QUICKSTART GUIDE
QS.3.4 Maximum fiber segment length calculation:
The maximum fiber segment length between two adjacent switches or between a switch and a device is calculated in the following way:
First, calculate the optical power budget (OPB) of each device using the manufactures data sheets. Shown below are sample data sheets.
OPB = PT(min) - PR(min)
where:
OPB = Optical Power Budget PT = transmitter output power PR = receiver sensitivity
The worst case optical power budget (OPBWORST) is then calculated by taking the lower of the power budgets for the two devices, calculated above, and subtracting 1 dB for LED aging and then subtracting the total insertion loss. The total insertion loss is calculated by multiplying the number of connectors in each single fiber path by 0.5 dB. For example, with a single fiber cable between the two devices there would be a minimum of two connections in either transmit or receive fiber paths for a total insertion loss of 1db for either direction:
Total insertion loss = number of connectors x 0.5db Total insertion loss = 2 x 0.5 dB = 1.0 dB.
Example: Assuming 62.9/125μm cable
Speed | Mode | λ | Size | PT | PR |
100 Mb FX | multi | 1300 nm | 62.5/125 μm | ||
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If we were calculating the
OPBWORST = OPB - 1 dB (LED aging) - total insertion loss OPBWORST = 10 dB - 1 dB - 1 dB
OPBWORST = 8 dB
To calculate the maximum fiber length, divide the
Maximum fiber length = worst case OPB (in dB)/cable loss (in dB per km) Maximum fiber length = 8 dB/2.8 dB/km= 2.8 km
Again, the customer must use the attenuation specified within the manufacturer’s data sheets for accurate calculation of the maximum fiber length.
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