Which fiber-optic cable type reduces modal dispersion through its design?

Which fiber-optic cable type reduces modal dispersion through its design?

• A. Single-mode
• B. Graded index
• C. Step index
• D. Low water peak

Answer: (B)

The type of fiber-optic cable that effectively reduces modal dispersion is graded index fiber. This design features a varying refractive index along the core of the fiber, which causes light rays traveling at different angles to take different paths. As a result, the rays that travel longer paths (more obliquely) travel more slowly due to the higher refractive index in the core's center, while those traveling straight through experience less delay. This gradual change in the refractive index helps to ensure that the light waves arrive at the end of the fiber more uniformly, significantly minimizing modal dispersion. In contrast, single-mode fibers utilize a smaller core diameter and allow only one mode of light to propagate, which naturally eliminates modal dispersion, but does not leverage design variations in the refractive index to mitigate it. Step index fibers do not have a graded structure and are more susceptible to modal dispersion because they lack the gradual index transition, leading to quicker losses associated with light paths. Low water peak fibers refer to a specific feature where water absorption bands in glass are minimized, affecting attenuation rather than directly addressing modal dispersion.

The type of fiber-optic cable that effectively reduces modal dispersion is graded index fiber. This design features a varying refractive index along the core of the fiber, which causes light rays traveling at different angles to take different paths. As a result, the rays that travel longer paths (more obliquely) travel more slowly due to the higher refractive index in the core's center, while those traveling straight through experience less delay. This gradual change in the refractive index helps to ensure that the light waves arrive at the end of the fiber more uniformly, significantly minimizing modal dispersion.

In contrast, single-mode fibers utilize a smaller core diameter and allow only one mode of light to propagate, which naturally eliminates modal dispersion, but does not leverage design variations in the refractive index to mitigate it. Step index fibers do not have a graded structure and are more susceptible to modal dispersion because they lack the gradual index transition, leading to quicker losses associated with light paths. Low water peak fibers refer to a specific feature where water absorption bands in glass are minimized, affecting attenuation rather than directly addressing modal dispersion.