One path that a light ray can travel through the glass core of an optical fiber is called a(n) _____.

A light ray traveling through the glass core of an optical fiber is referred to as a "mode." In the context of fiber optics, a mode represents a specific path that light can take as it propagates through the fiber's core, determined by the fiber's refractive index profile and the angle at which light enters the fiber. Each mode corresponds to a distinct electromagnetic field pattern and can carry information through the fiber.

This terminology is crucial in understanding how optical fibers operate, as each mode can support different propagation characteristics, including bandwidth and capacity. Depending on the type of fiber, various modes may exist, leading to different performance attributes for single-mode and multi-mode fibers.

Other terms listed, while related to fiber optics concepts, do not specifically define the path of a light ray. A "waveguide," for instance, refers to a structure designed to guide electromagnetic waves; it is a broader category that encompasses various types of guiding mechanisms, including optical fibers. "Pathway" and "signal route" are more general terms and do not convey the specific optical characteristics that a "mode" does within the realm of fiber optics. Understanding this distinction helps in grasping how light transmission works in optical fibers.