Manipulating the critical gain level of spectral singularity in active hybridized metamaterials.

In this paper, we investigate the spectral singularity in an active hybridized metamaterial, which manifests itself as ultra-high transmission and reflection at the same frequency in the far-field. A transmission line combined with lumped element model is utilized to describe the proposed active metamaterial. With this model, we reveal that the critical gain level for triggering the spectral singularity is related to the coupling strength between different components of the system. Through optimizing the coupling coefficients between different components, we demonstrate the spectral singularity of the proposed structure at very low gain level, which can bring active metamaterials systems a step closer to their practical implementation. Furthermore, we demonstrate rapid switching between two spectral singularities at different frequencies in the same structure by adding or reducing small amount of gain. The exotic properties of the proposed sub-wavelength structure promise applications in switching, sensing, spaser and nonlinear optics areas.