Single-mode fiber is a type of optical fiber designed to carry light directly down the fiber with minimal reflection. It has a small core diameter, typically around 8 to 10 micrometers, which allows only one mode of light to propagate. This design reduces signal loss and allows for longer transmission distances compared to multi-mode fiber. Single-mode fiber is commonly used in telecommunications and data networks, where high bandwidth and long-distance communication are essential. Its ability to transmit data over vast distances makes it ideal for applications like internet backbones and fiber-to-the-home installations.