Opto-electronic oscillator
In optoelectronics, an opto-electronic oscillator (OEO) is a circuit that produces a repetitive electronic sine wave and/or modulated optical continuous wave signals. An opto-electronic oscillator is based on converting the continuous light energy from a pump laser to radio frequency (RF), microwave or mm-wave signals.
Source: Wikipedia — Opto-electronic oscillator (CC BY-SA 4.0)