Acoustic Topological Fano Resonances

Originally discovered in the context of quantum mechanics in 1961, the ultra-sharp spectrum of the Fano resonance has nowadays established itself as centerpiece in modern engineering for realizing a large variety of prominent devices including low energy switches [1], efficient sources and emitters [2], and highly sensitive interferometers [3]. In addition, the peculiar asymmetric line shape of the Fano resonance is found to be substantially sensitive to environmental changes, establishing a unique platform for the implementation of highly sensitive sensors and actuators [4]. The excessive sensitivity of the Fano resonance to environmental and structural parameters is, however, not always desirable as it makes the practical implementation of Fano structures extremely challenging, mitigating the performance advantages obtained from Fano interference by costs related to the fabrication technology. Here, we report our recent theoretical findings and experimental observations of acoustic topological Fano resonances whose much-sought line-shapes is guaranteed by topology, offering a unique protection against geometrical tolerances. We construct such topological Fano resonances from interaction between a bright and a dark mode that both have topological origin, and demonstrate this concept experimentally for audible airborne sound in a one-dimensional acoustic scenario. By going beyond the performance degradation caused by inadvertent fabrication flaws, such protection paves the way for a new generation of Fano-based acoustic devices which, not only possess exotic properties as any other Fano structure, but also can be readily implemented in practice with very low cost [5]. 1. K. Nozaki, et al. Optics express 21.10 (2013): 11877-11888. 2. S. Chua, et al. Optics express 19.2 (2011): 1539-1562. 3. K. Heeg, et al. Physical review letters 114.20 (2015): 207401. 4. C. Wu, et al. Nature materials 11.1 (2012): 69. 5. F. Zangeneh-Nejad, and R. Fleury, Physical review letters. 122 (2019): 01430