CEA-Leti has developed a new optical sending architecture that combines a microLED and an organic photodetector (OPD). This system-level approach, that combines device design, electronics, and modeling allows for multifunctional display applications, without compromising display performance.
The researchers have optimized both devices to a green wavelength, that is relevant to photoplethysmography (PPG) signal extraction.
The researchers designed a dedicated electronic platform enabling full end-to-end characterization of the complete signal chain—from microLED driving, through a device under test, to photodetection and readout circuitry. Lock-in detection techniques were implemented to improve signal-to-noise ratio and suppress static parasitic components. This is particularly relevant for biosensing detection where AC/DC ratio should be enhanced.
System validation was performed using optical phantoms engineered to replicate the absorption and scattering properties of biological tissue. This approach provided a controlled and repeatable environment for assessing biosensing performance under realistic conditions. Experimental results were combined with analytical modeling to derive a closed-form expression linking microLED operating conditions, photodetector responsivity, and device-under-test reflectance to the detected signal.
Characterization platform including custom electronic board and biological phantom mimicking human tissues
The co-packaged microLED devices demonstrated optical power up to 12 mW at a wavelength of 525 nm. On the detection side, OPD responsivity was tuned by adjusting the thickness of the ZnPc active layer to align with the microLED emission peak, achieving a responsivity of 0.083 A/W at the wavelength of interest.
