Final answer:
The type of fiber used to reduce modal dispersion in fiber optics is one with a cladding material that has a lower index of refraction than the core, ensuring total internal reflection and efficient light transmission.
Step-by-step explanation:
The type of fiber that uses numerous concentric layers of glass to reduce modal dispersion is a type designed for fiber optics transmission. In fiber optics, light is transmitted down fibers made of plastic or glass by applying the principle of total internal reflection. To ensure this reflection, even when fibers are in contact, the core of the fiber is surrounded by a cladding material with a lower index of refraction than the core itself. This cladding acts as a barrier to prevent light from escaping out of the fiber, ensuring that most of the light is propagated along the length of the fiber, which minimizes the loss of signal and helps maintain a quality image at the other end. In addition to the cladding, fibers feature a protective layer that makes them both flexible and durable.