Optical signals are transmitted directly without repeater amplification. Gigabit single-mode single-core optical fiber modules usually have the following specifications: multi-mode 550m, single-mode 15km, 40km, 80km, 120km, etc. Fiber optic transmission distance varies based on fiber type, environmental conditions, and equipment selection. There are three main reasons for this: First, high-bandwidth. 1) 850nm (MM, multi-mode, low cost, but short transmission distance, usually only 500M); 2) 1310nm (SM, single mode, large loss during transmission, small dispersion, generally used for transmission within 40KM); 3) 1550nm (SM, single mode, small loss during transmission, but large dispersion.