Coherent perfect absorber and laser modes in purely imaginary metamaterials

Abstract

Conjugate metamaterials, in which the permittivity and the permeability are complex conjugates of each other, possess the elements of loss and gain simultaneously. By employing a conjugate metamaterial with a purely imaginary form, we propose a mechanism for realizing both coherent perfect absorber (CPA) and laser modes, which have been widely investigated in parity-time symmetric systems. Moreover, the general conditions for obtaining CPA and laser modes, including obtaining them simultaneously, are revealed by analyzing the wave scattering properties of a slab made of purely imaginary conjugate metamaterials. Specifically, in a purely imaginary conjugate metamaterial slab with a sub-unity effective refractive index, perfect absorption can be realized for the incident wave from air.

Coherent perfect absorption and laser modes in a cylindrical structure of conjugate metamaterials

“…L C a a p = = In this way, the studied CM becomes n i 1 C M e = and n i , 1 CM m =which is a special CMs, i.e., PIM [28,31]. To match the amplitude 1 m x = for CPA and laser modes, the following conditions should be met, i.e., V 1 m =for laser…”

“…Nevertheless, we can flexibly construct non-Hermitian metamaterials with gain or loss, hence with new interesting optical phenomena, such as gain-loss induced stable surface waves [24]. Recently conjugate metamaterials (CMs) x x * e m = ( ( ) ( )) [25], as a kind of non-Hermitian metamaterials [26], which involve optical loss and gain simultaneously but possess purely real refractive indexes [27], have been studied extensively [28][29][30][31]. Such media exhibit special optical features.…”

“…Moreover, based on CPA and laser modes in purely imaginary metamaterials (PIMs) [31], perfectly bidirectional negative refraction can be realized by utilizing such a pair of PIM slabs, which is a breakthrough to the unidirectional limit in PT symmetric systems. Therefore, these works [28][29][30][31] also provide alternative evidence that PT-symmetry is not necessary condition for achieving the coexistence of CPA and laser modes, which has been indicated in [32,33].…”

Negative refraction based on purely imaginary metamaterials

“…Before further discussions, let us revisit the CPA and laser effects in a PICM slab in air [26]. As shown in Fig.…”

“…Recently, as a kind of non-Hermitian materials, conjugate metamaterials (CMs) have drawn much attention [25][26][27][28]   , such CMs are purely imaginary; CPA and laser modes (even their coexistence) can be found in a slab of purely imaginary conjugate metamaterials (PICMs) [26]. Therefore, the PICMs might be used to achieve negative refraction, overcoming the disadvantages of both bulk metamaterials and PT symmetric systems.…”