Abstract
Space−time modulated metamaterials support extraordinary rich applications, such as parametric amplification, frequency conversion, and non-reciprocal transmission. The non-Hermitian space−time varying systems combining non-Hermiticity and space−time varying capability, have been proposed to realize wave control like unidirectional amplification, while its experimental realization still remains a challenge. Here, based on metamaterials with software-defined impulse responses, we experimentally demonstrate non-Hermitian space−time varying metamaterials in which the material gain and loss can be dynamically controlled and balanced in the time domain instead of spatial domain, allowing us to suppress scattering at the incident frequency and to increase the efficiency of frequency conversion at the same time. An additional modulation phase delay between different meta-atoms results in unidirectional amplification in frequency conversion. The realization of non-Hermitian space−time varying metamaterials will offer further opportunities in studying non-Hermitian topological physics in dynamic and nonreciprocal systems.
Highlights
Space−time modulated metamaterials support extraordinary rich applications, such as parametric amplification, frequency conversion, and non-reciprocal transmission
Temporal modulation of material parameters has been applied on metamaterials to further extend the degrees of freedom in wave control[16,17,18,19,20,21,22,23,24,25,26,27,28,29,30], which opens further possibilities for extraordinary physics like tunable frequency conversion[18,19], non-reciprocal propagation[20,21,22,23,24,25,26,27,28,29], time reversal mirror[31,32], parametric amplification[33,34], and topological pumping[35,36,37]
It has been proposed to add non-Hermiticity into time-varying systems to achieve phenomena such as unidirectional amplification[42,43], bidirectional invisibility[34], tunable exceptional points by modulation[44], and nonreciprocal edge state propagating in non-Hermitian Floquet insulators[45]
Summary
Space−time modulated metamaterials support extraordinary rich applications, such as parametric amplification, frequency conversion, and non-reciprocal transmission. Based on metamaterials with software-defined impulse responses, we experimentally demonstrate non-Hermitian space −time varying metamaterials in which the material gain and loss can be dynamically controlled and balanced in the time domain instead of spatial domain, allowing us to suppress scattering at the incident frequency and to increase the efficiency of frequency conversion at the same time. Temporal modulation of material parameters has been applied on metamaterials to further extend the degrees of freedom in wave control[16,17,18,19,20,21,22,23,24,25,26,27,28,29,30], which opens further possibilities for extraordinary physics like tunable frequency conversion[18,19], non-reciprocal propagation[20,21,22,23,24,25,26,27,28,29], time reversal mirror[31,32], parametric amplification[33,34], and topological pumping[35,36,37]. Due to the flexibility of our software-defined metamaterial platform, we can arbitrarily define the “energy-level” diagrams to manipulate the frequency-converted modes, in analogy to quantum interference effect
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