How Does This Sensor Resonate with You?

Sensors serve as the eyes and ears of modern technology, enabling the collection of crucial data from numerous sources. Without these sensors, many of the devices that we rely on in our daily lives would not exist. In medical diagnostics, for example, sensors provide real-time and precise information for disease diagnosis, patient monitoring, and treatment management. Similarly, in environmental monitoring, sensors are essential for tracking air quality, water purity, and soil composition.

Beyond these applications, sensors are also finding their way into a wide range of other use cases in manufacturing, self-driving vehicles, security systems, and much more. But for these applications to be useful, the sensors must be able to do their job with a high level of accuracy and sensitivity. While many excellent sensing technologies exist today, there are still applications for which no suitable solutions exist.

Whispering-gallery-mode (WGM) resonators have been proposed as a potential solution that might help to fill this gap. They confine and concentrate light in a very small, circular path, then when the sensor encounters a molecule of interest, the resonant frequency of the circulating light is altered, which can be measured to detect the molecule's presence. WGM resonators exhibit characteristics that could make them perfect for many high-resolution optical sensing applications. But despite their promise, these devices have proven to have a narrow dynamic range, limited resolution, and inadequate levels of accuracy in practice.

A new approach developed by researchers at Washington University in St. Louis may move the technology beyond these present limitations. By utilizing a sort of optical barcode, it was demonstrated that WGM sensors can monitor multiple wavelengths of light simultaneously, whereas existing devices cannot differentiate between them. This enables the devices to pick up multiple resonance changes caused by a particle, which serves to increase the sensitivity and accuracy of the system.

Calculations showed that the new multimode WGM resonator has a 350 times greater sensing range than is possible with existing technologies. And that greater sensing range means that far more data is being collected, which could be useful in a wide range of applications in biomedical, chemical, and environmental monitoring systems, for example.

Jie Liao, a postdoctoral research associate involved in the study summarized their work by saying that “WGM resonators’ ultrahigh sensitivity lets us detect single particles and ions, but the potential of this powerful technology has not been fully utilized because we can’t use this ultrasensitive sensor directly to measure a complete unknown. Multimode sensing enables that look into the unknown. By expanding our dynamic range to look at millions of particles, we can take on more ambitious projects and solve real-world problems.”