Splitter loss table
A splitter divides the light, so each output gets a fraction of it: half for a 1×2, a thirty-second for a 1×32. In decibels the ideal loss is 10 log10(N), about 3 dB for every doubling. Real PLC splitters lose a little more than that, from excess loss and uniformity across the ports.
| Split | Ideal | Typical | Max |
|---|---|---|---|
| 1×2 | 3.01 | 3.6 | 4.0 |
| 1×4 | 6.02 | 7.0 | 7.3 |
| 1×8 | 9.03 | 10.2 | 10.5 |
| 1×16 | 12.04 | 13.5 | 13.7 |
| 1×32 | 15.05 | 16.5 | 16.9 |
| 1×64 | 18.06 | 20.5 | 21.0 |
Splitter values vary by about half a dB between vendors and grades, and some datasheets include the connectors. Use the datasheet for the part you are installing when you have it.
| Split | Max |
|---|---|
| 2×4 | 7.5–8.0 |
| 2×8 | 10.8–11.0 |
| 2×16 | 14.1–14.6 |
| 2×32 | 17.4–17.9 |
| 2×64 | 21.0–21.3 |
Cascaded splitters
Two splitter stages add their losses. A 1×4 in a cabinet feeding 1×8s in terminals gives the same 1:32 split as a single 1×32, with about the same total loss: 7.0 + 10.2 = 17.2 dB typical, against 16.5 dB for one 1×32. The extra connectors at the second stage are what usually make a cascaded design a little worse.
Worked example
GPON class B+, a 1×4 then a 1×8 (1:32), 10 km of fiber at 0.35 dB/km, four connector pairs at 0.5 dB, eight splices at 0.1 dB and a 3 dB margin.
- Splitters: 7.0 + 10.2 = 17.2 dB
- Fiber: 10 × 0.35 = 3.5 dB
- Connectors and splices: 2.0 + 0.8 = 2.8 dB
The ODN loses 23.5 dB, or 26.5 dB with margin, inside B+'s 13–28 dB range with 1.5 dB to spare. Using maximum splitter values instead (7.3 + 10.5) adds 0.6 dB and still fits.
PON optics classes
Each class of OLT and ONT optics is specified to work across a range of ODN loss. Too much loss and the ONT cannot hear the OLT; too little and a nearby ONT can be overloaded, which is why every class has a minimum as well as a maximum.
| Class | Min (dB) | Max (dB) |
|---|---|---|
| GPON class B+ | 13 | 28 |
| GPON class C+ | 17 | 32 |
| XGS-PON N1 | 14 | 29 |
| XGS-PON N2 | 16 | 31 |
| XGS-PON E1 | 18 | 33 |
| XGS-PON E2 | 20 | 35 |
GPON classes B+ and C+ are set in ITU-T G.984.2; XGS-PON classes N1 to E2 in ITU-T G.9807.1. Most GPON deployments use B+ optics. C+ costs more and buys about 4 dB, which can mean a bigger split or a longer reach.
Testing a PON
- Measure with a PON power meter at the ONT location; a standard meter cannot separate the downstream wavelengths.
- Use APC connectors throughout. PON carries video and high-speed data where reflections matter. See APC vs UPC.
- Test the feeder and each distribution leg before splicing in the splitters, so a bad splice is found while it is still cheap.