In an optical fiber cable, what creates the reflective boundary?

In an optical fiber cable, the reflective boundary is created by the cladding. The structure of the optical fiber consists of a core and cladding, where the core has a higher refractive index compared to the cladding. This difference in refractive indices is fundamental to the phenomenon of total internal reflection, which allows light to be guided through the core of the fiber.

When light travels into the core, if it hits the boundary with the cladding at an angle greater than the critical angle, it reflects back into the core rather than passing into the cladding. This enables the efficient transmission of light signals through the fiber over long distances with minimal loss. The cladding also serves as a protective layer, but its primary role regarding the reflective boundary is to facilitate this total internal reflection, ensuring that the light stays contained within the core to maintain signal integrity and performance.

While the core material is crucial for conducting light, and the sheath and buffer coating have protective and structural roles, it is specifically the cladding that establishes the reflective boundary essential for the fiber's functionality.