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Nonreciprocity of the counterpropagating waves in a ring resonator induced by the rotation rate results in a measurable frequency shift. A self-reference measurement using mode broadening induced by backscattering is proposed to detect the rotation rate in a whispering gallery mode resonator with a cavity-made slot filled with atomic vapor. Through detuning an optical pump rate and a strong driving field coupled to a three-level atomic vapor, the backscattering generated by the cavity-made slot becomes sensitive to the rotation. Degenerate clockwise and counterclockwise modes couple to each other and create two new eigenmodes via manipulating the backscattering of the cavity-made slot. Detecting the mode broadening induced by the rotation rate enables the gyroscope’s sensitivity to be enhanced at least four orders of magnitude in a low Q factor microresonator.

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Detecting the size of a single nanoparticle with high precision is crucial to understanding the characteristic of the nanoparticle. Traditionally, a nanoparticle as a perturbation enters the mode volume of a cavity, leading to eigenfrequency splitting that is proportional to the perturbation strength. Here, we demonstrate the single particle detection based on the anti-parity-time (anti-PT) symmetric indirectly coupled whispering-gallery mode (WGM) cavities, which can be tailored to operate at exceptional points (EPs) where the two eigenvalues and the corresponding eigenstates coalesce. Due to the complex-square-root topology characteristic at the EPs, the frequency splitting exhibits a square-root dependence on the small perturbation. When operating the system at such an EP, the anti-PT symmetric WGM nanoparticle sensor exhibits giant enhancement (≈3 orders) in frequency splitting compared with a traditional single WGM sensor with the same perturbation. With respect to the PT symmetric nanoparticle sensor, our research exhibits a real eigenfrequency splitting, which can be directly detected.

The present paper theoretically demonstrates tunable Goos-Hänchen (GH) shift and beam splitting of the polarized light reflected from the cavity containing the double ladder energy level system. Simultaneously opposite GH shifts for left-circularly polarized (LCP) and right-circularly polarized (RCP) beams can be achieved under asymmetric field conditions. By adjusting the intensity (Rabi frequency) of probe or drive field, the GH shifts of LCP and RCP probe beams are manipulated at the same time. We also discuss the effects of probe field frequency detuning on GH shifts and identify the parameters region to obtain a large separate distance (∼320 μm) between LCP and RCP probe beams.