Parity-time symmetry breaking optical nanocircuit

Abstract

Gain and loss balanced parity-time (PT) inversion symmetry has been achieved across multiple platforms including acoustics, electronics, and photonics. Tunable subwavelength asymmetric transmission based on PT symmetry breaking has attracted great interest. However, due to the diffraction limit, the geometric size of an optical PT symmetric system is much larger than the resonant wavelength, which limits the device miniaturization. Here, we theoretically studied a subwavelength optical PT symmetry breaking nanocircuit based on the similarity between a plasmonic system and an RLC circuit. Firstly, the asymmetric coupling of an input signal is observed by varying the coupling strength and gain-loss ratio between the nanocircuits. Furthermore, a subwavelength modulator is proposed by modulating the gain of the amplified nanocircuit. Notably, the modulation effect near the exceptional point is remarkable. Finally, we introduce a four-level atomic model modified by the Pauli exclusion principle to simulate the nonlinear dynamics of a PT symmetry broken laser. The asymmetric emission of a coherent laser is realized by full-wave simulation with a contrast of about 50. This subwavelength optical nanocircuit with broken PT symmetry is of great significance for realizing directional guided light, modulator and asymmetric-emission laser at subwavelength scales.

Nonlocal Metasurface with Chiral Exceptional Points in the Telecom-Band

“…When g = Γ, i.e., at EP, both the eigenvalues (ω ± = E 0 ) and the eigenstates ± x iy ( ) of the system degenerate as shown in the middle panel of Figure 1c (denoted by green star), indicating that an RCP beam transmits through the metasurface without any conversion to LCP. Different from EP formed without a polarization selection structure, 12,13 the EP formed by such a PT symmetric metasurface exhibits distinctive chiral characteristics in polarization space. To design the metasurface, the key parameters are the rod size and pitches along the x and y directions, both of which can affect the resonance and line width of meta-atoms.…”

“…Bender and Boettcher theoretically proved that a non-Hermitian system can also have real eigenvalues if PT symmetry is satisfied, i.e., [ H PT ] = 0. , In 2007, El-Ganainy and his colleagues used the mathematical equivalence between the single-particle Schrödinger equation and the paraxial approximate electromagnetic wave equation, replacing the complex potential function with the complex refractive index, i.e., n ( x ) = n *­(− x ), and introduced the PT symmetry to the optical field, where the gain can be implemented through gain materials and external source pumping. Therefore, photonic systems provide a fertile ground to investigate non-Hermitian Hamiltonians and PT symmetry, giving rise to many interesting phenomena, such as single-mode lasing, , non-reciprocal light transmission, − negative refraction, asymmetric optical response, − coherent perfect absorber, − PT -symmetry-induced bound state in the continuum, etc.…”