Optical fibers are designed for many different application scenarios. To understand the different applications, it is important to understand the properties of different fiber types.
Now let's look at two light rays that travel along a multimode fiber. One light ray travels straight down the fiber core center which is the shortest path. fiber isolator A second light ray travels at a steep angle and bounces back and forth by the fiber core side wall (a phenomenon called total internal reflection) while traveling down the fiber length which is a longer path than the first light ray.
Single mode fiber does have some disadvantages though. The smaller fiber core diameter makes it much harder to couple light into the fiber. This increases the manufacturing cost of many single mode fiber optic components such as isolator, attenuator, etc. The tolerances for single mode connectors, mechanical splices are also much more demanding.
Related Reading: optic isolator, high power isolator, polarization maintaining, PM coupler
