How does an optical fibre carry light around bends without leaking it out?
The light hits the fibre's inner wall at an angle greater than the critical angle, so it undergoes total internal reflection instead of escaping.
The light hits the fibre's inner wall at an angle greater than the critical angle, so it undergoes total internal reflection instead of escaping. It keeps bouncing along the core (which is denser than the cladding) all the way to the far end, even around gentle curves. The same total internal reflection makes a diamond sparkle and a mirage shimmer.
Key point
Total internal reflection traps the light inside the denser core.
Common mistake
thinking the light is guided by ordinary mirror coatings.
Memory tip
dense core + angle beyond critical → light stays trapped.
Tap to watch or see it right here — the app stays open (it only opens a quick search if nothing embeddable is found).