As already we have discussed in our earlier posts that there are different types of losses that are involved in the PON FTTH network so when we are building the FTTx network we should calculate the optical power on paper first and then we should deploy the fiber on the ground.
As we know the optical RX power of a ONU must be between -10 to -28 dBm . This power is the most optimal power of an ONU in the PON network and also we need to maintain this optical power amongst all ONUs in the PON port.
Find the types of losses given below.
- Splitter Loss.
- SFP Insertion Loss.
- Connector Loss.
- Splicing Loss.
- Fiber Distance Loss.
These are 5 losses but we take into account only 4 types of losses (Splitter, Connector, Splicing, and Fiber distance loss).
Sfp insertion loss is not required to include in the total loss calculation but make sure your sfp is installed properly and there is no loss at all.
There is another thing called safety margin loss, Safety Margin loss is that we need to keep reserved for 1-3 dBm for future loss adjustment .because in fiber optic, there are lots of chances of fiber bend and stretching so it’s best practice to keep in reserve for 1-3dBm power for future loss adjustment. So the calculation formula is given below.
Power Budget Formula.
Connector Loss + Splitter Loss + Splicing Loss + Fiber Distance Loss + Safety margin Loss – TX Power of the OLT POn Port = Total Optical Power Loss(RX Power Of ONU).
Example of Calculation.
Now let’s calculate the total loss of a given ONU below.
Let’s write down all losses first.
- The total distance from OLt to ONU is 8km so the loss would 8 * 0.4 = 3.2dBm.
- Total Connector is 4(Red Color Marked) so the total loss would be 4 * 0.7dBm=2.8dBm.
- Total Splitter is 3 pcs(1:4:,1:8,1:2) so the total loss would be 6.02 dbm + 9.03dBm + 3.01 dBm=18.06dBm.
- Let’s say the Total Splicing is 6 so the total loss would be 6 * 0.2 = 1.2 dBm.
The total power would be 1.6 + 2.8 + 18 + 1.2=23.6dBm + Safety Mragin 3 dBm = 26.6dBm
The Final power would be = TX power of OLT – Total power of loss , let’s say my TX power of OLT is 6 dBm .
Total RX power of Onu Would Be = 6dBm – 26.6 dBm = -20.6 dBm .
The splitter Loss Table is Given below.
Example -2
Let’s write down all losses first.
- The total distance from OLt to ONU is 8km so the loss would be 8 * 0.4 = 3.2dBm.
- Total Connector is 4(Red Color Marked) so the total loss would be 3 * 0.7dBm=2.1dBm.
- Total Splitter is 3 pcs(1:8:,1:16) so the total loss would be 9.03dBm + 12.04 dBm=21.07dBm.
- Let’s say Total Splicing is 5 so the total loss would be 5 * 0.2 = 1 dBm.
The total power would be 3.2 + 2.1 + 21.07 + 1 =27.37dBm + Safety Mragin 3 dBm = 30.37dBm
The Final power would be = TX power of OLT – Total power of loss, let’s say my TX power of OLT is 7 dBm .