GE QS24 UR quick start QS.3.4 Maximum fiber segment length calculation

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

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 62.9/125μm cable

Speed	Mode	λ	Size	PT	PR
100 Mb FX	multi	1300 nm	62.5/125 μm	-20 to -23.5 dB	-31 dB
			50/125 μm		-31 dB

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:

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 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.

UR SWITCH MODULE – QUICKSTART GUIDE QS–11