Modeling light propagation for under-display sensing in a smartphone.

Area of Science:

• Optics and Photonics
• Electrical Engineering
• Materials Science

Background:

• Bezel-less smartphones rely on under-display sensing (UDS) for features like ambient light sensors (ALS), cameras (UDC), and proximity sensors.
• Light distortion through display panels significantly degrades UDS signal quality, necessitating accurate light propagation modeling.
• Existing models struggle to universally address the varied light propagation phenomena affecting different UDS components.

Purpose of the Study:

• To propose a universal model for analyzing light propagation in under-display sensing systems.
• To accurately categorize UDS components (ALS, UDC, proximity sensors) into distinct light propagation regimes.
• To validate the model's effectiveness using experimental data from a commercial smartphone.

Main Methods:

• A universal light propagation model based on the Fresnel number is developed to classify UDS regimes.
• Simulations are performed for under-display ambient light sensors (geometric optics), under-display cameras (Fraunhofer diffraction), and proximity sensors (Fresnel diffraction).
• Experimental validation is conducted on a commercial smartphone, comparing simulation results with measured data for accuracy.

Main Results:

• The model correctly identifies ALS, UDC, and proximity sensors operating in geometric optics, Fraunhofer diffraction, and Fresnel diffraction regimes, respectively.
• Simulations accurately predict angular response attenuation for ALS and image blurring for UDC, with experimental data showing high agreement.
• Fresnel diffraction analysis for proximity sensors reveals an optimal sensor-detector orientation of 45 degrees and confirms the model's superiority over geometric optics.

Conclusions:

• The proposed Fresnel number-based model provides a unified framework for understanding and optimizing light propagation in UDS.
• The model's experimental verification on a commercial smartphone demonstrates its practical applicability for designing improved UDS.
• This research offers crucial insights into light propagation challenges within smartphone displays, guiding future UDS development.