What term describes the spreading out of modes in a light pulse as it travels through optical fiber?

The term that describes the spreading out of modes in a light pulse as it travels through optical fiber is dispersion. Dispersion occurs because different wavelengths of light travel at slightly different speeds through the fiber, which leads to the broadening of the pulse over distance. This phenomenon is crucial to consider in high-speed optical communication, as it can limit the maximum distance a data signal can travel without degradation.

The other terms listed have distinct meanings that do not apply in this context. Refraction refers to the bending of light as it passes from one medium to another, which does not account for mode spreading within the fiber itself. Reflection involves the bouncing back of light from a surface, which also does not pertain to the spreading of light pulses. Interference is the phenomenon that occurs when two or more light waves overlap and combine, creating patterns of constructive and destructive interference, which does not specifically relate to the dispersion of light modes in fibers. Therefore, dispersion is the accurate term that encapsulates the spreading out of light modes in an optical fiber.