Experimental Realization of Sensitivity Enhancement and Suppression with Exceptional Surfaces

Abstract

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.

Linear response theory of open systems with exceptional points

“…The first step can be straightforward in simple systems. b In systems that exhibit exceptional hypersurfaces in the parameter space 23 , 104 , 125 – 127 , finding such a perturbation can be a very complex task since any perturbation that shifts the system along the surface will fail. In addition, taking the limit when ϵ → 0 involves the cancellation of several singular terms with opposite signs.…”

Anomalous spontaneous emission dynamics at chiral exceptional points

“…Exceptional points (EPs), the spectral degeneracies where two or more eigenvalues and the associated eigenstates simultaneously coalesce, are the central concept in non-Hermitian physics [1][2][3][4][5]. A plethora of intriguing effects and exotic phenomena emerge around EPs due to their nontrivial topological properties and the dimensionality reduction, including ultrasensitive sensing [6][7][8][9][10][11][12], laser mode selection [13,14], chiral mode conversion [15][16][17][18], and unidirectional invisibility [19,20]. Harnessing these peculiar features of non-Hermitian degeneracies for building novel devices with unprecedented performance has been experimentally demonstrated in various classical dissipative platforms, ranging from nanophotonics [2,[21][22][23][24][25], acoustics [26] to macroscopic facilities, such as fiber network [27], electric circuits [28] and heat diffusive system [29].…”

Experimental demonstration of phase-matching and Sagnac effect in a millimeter-scale wedged resonator gyroscope

“…Chip-based devices are a mainstream of development in recent years, such as photon source [1], optical sensing [2], and quantum key distribution [3,4]. Gyroscopes for rotation sensing with high sensitivity and precision have been studied in various systems ranging from microoptical-electro-mechanical system [5,6], cold atom system [7,8], optomechanical system [9,10], photon and matter-wave interferometers [11,12], to solid spin system [13][14][15].…”

“…Whispering-gallery-mode (WGM) resonators as a crucial branch of optical systems have become a promising platform for both fundamental research [25,26] and practical applications [27][28][29][30][31][32][33][34] owing to the ability to enhance light-matter interaction in an ultra-small volume. Among these applications, WGM resonators play a significant role in sensing of different physical quantities such as nanoparticles [2,35,36], pressure [37], acceleration [38], and rotation velocity [39][40][41][42]. The highly efficient coupling [43][44][45][46] of light from conventional components to optical modes is a crucial factor in the development of chip-based devices.…”

“…In this experiment, the sensing unit includes a wedged resonator with a diameter of 2.5 mm and a Q factor of about 6 × 10 6 , which is available in conventional fabrication processing. (2) The design of the optical gyroscope based on the wedged resonator is highly integrated benefiting from the compatible fabrication technique of the wedged resonator. The experimental results verify Sagnac effect in the wedged resonator and provide the feasibility of developing gyroscopes in the WGM resonator system.…”