In fiber optic communication, what is cladding and why is it used around the fiber core?

Introduction / Context:
Fiber optic cables transmit data as pulses of light through very thin glass or plastic fibers. The internal structure of a fiber includes a central core and a surrounding cladding. Both parts play important roles in guiding light and maintaining signal quality. This question asks you to explain what cladding is and why it is necessary.

Given Data / Assumptions:

• A fiber optic strand has a central core through which light travels.
• The core is surrounded by cladding made of a different optical material.
• The refractive index of the cladding is slightly lower than that of the core.

Concept / Approach:
In fiber optics, light is guided along the core using the principle of total internal reflection. For this to happen, the core must have a higher refractive index than the surrounding material. The cladding is designed with a slightly lower refractive index so that light striking the core boundary at shallow angles is reflected back into the core instead of escaping. This guidance mechanism allows light pulses to travel long distances with low loss and reduced interference between adjacent fibers. The cladding also provides mechanical protection and helps maintain the correct numerical aperture of the fiber.

Step-by-Step Solution:
Step 1: Recognize that cladding is an integral optical layer, not just an external plastic jacket.Step 2: Recall that the refractive index of the cladding is intentionally made lower than that of the core.Step 3: Understand that this refractive index difference causes total internal reflection at the core cladding boundary.Step 4: Note that total internal reflection keeps light confined within the core, allowing efficient signal transmission.Step 5: Choose the option that correctly describes the cladding as a surrounding layer that helps guide light by total internal reflection.

Verification / Alternative check:
Fiber specifications often list core diameter, cladding diameter, and numerical aperture. For example, a common multimode fiber might be labeled 62.5 or 125, indicating a core of 62.5 micrometers surrounded by cladding of 125 micrometers. The difference in refractive indices is carefully controlled during manufacturing. Optical diagrams in textbooks show rays bouncing within the core because the cladding keeps them confined. These details confirm the role of cladding as described in the correct option.

Why Other Options Are Wrong:
Option B: Describes shielding in copper cables, not the optical cladding in fiber.Option C: Refers to an outer plastic jacket, which protects the cable mechanically but is not called cladding in optical terms.Option D: Talks about adhesive used during splicing, which is not the same as the structural cladding layer.

Common Pitfalls:
Students sometimes think of cladding as just mechanical protection. While it does contribute to strength, its primary role is optical, ensuring correct light guidance. Another pitfall is forgetting that the core and cladding must have specific refractive index values. If the indices are not properly chosen, the fiber will not guide light efficiently and losses will increase.

Final Answer:
The correct answer is An outer layer of glass or plastic surrounding the fiber core with a lower refractive index that keeps light signals confined within the core by total internal reflection.