New Platform Brings Exceptional Point Enhancement to Existing Sensors

Optical sensors are fundamental to many scientific and technological projects, ranging from the detection of gravitational waves to the imaging of biological tissues for diagnostic purposes in medicine.

These sensors use light to identify variations in the properties of the environment they are monitoring, such as chemical biomarkers and physical changes in temperature. A recurring problem in optical sensing has been increasing the sensitivity to identify weak signals in the presence of noise.

The potential of exceptional points (EPs) for advanced optical sensing has been unlocked by new research from Lan Yang, the Edwin H. & Florence G. Skinner Professor in the Preston M. Green Department of Electrical & Systems Engineering in the McKelvey School of Engineering at Washington University in St. Louis.

In the study published on April 5th, 2024, in Science Advances, Yang and Wenbo Mao, a Doctoral Student in Yang’s lab and the study's first author, demonstrated that these unique EPs—specific conditions in systems where extraordinary optical phenomena can occur—can be utilized on conventional sensors to achieve remarkable sensitivity to environmental perturbations.

Yang and Mao created an EP-enhanced sensing platform to overcome the drawbacks of earlier methods. They have developed an innovative system with an EP control unit that can plug into physically separated external sensors, in contrast to traditional methods that require modifications to the sensor itself. With this setup, EPs can be fine-tuned only by adjusting the control unit, enabling ultrahigh sensitivity without requiring intricate sensor modifications.

We’ve implemented a novel platform that can impart EP enhancement to conventional optical sensors. This system represents a revolutionary extension of EP-enhanced sensing, significantly expanding its applicability and universality. Any phase-sensitive sensor can acquire improved sensitivity and reduced detection limit by connecting to this configuration. Simply by tuning the control unit, this EP configuration can adapt to various sensing scenarios, such as environmental detection, health monitoring, and biomedical imaging.

Lan Yang, Edwin H. & Florence G. Skinner Professor, Preston M. Green Department of Electrical & Systems Engineering, McKelvey School of Engineering, Washington University in St. Louis

Yang and Mao successfully avoided strict physical requirements for operating sensors at EPs, which have so far prevented their widespread adoption. They achieved this by separating the sensing and control functions.

This paves the way for EP enhancement to be implemented across a broad spectrum of conventional sensors, such as ring resonators, thermal and magnetic sensors, and those designed to detect vibrations or biomarker perturbations. This would significantly enhance the detection limit of sensors already used by scientists. By setting the control unit to an EP, the sensor can operate differently, not necessarily at an EP, while capitalizing on EP enhancement's advantages.

Yang’s team evaluated a system’s detection limit (that is, its capacity to distinguish minute perturbations over system noise) as a proof-of-concept. Comparing their EP-enhanced configuration to a conventional sensor, they showed a six-fold reduction in the detection limit.

With this work, we’ve shown that we can significantly enhance our ability to detect perturbations that have weak signals. We’re now focused on bringing that theory to broad applications. I’m specifically focused on medical applications, especially working to enhance magnetic sensing, which could be used to improve MRI technology. Currently, MRIs require a whole room with careful temperature control. Our EP platform could be used to enhance magnetic sensing to enable portable, bedside MRI.

Wenbo Mao, Study First Author and Doctorate Student, Washington University in St. Louis

Journal Reference:

Mao, W., et al. (2024) Exceptional–point–enhanced phase sensing. Science Advances.

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