Diffraction and Scattering
It might make sense that waves travel in straight lines, but different conditions can cause them to change. One change occurs when light encounters another substance and is diffracted. The principle is straightforward enough to understand, and it plays a major role in how light travels down single-mode fibers, where the aperture is very small.
Diffraction occurs when a wave strikes an item shorter than its wavelength at which point the wave bends. The closer the aperture is to the wavelength, the greater the diffraction effect (see Figure 3.13).
Figure 3.13 Diffraction through a narrow aperture.
If light runs into other molecules, an effect called scattering can occur. Part of the light is deflected or scattered in different directions. How much of the light is scattered, and in which directions, depends on the type of scattering involved. We'll learn more about scattering when we study nonlinear effects of light propagating down a fiber.