Nanoparticle Detection Based On Microcavity Exceptional Point Characteristics

Cavity optomechanics is a frontier subject that combines optical microcavities and the mechanical resonator to study the interaction between the cavity field and the mechanical resonator.In recent years,thanks to the great progress of micro-nano processing technology,the quality factor of optical microcavity has been continuously improved,and the volume of the mode has been continuously reduced.and the cavity photodynamics has been developed rapidly.It is widely used in ground-state cooling,basic physics,phonon lasing,and weak-force sensing.At the same time,the properties and applications of the exceptional point systems have attracted much attention in recent years,showing great development potential.The special physical mechanism of the exceptional point produces many novel physical effects such as chiral laser,slow-to-fast light switch,and non-reciprocal optical transmission.Among them,the feature that exceptional point can improve the measurement accuracy makes its application in optically sensitive detection attract wide attention.In this paper,we discuss two different situations in the cavity optical system.In the first first case,in the whispering gallery mode resonant microcavity coupled with three nanoparticles,by the optomechanically induced transparency at the exceptional point to detect the third particle.The expressions of the transmittance and group delay of the probe beam in the model are analytically solved,and the influence of the presence of the third particle on the transmission spectrum is discussed in detail.Our results show that the existence of the third particle can make the optomechanically induced transparency phenomenon more sensitive at the exceptional point.This provides a more sensitive method for adjusting the spread of light,and on the other hand,it can also be passed the output spectrum of the detection light is changed to identify the presence of the third particle,thereby realizing particle detection.In addition,we have also found that adjusting the relative position of the nanoparticles to make the system close to or far from the exceptional point can realize the slow-to-fast light switch of the detection light.Based on the first case,considering that the third particle has internal degrees of freedom,that is,in the resonant cavity of the whispering gallery mode coupling two nanoparticles and a two-level atom,study the influence of the coupling strength between the two-level atom and the cavity field on the transmission spectrum.Our results show that:through the change of the transmission spectrum,in turn,the detection of the coupling strength between the atom and the cavity field can be achieved,and we have proved that the system is in the sensitivity of detection can be enhanced near the exceptional point.It is worth mentioning that adjusting the coupling strength between the atom and the cavity field can also be used to manipulate the group delay and advance of the probe light.