Exceptional points (EPs) in non-Hermitian systems, where eigenvalues and eigenvectors coalesce, offer unique advantages in state transitions, non-reciprocal devices, and sensing, owing to their distinctive and extraordinary properties. Most prior studies for sensing at EPs focused on mode splitting, with limited focus on leveraging the linewidth broadening mechanism. In this study, we construct an EP by embedding two nanoholes within a microdisk cavity. With nanoparticle adsorption at the edge of the microcavity at the EP, the linewidth of two split modes exceeds the frequency splitting, enabling the use of the linewidth broadening mechanism for nanoparticle detection. By calculating the linewidth of the transmission spectra with or without the adsorption of the nanoparticle, an enhanced linewidth broadening based on the EP is achieved compared to that based on the diabolic point (DP). We observe that the linewidth broadening based on the EP varies periodically with the azimuthal position of the nanoparticle along the edge of the cavity. Specifically, the maximum of the linewidth broadening based on the EP is several times larger than that based on the diabolic point. This paper not only deepens our understanding of non-Hermitian physics in microcavities but also lays the groundwork for future research and applications in high-sensitivity sensing.

An exceptional nexus (EX), a higher-order exceptional point where multiple exceptional arcs converge, has garnered significant attention in various physical domains, such as hybrid topological invariants and asymmetric state transfer. Previous studies on the dynamics encircling EX have primarily concentrated on transitions between stable states. To explore the transition from stable to unstable state in a nonlinear system, we construct an EX by coupling a saturated gain and a linear lossy optical microcavity and modulate the evolution rate of this EX. When dynamically encircling this EX, the stable state transfers to an unstable state at an optimal evolution rate range, exhibiting an asymmetric state transfer dependent on the starting point. Increasing the system’s gain parameter or reducing the loss parameter broadens the optimal evolution rate range for the transition from the stable to the unstable. By altering the starting point and shape of the evolution trajectory, the optimal range for the evolution rate will adjust correspondingly. Our work elucidates the fundamental physics of encircling EX and provides an alternative approach for manipulating optical modes in nonlinear non-Hermitian systems, particularly regarding transitions to the unstable state.

Dynamical encircling exceptional point(EP) shows a number of intriguing physical phenomena and its potential applications. To enrich the manipulations of optical systems in experiment, here, we study the dynamical encircling EP, i.e. state transfer process, in largely detuned multimode optomechanical system. The process of state transfer has been investigated with different factors about the location of start point, the orientation and the initial state of the trajectories around the EP in parameter space. Results show that the nonreciprocal and the chiral topological energy transfer between two optical modes are performed successfully by tuning the effective optomechanical coupling in the multimode system with large detuning. Moreover, the factor of evolution speed about system parameters is also discussed. Our work demonstrates the fundamental physics around EP in large detuning domain of multimode optomechanical system and provides an alternative for manipulating of optical modes in non-hermitian system.

Non-Hermitian systems associated with exceptional points (EPs) are expected to demonstrate a giant response enhancement for various sensors. The widely investigated enhancement mechanism based on diverging from an EP should destroy the EP and further limits its applications for multiple sensing scenarios in a time sequence. To break the above limit, here, we proposed a new enhanced sensing mechanism based on shifting an EP. Different from the mechanism of diverging from an EP, our scheme is an EP nondemolition and the giant enhancement of response is acquired by a slight shift of the EP along the parameter axis induced by perturbation. The new sensing mechanism can promise the most effective response enhancement for all sensors in the case of multiple sensing in a time sequence. To verify our sensing mechanism, we construct a mass sensor and a gyroscope with concrete physical implementations. Our work will deepen the understanding of EP-based sensing and inspire designing various high-sensitivity sensors in different physical systems.

Whispering-gallery-mode (WGM) microcavities have shown significant applications in nanoparticle sensing for environmental monitoring and biological analysis. However, the enhancement of detection resolution often calls for active cavities or elaborate structural designs, leading to an increase of fabrication complexity and cost. Herein, heterodyne amplification is implemented in WGM microsensors based on backscattering detection mechanism. By interfering with an exotic reference laser, the reflecting light backscattered by perturbation targets can be strongly enlarged, yielding an easy-to-resolve and consequently sensitive microsensor. The dependence of detection laser frequency has also been characterized with the assistance of optothermal dynamics. We show that exploiting heterodyne interferometry boosts the detection of weak signals in microresonator systems and provides a fertile ground for optical microsensor development.

The polarization beam splitter (PBS) is a crucial photonic element to separately extract transverse-electric and transverse-magnetic polarizations from propagating light fields. Here, we propose a concise, continuously tunable, and all-optical partial PBS in a vector optomechanical system which contains two orthogonal polarized cavity modes with degenerate frequency. The results show that one can manipulate the polarization states of different output fields by tuning the polarization angle of the pumping field and the system functions as a partial PBS when the pump laser polarizes vertically or horizontally. As a significant application of the tunable PBS, we propose a scheme of implementing quantum walks in resonator arrays without the aid of other auxiliary systems. Furthermore, we investigate the optomechanically induced Faraday effect in a vector optomechanical system which enables arbitrary tailoring of the input lights and the behaviors of polarization angles of the output fields in the undercoupling, critical coupling, and overcoupling regimes. Our findings prove the optomechanical system is a potential platform to manipulate the polarization states in multimode resonators and boost the process of applications related to polarization modulation.

