Recent advances of exceptional points (EP) based sensing applications: A review

Sensors are used for the detection of target signals, whose their working principle is based on a probe of degenerate resonant frequencies (or energy levels) separated, which the responses are typically linear proportional to signal strengths.However, target signals in most circumstances are weak, as a result, it is crucial to design highly sensitive sensors. Recently, significant progresses have been made in the development of exceptional point (EP)-based sensors with significantly enhanced sensitivity. The EP is originated from non-Hermitian systems, that possesses an unique feature of not only the corresponding eigenvalues degenerated but also the associated eigenvectors collapsed. As non-Hermitian systems operate near an EP, a faint external perturbation to systems would dramatically lift the degeneracy, leading to a strong spectra splitting behavior that can be quantitatively measured. As non-Hermitian systems with n-fold degenerate EP, i.e., there are n eigenvalues and eigenvectors coalesce, splitting spectra can be significantly detached that the enhancement can be up to n-th square root of an external perturbed strength, offering a promising pathway for high-sensitivity sensing. This article examines optical and electronic sensors leveraging EPs, exploring the mechanisms behind their superior sensitivity, the challenges they currently face, and their potential for future advancements