Data rate and fiber optic cable length. |
Document: 10035
Category: General Information
Date Posted: 03/15/03 |
Problem
Is data rate a function of fiber optic cable length?
Solution
Fiber optic cable has bandwidth limitations, normally specified as MHz/km. For example:
| 62.5/125 multimode fiber |
200 MHz/km @ 850 nm |
| |
500 MHz/km @ 1300 nm |
| 50/125 multimode fiber |
600 MHz/km @ 850 nm |
| 8.5/125 single mode fiber |
Several GHz/km @ 1300 nm or 1550 nm |
To determine maximum distance your data can travel, divide bandwidth by data rate. For example:
62.5/125 fiber - 200 MHz/km @ 850 nm / 20 Mbps = 10 km max
Besides bandwidth, you need to consider attenuation (loss) normally express as dB/km @ a given wavelength (850/1300/1550)
62.5/125 fiber - 3.5 dB/km @ 850 nm
Therefore, for 10 km, you will have 35 dB loss which is beyond power budget of most fiber optic transmitter/receivers.
So practically, 5 km or 20 dB is maximum limit.
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