What is Optical fiber? — Physics

Definition 3.19 High School Physics · Chapter 3 — Refraction of Light

An optical fiber is a thin glass thread made of a core of index $n_1$ wrapped in a cladding of slightly smaller index $n_2 < n_1$ . Light injected at one end travels along the core by repeated total internal reflection on the core–cladding boundary.

Light guided along the core of a fiber by total internal reflection (bounce angles greatly exaggerated: real rays graze the wall at more than 80 from the normal). — Light guided along the core of a fiber by total internal reflection (bounce angles greatly exaggerated: real rays graze the wall at more than $80^\circ$ from the normal).

Examples

Example 3.20 (A fiber by the numbers)

With $n_1 = 1.48$ and $n_2 = 1.46$ ,

\sin i_c = \frac{1.46}{1.48} = 0.986, \qquad i_c = 80.6^\circ :

only rays within about $9^\circ$ of the axis are guided — which is fine, since that is exactly how laser light is injected. Inside the core the light travels at $v = c/1.48 = 2.03 \times 10^{8}\,\mathrm{m}/\mathrm{s}$ : a pulse crosses a $100\,\mathrm{km}$ fiber in about half a millisecond.

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Examples

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