Say we want to shine a flashlight beam down a long, straight hallway at the other end, just point the beam straight down the hallway, the light travels in a straight line, and we know it‘s fine. What if the corridor has a bend? At this time, a mirror can be placed at the corner to reflect the beam at the corner. What if the hallway is very winding, with multiple bends? It is also possible to line the walls with mirrors and angle the beam of light so that it bounces from side to side along the hallway. This is exactly what happens when light travels through an optical fiber, but the light is totally reflected in the fiber.

However, when the light is transmitted in the optical fiber, when the optical fiber is bent, the number of back and forth reflections increases, and the angle of reflection also increases. As long as the bending is not particularly severe, the light will not leak out of the fiber, so we usually have certain restrictions on the bending of the fiber. In addition, we know that ordinary optical fibers are divided into single-mode and multi-mode optical fibers. What is the difference in their transmission methods, the following figure can be very intuitive display.