Resonant-cavity-enhanced photo detector
Resonant-cavity-enhanced photodetectors, also known as RCE photodetectors, are sensors designed to detect light or other forms of electromagnetic radiation. They achieve this by utilizing an optical cavity—a configuration of mirrors or other optical elements that forms a cavity resonator for light waves, allowing for more efficient targeting of specific wavelengths.
Source: Wikipedia — Resonant-cavity-enhanced photo detector (CC BY-SA 4.0)