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. To connect your fiber optic cable to a router, ensure you have the following: Fiber optic modem (ONT): Most fiber connections require an Optical Network Terminal (ONT), provided by your ISP. There are several types of connectors, including LC, SC, and ST. Routers designed for DSL (which uses phone line inputs) or cable (which uses coaxial inputs) won't work.