Non-Hermitian Physics and Engineering in Silicon Photonics

Driven by the great needs for low-cost and scalable advanced optoelectronic systems that could leverage the existing infrastructure already developed for the semiconductor industry, silicon photonics has been extensively explored as a platform with system-level integration to host numerous devices and systems with various functionalities, including lasers, modulators, filters, isolators, wavelength division multiplexing (WDM) transceivers, etc. Recently, non-Hermitian physics, which breaks the conventional scope of quantum mechanics based on Hermitian Hamiltonians, has been widely explored in the platform of silicon photonics. With judicious designs of refractive index, modal coupling and gain–loss distribution, unconventional control and manipulation of light flow and nonlinear effects could be achieved. As we will discuss in this chapter, the unconventional properties of exceptional points and parity-time symmetry realized in silicon photonics have created new opportunities for ultrasensitive sensors, laser engineering, control of light propagation, topological mode conversion, etc. The marriage between the quantum non-Hermiticity and classical silicon platforms not only inspires numerous studies on the fundamental physics but also enriches the potential functionalities of the integrated photonic systems.