes. Moreover, since most of disorders (in the location or in resonance frequency of the resonant inclusions) will most likely break the lattice symmetry and disrupt the wave propagation, these time-reversal invariant topological designs are also in principle sensitive to defects. In this talk, we will show that a chiral metamaterial [6,7] can be exploited to create a robust-to-disorder subwavelength waveguide and we will demonstrate this possibility experimentally in the microwave regime. Moreover, we will quantitatively demonstrate the superior robustness of the proposed design to both spatial or frequency disorders by performing ensemble averages on disorder realizations along the path of the guided wave, and comparing them with previously proposed subwavelength waveguide designs: frequency defect lines, symmetry-based topological edge modes and valley interface states. [1] J. D. Joannopoulos, S. G. Johnson, J. N. Winn, and R. D. Meade, Photonic Crystals: Molding the Flow of Light (Princeton University Press, Princeton, 2008), 2nd ed. [2] N. Kaina, F. Lemoult, M. Fink, and G. Lerosey, Negative Refractive Index and Acoustic Superlens from Multiple Scattering in Single Negative Metamaterials, Nature, 525, 77 (2015). [3] S. Raghu and F. D. M. Haldane, Analogs of Quantum-Hall-Effect Edge States in Photonic Crystals, Phys. Rev. A - At. Mol. Opt. Phys., 78, 1 (2008). [4] Z. Wang, Y. Chong, J. D. Joannopoulos, and M. Soljacić, Observation of Unidirectional Backscattering-Immune Topological Electromagnetic States., Nature, 461, 772 (2009). [5] S. Yves, R. Fleury, T. Berthelot, M. Fink, F. Lemoult, and G. Lerosey, Crystalline Metamaterials for Topological Properties at Subwavelength Scales, Nat. Commun., 8, 16023 (2017). [6] M. Goryachev and M. E. Tobar, Reconfigurable Microwave Photonic Topological Insulator, Phys. Rev. Appl., 6, 1 (2016). [7] J. E. Vázquez-Lozano and A. Martínez, Optical Chirality in Dispersive and Lossy Media, Phys. Rev. Lett., 121, 43901 (2018).

2019

Subwavelength robust waveguiding with chiral metamaterial waveguides

Romain Christophe Rémy Fleury, Nadège Sihame Kaïna, Bakhtiyar Orazbayev

In this work, we design and experimentally demonstrate in the microwave range a robust metamaterial waveguide, which is formed at the boundary between two locally resonant chiral metamaterials with opposite chirality. We show that the interface states at such boundary are inherently robust to disorder in both the position and resonance frequency of subwavelength resonators. Moreover, we quantitatively demonstrate the superiority of the proposed subwavelength waveguiding over previously proposed designs, including frequency-defect lines, symmetry-based topological edge modes, and Valley-Hall interface states.

2019

Subwavelength robust waveguiding with chiral metamaterial waveguides

Romain Christophe Rémy Fleury, Nadège Sihame Kaïna, Bakhtiyar Orazbayev

IEEE2019

Chiral Metamaterials for a Robust Waveguiding Scheme

Romain Christophe Rémy Fleury, Nadège Sihame Kaïna, Bakhtiyar Orazbayev

2019