The ground state cooling of Brillouin scattering optomechanical system is limited by defects in practical sample. In this paper, we propose a new compensatory cooling mechanism for Brillouin scattering optomechanical system with exceptional points (EPs). By using the EPs both in optical and mechanical modes, the limited cooling process is compensated effectively. The dual-EPs system, which is discovered in this work for the first time, can be induced by two defects with specific relative angles and has function of not only actively manipulating the coupling strength of optical modes but also the Brillouin phonon modes. Our results provide new tools to manipulate the optomechanical interaction in multi-mode systems and open the possibility of quantum state transfer and quantum interface protocols based on phonon cooling in quantum applications.

We report a novel, to the best of our knowledge, way to achieve phase-controlled dual-wavelength resonance based on whispering-gallery-mode (WGM) microcavities experimentally. With the help of a feedback waveguide, not only two optical pathways but also a unidirectional coupling between counter-propagating waves are formed, which is the requirement of all-optical analogues of electromagnetically induced transparency and Autler-Townes splitting. By adjusting the accumulating phase introduced from the fiber waveguide, we observe the signal lineshape changes from symmetric to asymmetric, i.e., the resonant transmission and extinction ratio of two splitting modes can be controlled, which brings a new degree of freedom to the WGM resonator system. These results may boost the development of quantum state control and pave the way for reconfiguring devices such as narrow-band filters.

The photonic router is a key device in optical communication and quantum networks. Here, the results of a study of multi‐channel optical routing using optomechanical multimode interference in an optical microcavity are reported. The optomechanical system used here exhibits multi‐optical modes and a mechanical mode. Optomechanical induced transparency and absorption appear in the system due to the interference between different paths. It is shown that the system can be served as a three‐port routing in the red‐detuned region to rout photons from the input port to an arbitrarily selected output port with high routing efficiency by controlling the parameters corresponding to different interference paths.

In article number 2000506, Gui#x02010;Lu Long and co#x02010;workers report the results of a study of multi#x02010;channel optical routing using optomechanical multimode interference in an optical microcavity. They show three#x02010;port routing in the red#x02010;detuned region to rout photons from the input port to an arbitrarily selected output port with high routing efficiency with this system. This is achieved by controlling the parameters corresponding to different interference paths.

Exploring quantum technology to precisely measure physical quantities is a meaningful task for practical scientific researches. Here, we propose a novel quantum sensing model based on color detuning dynamics with dressed states driving (DSD) in stimulated Raman adiabatic passage. The model is valid for sensing different physical quantities, such as magnetic field, mass, rotation and so on. For different sensors, the used systems can range from macroscopic scale, e.g. optomechanical systems, to microscopic nanoscale, e.g. solid spin systems. The dynamics of color detuning of DSD passage indicates the sensitivity of sensors can be enhanced by tuning system with more adiabatic or accelerated processes in different color detuning regimes. To show application examples, we apply our approach to build optomechanical mass sensor and solid spin magnetometer with practical parameters.

The sensitivity of perturbation sensing can be effectively enhanced with higher-order exceptional points due to the nonlinear response to frequency splitting. However, experimental implementation is challenging since all the parameters need to be precisely prepared. The emergence of an exceptional surface (ES) improves the robustness of the system to the external environment, while maintaining the same sensitivity. Here, we propose, to our knowledge, the first scalable protocol for realizing a photonic high-order ES with passive resonators. By adding one or more additional passive resonators in the low-order ES photonic system, the three- or arbitrary N-order ES is constructed and proved to be easily realized in experiment. We show that the sensitivity is enhanced and the experimental demonstration is more resilient against fabrication errors. The additional phase-modulation effect is also investigated.

By preparing a sensor system around isolated exceptional points, one can obtain a great enhancement of the sensitivity benefiting from the non‐Hermiticity. However, this comes at the cost of reduction of the flexibility of the system, which is critical for practical applications. By generalizing the exceptional points to exceptional surfaces, it has been theoretically proposed recently that enhanced sensitivity and flexibility can be combined. Here, an exceptional surface is experimentally demonstrated in a non‐Hermitian photonic sensing system, which is composed of a whispering‐gallery‐mode microresonator and two nanofiber waveguides, resulting in a unidirectional coupling between two degenerate counter‐propagating modes with an external optical isolator. The system is simple, robust, and can be easily operated around an exceptional surface. On the one hand, sensitivity enhancement is observed by monitoring the resonant frequency splitting caused by small perturbations. This demonstration of exceptional‐surface‐enhanced sensitivity paves the way for practical non‐Hermitian sensing applications. On the other hand, the suppression of frequency splitting around the exceptional surface is also shown for the first time.

