Photonic Spin Hall Effect In A Parity-time Symmetric Cavity And Its Sensing Application

When a linearly polarized beam impinges on an interface,the left-and right-handed circularly polarized components split perpendicular to the plane of incidence.This phenomenon is photonic spin Hall effect(SHE),which can be regarded as the optical version of electronic SHE.Photonic SHE provides a new platform to manipulate photons,and exhibits a unique potential for applications in spin-controlled photonic devices and precision metrology.However,photonic SHE is a tiny phenomenon,and the corresponding spin shift is in the subwavelength scale.Until now,many methods(such as surface plasmon resonance,Brewster angle,and the introduction of twodimension materials)have been proposed to enhance the photonic SHE.Very recently,the photonic SHE in a typical parity-time(PT)symmetric system with balanced gain and loss is enhanced near the exceptional point(EP)and coherent perfect absorption(CPA)-laser mode.Therefore,further studies of photonic SHE in this PT-symmetric system is highly desirable.Based on the above consideration,we investigated the photonic SHE of reflected and transmitted light in PT symmetric cavity,and then designed a refractive index sensor based on this photonic SHE.Some creative work and correspinding results are summarized as following:1.By inserting an air gap between two epsilon-near-zero dielectric slabs of balanced gain and loss,the PT symmetric cavity is established.Here,the scattering behaviors,including reflection and transmission,as well as the photonic SHE in the PT symmetric cavity are investigated.This cavity is found to exhibit a multiple PT symmetry characterized by alternating symmetric and broken phases.This multiple PT symmetry allows the photonic SHE of transmitted light to be easily manipulated in the ranges of broad angles.Near the resonance angle of CPA-laser mode,the enhanced photonic SHE of both transmitted and reflected light can reach its upper limitation(i.e.half of the beam waist),which are much larger than that of the PT-symmetric structure without air gap.2.A novel sensing scheme based on the photonic SHE enhanced by the excitation of CPA-laser mode in this PT-symmetric cavity is proposed.The results show that this refractive index sensor has a superior intensity sensitivity of 8762um/RIU,which outperforms the photonic SHE sensors enhanced by surface plasmon resonance.These findings provide an effective method to enhance the photonic SHE and therefore open the opportunity for developing the optical sensors based on the photonic SHE.