Fiber optic cables carry data as pulses of light through hair-thin strands of glass or plastic. There is no physical or electrical compatibility between the two. Yes, you can often use your existing router with fiber optic internet, but there are crucial considerations. Understanding compatibility, potential limitations, and when an upgrade is necessary will ensure you get the most out of your high-speed connection. This guide will break down everything you. Fiber internet sounds like an entirely different technology from the cable or DSL connections most people grew up with — and in some ways, it is. Instead of a modem, fiber connections require an Optical Network Terminal (ONT), a device that converts fiber signals into an Ethernet connection.