Components, circuits, or systems that convert between electrical and optical (light) energy.
Optoelectronics deals with electrical interfaces to light sources and/or light receivers.
Optoelectronics are often used in control circuits where electrical isolation is required between the source and the receiver (optocoupler) or to convey visible information to a human (LED).
Since optoelectronics is a broad topic, it makes sense to also include some lower-level tags as part of the question. Some examples: