Single-mode & Multi-mode

      The simplest type of optical fiber is called SINGLE-MODE. It has a very thin core about 5-10 microns (millionths of a meter) in diameter. In a single mode fiber, all signals travel straight down the middle without bouncing off the edges ( the red line in the diagram explains) Cable TV, Internet and telephone signals are generally carried by single-mode fibers, wrapped together into a huge bundle. Cables like this can send information over 100 km (60 miles).
     

Another type of fiber optic cable in called MULTI-MODE. Each optical fiber in a multi-mode cable in about 10 times bigger than on in a single-mode cable. This means light beams can travel through the core by following a variety of different paths (The purple, green, and blue lines are example) in other words in multiple different mode. Multi-mode cables can send information only over relatively short distances and are used to link computer network together.