How do optical isolators function in a circuit?

Optical isolators function by allowing light to pass in one direction while preventing it from passing in the opposite direction. This is typically accomplished using components such as a light-emitting diode (LED) and a photodetector. In many applications, a small infrared LED serves as the source of light, which, when activated, transmits light to a photodetector on the other side of the isolator. This directional light transmission helps to isolate different parts of a circuit, ensuring that signals can be sent without feedback or interference from the receiving side.

In contrast, the other methods listed would not provide the same functional characteristics as optical isolators. Electromagnetic fields are used in different types of isolation devices, such as transformers, but do not serve the specific purpose of optical isolation. Mechanical switches can control signals, but they do not provide the non-contact isolation that optical isolators offer. Resistive elements can limit current but do not function to isolate circuits in the same manner as an optical system. Therefore, the use of a small infrared LED is key to the operation of optical isolators in a circuit.