Quasibound states in the continuum induced by PT symmetry breaking

CPA-lasing associated with the quasibound states in the continuum in asymmetric non-Hermitian structures

“…To be consistent with Ref. [57], we take the permittivity of the loss and gain media ε ± (ω) = 1 ± iγ − ω 2 p /ω 2 , where ω p is the plasma frequency and γ is the non-Hermiticity magnitude. Exploitation of the classical Drude-Lorentz model does not spoil the conclusions we make further.…”

“…The loss layer has the thickness d + = λ p /2π (i.e., ω p d + /c = 1, where c is the speed of light), whereas the gain layer has different thickness d − = αd + , where α is the geometric asymmetry parameter. The parameters of the spacer are d il = 10d + and ε il = 5. In our previous paper [57], the symmetric case (α = 1) has been already studied. In the Hermitian limit (γ = 0), the symmetric system possesses an unobservable infinitely narrow resonance (BIC) due to destructive interference of the Fabry-Perot mode and the volume plasmon excited by TMpolarized waves at the plasma frequency.…”

“…In this paper, we study a non-Hermitian generalization of the ENZ-containing layered structures supporting bound states in the continuum. It has been recently shown [57] that PT -symmetry breaking in the structures with balanced loss and gain results in transformation of a BIC into quasi-BIC, which is the resonance with the finite Q factor. Here, we make a further step introducing asymmetry in the distribution of loss and gain.…”

“…(n is the integer), shows up in spectra as a finite-width resonance, see the solid line in Let us fix the angle of incidence (θ = θ BIC ≈ 23.881 • at n = 7) and the non-Hermiticity magnitude (γ = 0.001) and start changing the geometric asymmetry parameter α. Reflection spectra calculated within the transfer-matrix method [57] are shown in Fig. 2.…”

Synthesizing quasi-bound states in the continuum in epsilon-near-zero layered materials

“…Among the possible extensions, currently under way, it is worth mentioning the incorporation of gain constituents in order to balance the loss effects, along the lines of previous studies on parity-time symmetric configurations. 20,[26][27][28] Within this framework, also of great interest is the study of cylindrical geometries, 29,30 also taking into account the recent non-Hermitian extension of the photonic-doping concept. 31…”