Multifaceted anapole: from physics to applications [Invited]

The optical anapole state resulting from interference of the electric and toroidal moments is of much interest due to its nonradiating nature. Interference of optical modes supported by a diverse range of Mie-resonant structures has found many applications, such as in biosensors and optical communication. This review provides an overview of the recent progress of anapole states in photonics. After a brief historical background, a complete mathematical description is presented. It allows one to clearly demonstrate and identify the existence of anapole states and highlight their fundamental properties. Then, we focus on the excitation of anapoles in photonics and discuss the relation to other states, such as bound states in the continuum. Finally, we discuss a series of advances that uncover the anapole potential in various applications, from nonlinear photonics and lasing to optical communication and sensing.