Single mode fiber is an optical fiber designed to carry light only directly down the fiber. It is used mainly for long distance, high-speed data transmission. The most common wavelength used for single mode fiber is 1310nm. This wavelength is used because it has the lowest attenuation rate, meaning it can travel the longest distance with the least amount of signal loss. Single mode fiber is also used for high-speed data transmission, such as 10G Ethernet, 40G Ethernet, and 100G Ethernet. It is also used for applications such as fiber optic cable TV, fiber optic telephone systems, and fiber optic internet. Single mode fiber is the most reliable and cost-effective way to transmit data over long distances.