What is the most common configuration of an optoisolator or optocoupler?
A lens and a photomultiplier
A frequency-modulated helium-neon laser
An amplitude-modulated helium-neon laser
An LED and a phototransistor✓Correct answer
Explanation
An optoisolator is normally an LED facing a phototransistor inside one opaque package, so the signal crosses the gap as light and the two circuits share no conductive path. Photomultipliers and helium-neon lasers are laboratory instruments, not the contents of a small isolator package.