Step index, in fiber optics, is a refractive index profile with a uniform refractive index throughout the core and a sharp decrease at the core-cladding boundary.
Step index describes a type of optical fiber in which the refractive index is uniform, or constant, throughout the core, then decreases sharply, in a single step, at the boundary between the core and the cladding. This abrupt change in refractive index is what confines light within the core by total internal reflection. Step index is one of the basic fiber profiles, in contrast to graded index fiber, where the index changes gradually across the core.
Because the index changes abruptly at the boundary, light rays in a step index multimode fiber can travel many distinct paths of different lengths, which contributes to modal dispersion. Single-mode fibers also use a step index profile but, with their very small core, support only one path. The profile is fundamental to how a fiber guides light.
In commercial and industrial fiber systems, the refractive index profile, including step index, affects how a fiber performs. Recognizing the term helps in understanding how fiber guides and disperses light.
Because the abrupt change in refractive index at the boundary lets light rays in a step index multimode fiber travel many distinct paths of different lengths, the profile contributes to modal dispersion, while single-mode fibers use a step index but support only one path.
At Windy City Wire, the focus on fiber optic cable for commercial communication connects to fiber characteristics like the step index profile. Understanding how the index profile guides light helps customers appreciate how fiber construction affects performance across their communication links.