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[Editors Pick] Current Optics and Photonics Vol. 3 no. 4 (2019 August)

한국광학회 hit 842 date 2021-04-05

Chirality in Non-Hermitian Photonics

Sunkyu Yu, Xianji Piao, and Namkyoo Park*

Photonic Systems Laboratory, Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Korea

 

 

 

Current Optics and Photonics  Vol. 3 No. 4 (2019 August) pp. 275-284
DOI: https://doi.org/10.3807/COPP.2019.3.4.275

 


 


Fig. 1  Chirality in different physical domains of nonHermitian photonics. For the optical field, E = eA(r,R)exp (iωt - ik(R) · rr), where R is the system parameter vector and r is the position vector, the extended definition of optical chirality in non-Hermitian photonics can be classified according to each physical quantity: polarization e for SAM, wavefrontA(r,R) for OAM, canonical momentum k(R) for wave propagation, and the geometry of state evolution in the system parameter space R. The system parameter R represents the complex optical potential that determines the condition of PT symmetry, including on-site and hopping constants defined by structural and material parameters.

 

 

Abstract

Chirality is ubiquitous in physics and biology from microscopic to macroscopic phenomena, such as fermionic interactions and DNA duplication. In photonics, chirality has traditionally represented differentiated optical responses for right and left circular polarizations. This definition of optical chirality in the polarization domain includes handedness-dependent phase velocities or optical absorption inside chiral media, which enable polarimetry for measuring the material concentration and circular dichroism spectroscopy for sensing biological or chemical enantiomers. Recently, the emerging field of non-Hermitian photonics, which explores exotic phenomena in gain or loss media, has provided a new viewpoint on chirality in photonics that is not restricted to the traditional polarization domain but is extended to other physical quantities such as the orbital angular momentum, propagation direction, and system parameter space. Here, we introduce recent milestones in chiral light-matter interactions in non-Hermitian photonics and show an enhanced degree of design freedom in photonic devices for spin and orbital angular momenta, directionality, and asymmetric modal conversion.