Optical fiber works on the principle of –

SOLUTION

CONCEPT:

• Optical fibers are transparent fibers and act as a light pipe to transmit light between its two ends. They are made up of silicon dioxide.

• The total internal reflection occurs when the angle of incidence is greater than the critical angle.
• In optical fiber glasses of a high and lower index are assembled in the precise order.
• The light comes in from one end of the fiber and after thousands of successive internal reflections, the light reaches the opposite end of the fiber with almost zero loss. 

EXPLANATION:

• The refractive index of the material of the core (μ1) is higher than that of the cladding (μ2).
• When the light is incident on one end of the fiber at a small angle, the light passes inside, undergoes repeated total internal reflections along with the fiber, and finally comes out.
• Hence, the function of the cladding is to provide a lower refractive index at the core interface in order to cause reflection within the core so that light waves are transmitted through the fiber.
• Thus, cladding is used in the optical fiber in order to cause total internal reflection. Therefore option 1 is correct.