In optical fiber cable, the information-modulated light signal is carried by the _____.

• A. Buffer
• B. Cladding
• C. Outer jacket
• D. Core

Answer: (D)

The information-modulated light signal travels through the core of the optical fiber. The core is the central region with a higher refractive index, which keeps the light confined and guided along the fiber by total internal reflection at the boundary with the surrounding cladding. The cladding surrounds the core and has a lower refractive index, which prevents the light from leaking out. Protective layers such as the buffer and outer jacket exist to shield the fiber, not to carry the signal. So, the core is where the data-carrying light actually propagates.