(INVITED) Exceptional points of parity-time- and anti-parity-time-symmetric devices for refractive index and absorption-based sensing

Parity-time symmetry has gained attention in optical research, for the interesting properties of exceptional points of showing enhanced sensitivity to external perturbation. Such a property has been widely proposed for different applications. Recently, also anti-parity-time symmetry has gained a growing interest and has been proposed as an alternative to parity-time-symmetric sensors. However, in literature, the effect of the eigenfrequency splitting on the measurable transfer function in the proximity of exceptional point is often neglected, leading to unstable systems and complex readout schemes. In this work it will be shown how parity-time-symmetric and anti-parity-time-symmetric high-sensitivity sensors can be properly designed for refractive index and absorption-based sensing, guaranteeing stability and simplicity of the readout scheme.