How to calculate fiber optic loss when designing the ODN

Our clients want to try the fiber network, so they bought the OLT, splitter and ONU.

Client A: Hello FOT, we connected the OLT, splitter, ONU in our lab to do testing, but they can’t work, why?

FOT: How do you connect them?

Client A: OLT PON port->1:4 PLC splitter->ONU.

FOT: Ok, please disconnect ONU first, or we are afraid the ONU will be burned ……

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Client B: Hi FOT, we have put the OLT and ONU in our network, but they can’t work, why?

FOT: How do you connect them?

Client B: OLT PON port->1:4 PLC splitter-1:8 PLC splitter->1:32 PLC splitter->ONU.

FOT: Why are there so many splitters?

Client B: Because we have many users nearby in the link ……

Though the PON network is passive in ODN, the OLT and ONU device are active, so we should consider the input/output power, loss when designing and deploying the fiber network. Here we would like to share a simple of fiber optic loss calculation so that our clients can avoid the mistakes of above examples.

Generally, the PON network connection is OLT->ODN (splitter, fiber cable, adapter, fast connector)->ONU.

The OLT PON SFP output power is 2~7dBm, ONU received sensitive is -27~-8dBm.

The PLC splitter loss:

Ratio1:21:41:81:161:321:64
Loss(dB)47.511141721
Ratio2:21:41:81:161:321:64
Loss(dB)4.4811.514.517.521.5

Fiber optical cable loss:

Wavelength(nm)Loss
1310≤0.36 dB/km
1490≤0.23 dB/km
1550≤0.25 dB/km

Connection point loss:

TypeLoss(dB)
SC fast connector≤0.5
Mechanical splicer≤0.2
Melt splicer≤0.1
SC adapter≤0.05

Now, let’s calculate the ONU rough input power of Client A and B.

Client A connection is OLT PON port->1:4 PLC splitter->ONU. Let take the OLT SFP output power as 4dBm, so the ONU input is 4-7.5=-3.5d. -3.5dBm>-8dBm, ONU received power is too high, that’s why can’t work!

How about the B client? 4-7.5-11-14=-28.5. -28.5dBm<-27dBm, the ONU received power is too lower, that’s why can’t work!

Well, the mentioned power and loss maybe not totally the same as the goods you are using. Get a power meter to measure it!

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