Which of the following describes the two types of optical fibers?

The correct answer describes the two types of optical fibers as step-index and graded-index.

Step-index fibers are characterized by a uniform core refractive index that abruptly changes at the boundary with the cladding, allowing light to reflect off this boundary at specific angles. This design is ideal for long-distance communication as it leads to lower modal dispersion.

Graded-index fibers, on the other hand, have a core where the refractive index gradually decreases from the center toward the cladding. This gradual change allows light rays to bend more gently as they travel, which improves the overall transmission of data by reducing modal dispersion, making graded-index fibers better suited for short to medium distances.

While other options mention terms related to optical fibers, they do not accurately define the two primary fiber types. For instance, "single-mode" and "multi-mode" refer to the number of light paths available in the fiber, while "core" and "cladding" describe the components of an optical fiber rather than the types. "Dual-mode" and "bi-mode" are not standard terms used in the context of optical fiber classification, which emphasizes why step-index and graded-index is the correct distinction.