Joining two buildings
A school has two buildings 400 metres apart. A copper cable cannot cross that gap, and a storm near the link would fill it with noise.
A fibre cable can cross it with ease and ignores the storm. This lesson looks at what fibre is good at, where it is used and the grades you must know.
Key words
| Word | What it means |
|---|---|
| Single mode | fibre with a thin core and one path of light |
| Multi-mode | fibre with a wide core and many paths of light |
| OS1 and OS2 | grades of single mode fibre, OS2 being the better |
| OM3 and OM4 | grades of multi-mode fibre made for lasers, OM4 reaching further |
| Bandwidth | how much data a link can carry each second |
| Channel capacity | how many signals one cable can carry at once |
| Degradation | the damage a signal suffers on the way |
| Laser | a light source that makes a narrow, strong beam |
| Interconnect | join two places so they can pass data |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can give the features and uses of fibre, and name the grades OS1, OS2, OM3 and OM4.
Starter: single mode and multi-mode
Have a go
Starter: single mode and multi-mode
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Why use fibre
Fibre goes far. It has very high bandwidth and high channel capacity, so one thin cable can carry a great deal. It is light, which makes a long pull easier. Its signal suffers less degradation. The glass is cheap to make.
One limit: the link can only go as far as the laser at each end allows. Good light sources cost more.
Where fibre is used
Fibre carries large data rates. It interconnects buildings on a campus. It serves long links between sites, towns and countries.
In a single building it is used for the main cables between floors, and for kit that needs a very fast link, such as servers.
The four grades
| Grade | Type | Core and path | Reach, roughly | Jacket colour |
|---|---|---|---|---|
| OS1 | Single mode | About 9 micrometres, one ray | Many kilometres. Indoor use | Yellow |
| OS2 | Single mode | About 9 micrometres, one ray | Many kilometres. Lower loss, often outdoor | Yellow |
| OM3 | Multi-mode | About 50 micrometres, many rays | About 300 metres at 10 Gbit/s | Aqua |
| OM4 | Multi-mode | About 50 micrometres, many rays | About 400 metres at 10 Gbit/s | Aqua, sometimes violet |
The cells students fill in are left blank in this preview.