This is an old revision of the document!
Fiber Optics
General information
The speed of light in free space is $c = 3.10⁸ (m/s)$
Fiber optics propagate light using the 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.
In fiber-optics, spectrum notation is generally stated in wavelength ($nm$) over frequency ($Hz$) because it is easier to use.
$\lambda=\frac{c}{f}$ 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.
When discussing Dense Wavelength Division Multiplexing (DWDM), frequency is preferred, in $THz$
Electromagnetic spectrum
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)
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
Insert electromagnetic chart.
Give both spectrums and highlight the relation between nm and Hz. As wavelength goes up, frequencies go down, etc.
Link to wikipedia page on light spectrum.