Rare-earth-doped on-chip microlasers are of great significance in both fundamental research and engineering. To the best of our knowledge, this is the first report of Yb3+-doped and Er3+/Yb3+-codoped on-chip microsphere lasers fabricated via sol-gel synthesis. Laser emissions were observed in a band around 1040 nm in both Yb3+-doped and Er3+/Yb3+-codoped resonators pumped at 980 nm and had measured ultralow thresholds of 5.2 µW and 0.6 µW, respectively. Both single-mode and multi-mode emissions were recorded around 1040 nm in these lasers. Single-mode and two-mode emissions were obtained at 1550 nm in the Er3+/Yb3+-codoped lasers when pumped at 980 nm and 1460 nm, respectively. Furthermore, quality factors induced by different loss mechanisms in the microsphere lasers are theoretically estimated. These resonators are expected to contribute to the high-density integration of on-chip silica-based microlasers.

We theoretically study the optomechanically induced transparency (OMIT) and absorption(OMIA) phenomena in a single microcavity optomechanical system, assisted by an indirectly-coupledauxiliary cavity mode. We show that the interference effect between the two optical modes playsan important role and can be used to control the multiple-pathway induced destructive or construc-tive interference effect. The three-pathway interference could induce an absorption dip within thetransparent window in the red sideband driving regime, while we can switch back and forth betweenOMIT and OMIA with the four-pathway interference. The conversion between the transparencypeak and absorption dip can be achieved by tuning the relative amplitude and phase of the multiplelight paths interference. Our system proposes a new platform to realize multiple pathways inducedtransparency and absorption in a single microcavity and a feasible way for realizing all-opticalinformation processing.

High-sensitivity gyroscope is widely used for rotation detection in several practical applications. Recently, exceptional points (EPs) have garnered considerable attention for enhancing the sensitivity of sensors based on optical cavities. Here, we propose an EP-enhanced optical gyroscope based on mechanical parity-time (PT) symmetry in a microcavity system. We demonstrate that by pumping the two optical modes with different colors, i.e., blue and red detuning, an effective mechanical PT-symmetric system can be obtained, and the system can be prepared at EP with appropriate parameters. The sensitivity of gyroscope at EP was enhanced by more than one order of magnitude in the weak perturbation regime as compared to that at diabolic point. This indicates that the sensitivity of gyroscope can be effectively enhanced by monitoring the mechanical modes rather than the optical modes. Overall, our work provides a promising approach to design high-sensitivity gyroscopes in optical microcavities and is potentially useful in a variety of research fields including fundamental physics and precision measurement.

Fabricating an optical microtoroid with ultra-high quality factor is an indispensable procedure both for scientific research and engineering. Here, HF/HNO3 wet etching is specially tailored to form silicon pillars for ultra-high quality factor microtoroids instead of xenon difluoride (XeF2) or reactive ion etching (RIE) methods. This is a low-cost, easily maintained and time-saving method. The method uses a very simple etching device and is robust to temperature variations and humidity changes at room temperature(20-25 degrees C). Anisotropy in isotropic HF/HNO3 etching, which may limit the quality factor, is minimized in the experiment. Quality factor dependence on silicon orientation is experimentally investigated and theoretically explained with group theory, which shows that [111] oriented silicon wafers are superior to [100] and [110] in the wet etching method. The maximum quality factor observed at 1550 nm waveband in the experiment is 1.05 x 10(8). We believe this technique will have great influence both on laboratory and future production use.

As an important device for detecting rotation, high sensitivity gyroscope is required for practical applications. In recent years, exceptional point (EP) shows its potential in enhancing the sensitivity of sensing in optical cavity. Here we propose an EP enhanced optical gyroscope based on mechanical PT-symmetric system in microcavity. By pumping the two optical modes with different colors, i.e. blue and red detuning, an effective mechanical PT-symmetric system can be obtained and the system can be prepared in EP with appropriate parameters. Compared with the situation of diabolic point, EP can enhance the sensitivity of gyroscope with more than one order of magnitude in the weak perturbation regime. The results show the gyroscope can be enhanced effectively by monitoring mechanical modes rather than optical modes. Our work provides a promising approach to design gyroscope with higher sensitivity in optical microcavity and has potential values in some fields including fundamental physic and precision measurement.

Optical nonreciprocity and routing using optocal microcavities draw much atttention in recent years. Here, we report the results of the study on the nonreciprocity and routing using optomechanical multimode interference in an optical microcavity. The optomechanical system used here possesses multi-optical modes and a mechanical mode. Optomechanical induced transparency and absorption, appear in the system due to the interference between different paths. The system can present significant nonreciprocity and routing properties when appropriate parameters of the system are set. We design quantum devices, such as diode, circulator and router, which are important applications. Our work shows that optomechanical multimode system can be used as a promising platform for buliding photonic and quantum network.