Question

Which property of light is used in an optical fiber?

• A. Interference
• B. Total internal reflection
• C. Diffraction
• D. Scattering

Hint:

Key points to remember:
1. Critical angle $\theta_c = sin^{-1}(n_2/n_1)$, where $n_2<n_1$

2. Optical fibers use step-index or graded-index profiles

3. Numerical aperture determines light acceptance angle

4. Total internal reflection enables low-loss transmission

Answer 1

The Correct Option is B

Step 1: Understanding optical fiber working principle
Optical fibers work by guiding light through a thin glass or plastic core surrounded by cladding with a lower refractive index. The key phenomenon that enables this is total internal reflection.
Step 2: Total internal reflection condition
Total internal reflection occurs when: 1. Light travels from a denser medium (higher refractive index) to a rarer medium (lower refractive index) 2. The angle of incidence is greater than the critical angle $(\theta>\theta_c)$
Step 3: Application in optical fibers
- The core has higher refractive index than cladding - Light entering at proper angles undergoes repeated total internal reflections - This allows light to travel long distances with minimal loss
Why other options are incorrect:
(a) Interference - not the primary principle used
(c) Diffraction - causes signal dispersion, which is undesirable
(d) Scattering - causes signal loss, not the desired effect