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 results in lower signal attenuation and higher bandwidth over long distances compared to multi-mode fiber. Due to its efficiency, single-mode fiber is commonly used in telecommunications and data networks. It is ideal for long-distance communication, such as connecting cities or data centers, as it can transmit data over several kilometers without significant loss of quality.