Guest Editorial Introduction to the Issue on Parity Time Photonics

The 17 papers in this special issue focus on parity time photonics, a new field of modern applied physics and design engineering. The enabling concept of parity time symmetry has garnered attention, in particular in the fields of optics, photonics and the design of new materials as well forward looking photonic integrated circuits. This is a result of applying such concepts for the design of photonic devices that has opened up many new technology paths and device functionalities. Examples include Bragg gratings with unidirectional invisibility, single mode nano-lasers based on parity time symmetry breaking and super-sensitive sensors, even new acoustic phononic devices. Equally important, non-Hermitian photonic structures that deviate from the exact Parity Time symmetry can also exhibit novel behavior such as pump-controlled random lasing, a loss-induced lasing onset and constant intensity waves in a non-uniform scattering landscape. The objective of this issue is to highlight recent progress and trends in this field.