$\mathcal{PT}$-symmetric microring laser-absorber

TL;DR

This paper theoretically investigates $ ext{PT}$-symmetric microring lasers with gratings, revealing conditions for unidirectional lasing and coherent perfect absorption, including mode control and symmetry-breaking effects.

Contribution

It introduces a theoretical analysis of $ ext{PT}$-symmetric microring lasers, highlighting new regimes for unidirectional lasing and CPA at symmetry-breaking points.

Findings

Perfect unidirectional laser emission at the symmetry-breaking point.

Simultaneous lasing and CPA achievable above the symmetry-breaking point.

Controllable excitation of clockwise and counterclockwise modes.

Abstract

The lasing and coherent perfect absorption (CPA) properties of $\mathcal{PT}$-symmetric microrings with mixed index and gain gratings, externally coupled to a bus waveguide, are theoretically investigated. For a complex grating at the $\mathcal{PT}$ symmetry breaking point, perfect unidirectional (either clockwise or counterclockwise) laser emission can be realized, however the grating does not discriminate longitudinal modes and CPA can not be simultaneously achieved. Above the grating $\mathcal{PT}$ symmetry breaking point, single mode emission and simultaneous CPA can be obtained, with unbalanced and controllable excitation of clockwise and counterclockwise modes in the ring.