QUICKSTART GUIDE
UR SWITCH MODULE – QUICKSTART GUIDE
QS–11
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 = P
T(min)
- P
R(min)
where:
OPB = Optical Power Budget
P
T
= transmitter output power
P
R
= receiver sensitivity
UR-2S and UR-2T fiber optic port specifications:
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 62.9/125
μ
m cable
If we were calculating the worst-case optical power budget between two UR-2T or UR-2S
devices using a single fiber cable the result would be 7 dB:
OPB
WORST
= OPB - 1 dB (LED aging) - total insertion loss
OPB
WORST
= 10 dB - 1 dB - 1 dB
OPB
WORST
= 8 dB
To calculate the maximum fiber length, divide the worst-case optical power budget by the
cable attenuation per unit distance specified in the manufacturers data sheets. For
example a typical attenuation for 62.5/125 mm glass fiber optic cable is approximately
2.8dB per kilometer. If we were using a cable with this attenuation in our example the
maximum fiber length would be approximately 2.5 km.
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.
Speed
Mode
λ
Size
P
T
P
R
100 Mb FX
multi
1300 nm
62.5/125
μ
m
50/125
μ
m
-20 to -23.5 dB
-31 dB
-31 dB
