Enhanced sensitivity operation of an optical gyroscope near an exceptional point

Abstract: Exceptional points (EPs) are special spectral degeneracies of non-Hermitian Hamiltonians governing the dynamics of open systems. At the EP two or more eigenvalues and the corresponding eigenstates coalesce. Recently, it has been proposed that EPs can enhance the sensitivity of optical gyroscopes. Here we report measurement of rotation sensitivity boost by over 4X resulting from operation of a chip-based stimulated Brillouin gyroscope near an exceptional point. A second-order EP is identified in the gyroscope and originates from the dissipative coupling between the clockwise and counterclockwise lasing modes. The modes experience opposing Sagnac shifts under application of a rotation, but near the exceptional point new modal admixtures dramatically increase the Sagnac shift. Modeling confirms the measured enhancement. Besides the ability to operate an optical gyroscope with enhanced sensitivity, this result provides a new platform for study of non-Hermitian physics and nonlinear optics with precise control.

• The paper achieves a 4-fold sensitivity enhancement by operating near a second-order exceptional point, significantly improving gyroscopic rotation detection.
• It employs a high-Q silica wedge resonator with dual pump Brillouin lasers to precisely control mode coupling and analyze CW/CCW eigenmode behavior.
• Experimental findings validate theoretical predictions, highlighting the vital role of dissipative coupling in advancing precision metrology in optical sensors.

Enhanced Sensitivity Operation of an Optical Gyroscope Near an Exceptional Point

This paper presents an in-depth analysis of operating an optical gyroscope near an exceptional point (EP), specifically within a chip-based stimulated Brillouin gyroscope framework. The research highlights a significant enhancement in rotation sensitivity, quantified by a factor of over 4 times, attributed to the presence of a second-order EP. The EPs in question arise from the dissipative coupling between clockwise (CW) and counterclockwise (CCW) lasing modes. This research advances the understanding of non-Hermitian physics and its practical implications for sensor enhancement, leveraging the unique properties of EPs.

Methodological Overview:

The experimental setup features a high-quality-factor ($Q\approx10^8$) silica wedge resonator, providing the necessary conditions for investigating the effects of EPs on rotation sensitivity. The gyroscope employs counter-propagating Brillouin lasers, activated by dual pumps of varied frequencies injected into the resonator. The researchers meticulously controlled the pump detuning frequency to study the impact of mode pulling and frequency shifts, which are critical to the dynamic response of the system near the EP.

By analyzing the eigenmodes and their response to perturbations through a non-Hermitian Hamiltonian framework, the research delineates how exceptional points can be used to augment the sensitivity of optical gyroscopes. The study leverages both experimental data and theoretical modeling to validate the effects of EPs, illustrating a compelling congruence between measured outcomes and predicted behaviors.

Key Findings and Numerical Results:

1. Sensitivity Enhancement:
   • The study achieved a 4-fold increase in sensitivity near the EP, bolstered by a square-root response curve that governs the system's transduction capabilities. This enhancement underscores the potential of non-Hermitian dynamics in advancing precision measurement technologies.
2. Mode Coupling:
   • The dissipative coupling, with a critical frequency $\Delta\omega_c$ calculated through the Hamiltonian model, plays a crucial role in regulating this enhancement. The analysis demonstrates that EP-induced mode coalescence can result in notable changes in the Sagnac shift magnitude.
3. Eigenmode Characterization:
   • By examining the photonic eigenmodes, both theoretically and through spectral measurements, the study identifies shifts in the CW and CCW modes as a direct outcome of varying the detuning frequency. This elucidates the underlying mechanisms through which EPs govern enhanced gyroscopic performance.

Theoretical and Practical Implications:

• The research contributes to nonlinear optics and non-Hermitian physics by providing empirical evidence of EPs facilitating sensitivity enhancements in optical sensors.
• Practically, this work promises advancements in on-chip sensor technology, indicating that systems leveraging EPs could yield superior performance in diverse measurement contexts, such as inertial navigation systems and environmental sensing.

Future Directions:

The findings invite further exploration into:

• Optimizing sensor configurations seeking maximum EP exploitation while mitigating any adverse effects of noise, which appears increasingly pronounced near the EP.
• Extending the application of EPs to other photonic systems where enhanced mode sensitivity could engender new functionalities or improve existing technologies.

In conclusion, this paper successfully integrates theoretical modeling with experimental validation to uncover the capabilities of exceptional points in enhancing the sensitivity of optical gyroscopes. This research not only addresses a fundamental scientific question but also opens avenues for tangible technological innovations in precision metrology.