A device for electrically isolating networking components that are joined by long runs of copper cabling. Opto isolators prevent ground loops from damaging networking components.
When a network component or cable transmitting a signal is connected to one port on an opto isolator, the signal is converted briefly into light and then back into an electrical signal before exiting through the other port on the opto isolator. This brief metamorphosis from electric current into light and back again breaks the electrical connection between the two ports of the device, allowing the signal (alternating current) to flow but preventing direct current from flowing along the cable.
Opto isolators are commonly used in RS-232 serial connections between mainframe hosts and terminals connected by long cables. Opto isolation is typically built into line drivers for serial communication, so separate opto isolators are not required.