Harnessing Nonlinearity to Tame Wave Dynamics in Nonreciprocal Active Systems

Field transformation, as an extension of the transformation optics, provides a unique means for nonreciprocal wave manipulation, while the experimental realization remains a significant challenge as it requires stringent material parameters of the metamaterials, e.g., purely nonreciprocal bianisotropic parameters. Here, we develop and demonstrate a nonreciprocal field transformation in a 2D acoustic system, using an active metasurface that can independently control all consti...

Non-Hermitian skin effect (NHSE), indicating the breakdown of conventional bulk-boundary correspondence, is a most intriguing phenomenon of non-Hermitian systems. Previous realizations of NHSE typically require unequal left-right couplings or on-site gain and loss. Here we propose a new mechanism for realizing NHSE via dissipative couplings, in which the left-right couplings have equal strengths but the phases do not satisfy the complex conjugation. When combined with multi-c...

We propose a dynamically tunable nonreciprocal response for wave propagations by employing nonlinear Fano resonances. We demonstrate that transmission contrast of waves propagation in opposite directions can be controlled by excitation signal. In particular, the unidirectional transmission can be flipped at different times of a pulse, resembling a diode operation with {\em dynamical reconfigurable nonreciprocity}. The key mechanism is the interaction between the linear and no...

The motive of this work is to understand the complex spatial characteristics of finite-amplitude elastic wave propagation in periodic structures and leverage the unique opportunities offered by nonlinearity to activate complementary functionalities and design adaptive spatial wave manipulators. The underlying assumption is that the magnitude of wave propagation is small with respect to the length scale of the structure under consideration, albeit large enough to elicit the ef...

We report experimental results and study theoretically soliton formation and propagation in an airfilled acoustic waveguide side loaded with Helmholtz resonators. Our theoretical approach relies on a transmission-line description of this setting, which leads to a nonlinear dynamical lattice model. The latter is treated analytically, by means of dynamical systems and multiscale expansion techniques, and leads to various soliton solutions for the pressure. These include Boussin...

Space-time-varying materials pledge to deliver nonreciprocal dispersion in linear systems by inducing an artificial momentum bias. Although such a paradigm eliminates the need for actual motion of the medium, experimental realization of space-time structures with dynamically changing material properties has been elusive. In this letter, we present an elastic metamaterial that exploits stiffness variations in an array of geometrically phase-shifted resonators -- rather than ex...

Flexible mechanical metamaterials are compliant structures engineered to achieve unique properties via the large deformation of their components. While their static character has been studied extensively, the study of their dynamic properties is still at an early stage, especially in the nonlinear regime induced by their high deformability. Nevertheless, recent studies show that these systems provide new opportunities for the control of large amplitude elastic waves. Here, we...

We introduce a class of unidirectional lasing modes associated with the frozen mode regime of non-reciprocal slow-wave structures. Such asymmetric modes can only exist in cavities with broken time-reversal and space inversion symmetries. Their lasing frequency coincides with a spectral stationary inflection point of the underlying passive structure and is virtually independent of its size. These unidirectional lasers can be indispensable components of photonic integrated circ...

The nonlinear Fourier transform (NFT), a powerful tool in soliton theory and exactly solvable models, is a method for solving integrable partial differential equations governing wave propagation in certain nonlinear media. The NFT decorrelates signal degrees-of-freedom in such models, in much the same way that the Fourier transform does for linear systems. In this three-part series of papers, this observation is exploited for data transmission over integrable channels such as...

We demonstrate that the temporal reflection of a weak dispersive pulse on a soliton in media with a frequency-dependent nonlinearity leads to the generation of new solitons, whose number can be selected by tuning parameters of the dispersive pulse. By carefully analyzing the different processes involved, we show that a virtuous interplay between Raman scattering and a zero-nonlinearity wavelength is a key enabler for soliton generation to occur, limiting the initial soliton r...