====== Fiber Optics ======

==== General information ====

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**The speed of light in free space is $c = 3.10⁸ (m/s)$**

Fiber optics propagate light using the **[[https://en.wikipedia.org/wiki/Refraction|refractive index]]** of different materials. 

It is the ratio of the speed of light in free space to the speed of light in a given material.
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In fiber-optics, spectrum notation is generally stated in wavelength ($nm$) over frequency ($Hz$) because it is easier to use.

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$\lambda=\frac{c}{f}$ and $f=\frac{c}{\lambda}$ where $\lambda$ is wavelength ($nm$) and $f$ is frequency ($Hz$) and $c$ is the speed of light (approx. 2.10⁸ m/s)

**As wavelength increases, frequency decreases.**
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When discussing Dense Wavelength Division Multiplexing (DWDM), frequency is preferred, in $THz$

==== Electromagnetic spectrum ====

{{network:light_spectrum-cropped.png?1500}}


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**Infra**-red and **Ultra**-violet are prefixed using **frequency** in mind : 

  *infrared has a lower frequency than the red in the visible spectrum (thus a higher wavelength)

  * ultraviolets have a higher frequency than the edge of our visible spectrum (thus a lower wavelength)
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==== Advantages over copper connections  ====

  ***Extremely wide system bandwith :** With LEDs (5 ns response time) the bandwith is limited to about 100 MHz but with a laser light source data rates of 10 Gbps are possible on a single-mode fiber. By multiplexing, one can reach hundreds of Gbps.

  ***Immune to electrostatic interference :** External electrical noise does not affect the data transmission in fiber optics. However, other metallic points (connections, components, etc.) may be affected.

  ***No crosstalk :** Contrary to copper cable, light in fiber optics do not interfere from one fiber to another even if they are very close to each other.

  ***Low signal attenuation :** Typical attenuation is about 0.03 dB per 100 feet.

  ***Cost competitive :** With massive deployment costs are dropping.

  ***No electricity involved** 

  ***No corrosion**

  ***Harder to intercept/tap**




Requires efficient optical connectors due to excessive loss that can occur at connection points.


==== To Do on this page ====
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Insert electromagnetic chart.

Link to wikipedia page on light spectrum.
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