Optical Fibre: Light Guided by Total Internal Reflection

Theory

Light entering the end of a glass rod hits the side walls at angles larger than the critical angle ${\theta }_c=\arcsin (n_2/n_1)$, so it is totally reflected again and again and stays trapped inside. Real fibres use a core with a higher index than the cladding and carry data as light pulses over thousands of kilometres.

What to observe

• The beam zigzags along the rod without escaping.

Try this

• Rotate the laser: at steep angles the light leaks out of the rod.
• Lower the glass index to 1.2 and watch the light escape.

Also available in: Fibra óptica: luz guiada por reflexão interna total (Português) · Fibra óptica: luz guiada por reflexión interna total (Español)