Effective PT-symmetric metasurfaces for subwavelength amplified sensing

Abstract

We propose a novel design principle for ultrathin metasurfaces to realize optically amplified sensing with a performance that exceeds those of passive coherent perfect absorbers by several orders of magnitude. Our strategy is based on a generalized condition of lasing, coherent perfect absorption and their coexistence in metamaterials that feature an effective PT-symmetry. The devices we introduce here can be operated in configurations that involve both a one-sided or a two-sided wave incidence, where the latter case allows us to tune the degree of amplified absorption through the coherent phase between the two input beams. We also discuss how the conditions on the material parameters can be relaxed, away from the ideal case, such that a substantial amplification of the sensing performance can easily be reached in practical applications.

Coherent perfect absorber and laser modes in purely imaginary metamaterials

“…In addition, the general conditions for realizing CPA and laser modes have been derived. We also identify the conditions for realizing CPA mode and laser mode simultaneously, with the case of normal incidence [22][23][24] as a special case. More interestingly, as a simplification of CPA modes, single-sided PA modes can be obtained in a PICM slab with a sub-unity effective index for the incident angle beyond the critical angle.…”

“…We acknowledge that PICMs are very hard to realize in practice as loss and gain parameters are included in the same medium. However, recently two schemes [23,24] to realize materials with properties similar to PICMs have been proposed. By employing PT-symmetric materials in layered structures [23], PICMs can be effectively mimicked, with the similar CPA-laser effect realized.…”

“…However, recently two schemes [23,24] to realize materials with properties similar to PICMs have been proposed. By employing PT-symmetric materials in layered structures [23], PICMs can be effectively mimicked, with the similar CPA-laser effect realized. The other method is that, based on the effective medium theory [25], PICMs could be well designed by using a photonic crystal composed of core-shell rods [24], in which loss and gain media are distributed in either the cores or the shells.…”

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

“…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].…”