What is the main requirement in fabricating optical fibres ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Optical Fibers:**
Optical fibers are thin, flexible tubes made of glass or plastic that transmit data in the form of light pulses. They are widely used for communication purposes, such as internet and telephone signals.

2. **Principle of Operation:**
The operation of optical fibers is based on the principle of Total Internal Reflection (TIR). This means that when light travels through the fiber, it reflects off the walls of the fiber without escaping, allowing the light to travel long distances.

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