A hair-thin thread of ultra-pure glass that guides light — and your data — across kilometres with almost no loss. Here's how a strand of glass became the backbone of the internet.
A fiber has a light-carrying core surrounded by cladding with a slightly lower refractive index. When light meets that boundary at a shallow angle it reflects entirely back inward — total internal reflection. The ray keeps bouncing along the core, staying trapped inside the glass all the way to the far end, even around gentle bends.
Three layers do the work. The core — about 9 µm across in single-mode fiber — carries the light. The cladding (125 µm) reflects it back in. A protective coating shields the glass from moisture and micro-cracks. The glass itself is purer than window glass by orders of magnitude: you could see clearly through kilometres of it.
The core's width decides how light travels. A narrow single-mode core lets light take just one path — ideal for long distances and high bandwidth. A wider multimode core lets light take many paths (modes) at once; those paths have slightly different lengths, so a pulse spreads out over distance — modal dispersion — which limits reach.
9 µm core · one path · long-haul, 1310 & 1550 nm
50–62.5 µm core · many paths · short reach, 850 nm
No glass is perfect. Light is slowly lost to absorption (molecules soaking up energy) and scattering (tiny density variations). Loss is measured in decibels per kilometre, and it depends on wavelength — which is why long-haul systems work in the low-loss windows around 1310 nm and 1550 nm, where a modern fiber loses only about 0.2 dB/km.
The Fiber Optic Lab turns these concepts into hands-on instruments you can practise safely — no fragile fiber, no costly gear. Log in to the suite to try them.
Confidential — prototype under development. This prototype and all associated content are the proprietary and confidential property of Daw Alfada, shared solely for authorized technical review. Any unauthorized copying, redistribution, reverse engineering, or commercial use — in whole or in part — is strictly prohibited. © 2026 Daw Alfada. All rights reserved.
