Two terms that often come up are routers and fiber optic internet, but they refer to very different parts of your network. Simply put, a router is a device that directs data traffic, while fiber is the physical medium that carries the data. If you're accessing the internet through fiber optics. An ONT (Optical Network Terminal) is used in fiber internet to convert light signals into data, while a modem is used in cable or DSL connections to modulate and demodulate signals. This difference in. Fiber cable modems and optical routers are essential components of modern broadband connectivity, providing fast and reliable internet access. In this guide, we'll explore the differences.