Bold claim: polarized light could make wearable sensors fairer for all skin tones.
Photoplethysmography (PPG) is the optical method behind everything from hospital pulse oximeters to consumer wearables that monitor heart rate, sleep, and oxygenation. Yet PPG readings vary across individuals, especially by skin color. Higher melanin content in darker skin absorbs and scatters light, which can lead to less reliable measurements. This mismatch has been linked to less accurate blood-oxygen readings for people with more melanin.
Most attempts to improve PPG rely on software fixes—better filters or machine-learning tricks to clean up signals disrupted by movement or poor contact. But these fixes generally address noisy data rather than fix the root cause: how light interacts with tissue. A Brown University team has tested a different path. In a study published in Biophotonics Discovery, researchers target the problem at its source: the light–tissue interaction itself.
They developed a wearable, polarization-sensitive PPG sensor that leverages the light’s electric-field orientation to favor signals from deeper blood vessels while reducing interference from superficial layers rich in melanin. The device splits light into two channels: co-polarized light (aligned with the incoming beam) and cross-polarized light (perpendicular). This setup helps suppress superficial scattering and amplify signals from deeper tissue.
Tests on volunteers with light, medium, and dark skin tones showed that the cross-polarized configuration consistently yielded higher perfusion index (PI) values, a proxy for signal strength, at both red (655 nm) and infrared (940 nm) wavelengths. The improvement was especially notable for darker skin at the red wavelength.
The researchers caution that these results are preliminary and that a larger study is planned. Still, the approach could help reduce bias in PPG-based technologies and pave the way for more inclusive medical and consumer wearables.
“Most PPG devices focus on innovations in digital signal processing,” said senior author Kimani C. Toussaint, Jr. “But as optics researchers, we’re exploring what can be achieved by engineering the light itself. We believe we’re only scratching the surface of a potentially new, more accurate way to obtain higher-quality PPG signals.”
For full details, see the original Gold Open Access article by R. Jakachira et al., “Evaluation of a polarization-sensitive, dual-wavelength wearable photoplethysmography sensor across a range of skin tones,” Biophotonics Discovery, 3(1), 012509 (2025), doi: 10.1117/1.BIOS.3.1.012509.
Note: This material is provided by the originating organization/author and has been edited for clarity and length. Mirage.News does not take institutional positions; the views expressed are solely those of the authors. View the full release here: https://www.miragenews.com/polarized-light-enhances-wearable-sensors-for-1587360/
