Moisture-Insensitive Optical Touch Sensors

An electronic device, comprising:

• a display;
• a display cover layer through which the display presents images;
• light detectors configured to detect a finger touch on the display cover layer;
• a light source that emits light into the display cover layer, wherein the light is guided within the display cover layer via total internal reflection;
• and
• a metasurface grating on a lower surface of the display cover layer, wherein the metasurface grating redirects the light within the display cover layer to sustain the total internal reflection and wherein the total internal reflection is locally defeated by the finger touch to scatter the light towards the light detectors.

An electronic device, comprising:

• a display;
• a display cover layer through which the display presents images;
• light sensors configured to detect a finger touch on the display cover layer;
• an array of light-emitting elements that emit light in different directions towards a lower surface of the display cover layer;
• and
• a metasurface grating interposed between the array of light-emitting elements and the display cover layer, wherein the metasurface grating couples the light into the display cover layer at an angle such that the light propagates within the display cover layer via total internal reflection, wherein the metasurface grating comprises first metasurface structures optimized to receive the light from a first of the light-emitting elements and second metasurface structures optimized to receive the light from a second of the light-emitting elements, and wherein the total internal reflection is locally defeated by the finger touch to scatter the light towards the light sensors.