What characteristic of optical fiber enables total internal reflection?

Total internal reflection in optical fiber is a phenomenon that occurs when light traveling through a medium reaches the boundary of a medium with a lower refractive index at an angle greater than the critical angle. The critical factor that enables this process is the difference in refractive indexes between the core and the cladding of the optical fiber.

In optical fibers, the core has a higher refractive index than the cladding. When light travels through the core and encounters the boundary with the cladding, it reflects back into the core instead of passing into the cladding, as long as the angle of incidence exceeds the critical angle. This is what allows the light to be guided along the fiber, facilitating efficient data transmission over long distances.

The other choices do not facilitate total internal reflection in the same significant way. The type of light source may influence how well the fiber transmits light, but it does not inherently enable reflection. The diameter of the fiber core affects signal strength and performance at different wavelengths, but it is not a direct cause of the total internal reflection phenomenon. Similarly, while the length of the fiber cable plays a role in attenuation and signal quality, it does not impact the fundamental mechanics of reflection occurring at the core-cladding boundary.