Optical Fibre: Core (n=1.50) to Cladding (n=1.46) at 15°
In a typical optical fibre, the small refractive index difference between core and cladding causes total internal reflection to trap light.
How to use this tool
- Enter refractive index n₁, angle of incidence θ₁ and refractive index n₂ in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your angle of refraction θ₂ and the full breakdown beneath it.
Optical fibres guide light by keeping it inside the high-index core through total internal reflection at the core–cladding boundary.
Frequently asked questions
- What is total internal reflection?
- When light in a denser medium (e.g. glass) hits the boundary at an angle greater than the critical angle, all light is reflected back. This is the principle behind fibre-optic cables.
- What are common refractive indices?
- Vacuum/air: 1.0, water: 1.33, crown glass: 1.52, diamond: 2.42.