In an optical fibre, the light signal is transmitted by

Options

A. Refraction at the core-cladding interface
B. Interference between the incident and inflected waves
C. Repeated total internal reflections at the core and cladding interface
D. Polarisation of optical signals.

Answer

### Step-by-Step Solution:

1. **Understanding Optical Fiber Structure**:
- An optical fiber consists of two main parts: the core and the cladding. The core is the central part where light travels, while the cladding surrounds the core and has a lower refractive index.

2. **Refractive Indices**:
- The refractive index of the core is denoted as \( \mu_1 \) and that of the cladding as \( \mu_2 \). Typically, \( \mu_1 > \mu_2 \), meaning the core is a denser medium compared to the cladding.

3. **Total Internal Reflection (TIR)**:
- The light signal in the optical fiber is transmitted through a phenomenon known as total internal reflection. This occurs when light travels from a denser medium (core) to a rarer medium (cladding) at an angle greater than the critical angle.

4. **Critical Angle**:
- The critical angle is the minimum angle of incidence at which total internal reflection occurs. For TIR to happen, the angle of incidence must be greater than this critical angle.

5. **Condition for TIR**:
- For total internal reflection to occur at the interface of the core and cladding, the light must strike the boundary at an angle greater than the critical angle. This ensures that the light is reflected back into the core rather than refracting into the cladding.

6. **Minimizing Loss**:
- The design of optical fibers is such that the relative refractive index is adjusted to keep the critical angle low, allowing maximum light to undergo total internal reflection. This minimizes energy loss during transmission.

7. **Conclusion**:
- Therefore, the light signal in an optical fiber is transmitted by repeated total internal reflections at the core and cladding interface. This ensures efficient transmission of light with minimal loss.

### Final Answer:
The light signal is transmitted by repeated total internal reflections at the core and cladding interface.

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