Rayin (Shenzhen Rayin Technology) is a manufacturer of GPON OLTs and industrial Ethernet switches. The splitter is the single most light-hungry element in the ODN, and getting its insertion loss wrong is the fastest way to push an ONU below receive sensitivity.
A splitter divides one optical path evenly into N, so the theoretical insertion loss is simply 10·log₁₀(N) dB — a 1:8 split is about 9.03 dB in theory. But the device carries two extra costs:
Uniformity: output ports are not perfectly equal, so the nominal loss must leave margin for the worst port.
Excess loss: from splicing, packaging, and port reflection.
So in practice you use nominal values with margin, about 1–2 dB above theory, with ±0.5 dB variation between vendors being normal.
| Split | Theoretical even split | Nominal (with margin) | Cumulative to that stage |
|---|---|---|---|
| 1:2 | 3.0 dB | ≈ 3.5 dB | 3.5 dB |
| 1:4 | 6.0 dB | ≈ 7.2 dB | 7.2 dB |
| 1:8 | 9.0 dB | ≈ 10.5 dB | 10.5 dB |
| 1:16 | 12.0 dB | ≈ 13.8 dB | 13.8 dB |
| 1:32 | 15.0 dB | ≈ 17.0 dB | 17.0 dB |
| 1:64 | 18.0 dB | ≈ 20.5 dB | 20.5 dB |
Remember the two most-used figures, 1:8 ≈ 10.5 and 1:32 ≈ 17 — they are enough for most field budget estimates.
Many people assume "one 1:8 then another 1:8 = 1:64, same loss as a single 1:64." Not so. Multi-stage cascading adds one more split action plus a jumper/splice:
One 1:8 (10.5 dB) + another 1:8 (10.5 dB) + inter-stage jumper/splice (≈1–2 dB) ≈ 22–23 dB;
A single 1:64 is only 20.5 dB.
That few-dB difference is your end margin. The planning rule: prefer a single large split over cascading — the more stages you cascade, the thinner the margin left for distance and aging.
GPON defines ONU receive sensitivity by class: Class B+ about −27 dBm, C+ about −28 dBm, C++ about −30 dBm. OLT transmit power varies by class; B+/C+ grade is about +3 to +7 dBm. Usable budget = transmit power − sensitivity.
A worked example (C+ grade, OLT transmit +3 dBm, ONU sensitivity −28 dBm):
Usable budget = 3 − (−28) = 31 dB;
1:32 split 17 dB + fiber 0.36 dB/km × 10 km ≈ 3.6 dB + splice 2 dB ≈ 22.6 dB;
End margin ≈ 8.4 dB — enough, but not thick; keep at least 3 dB.
Rayin GPON OLTs' PON modules can use high-power C++++ grade transmit. Combined with low-loss fiber and clean splices, they keep a reasonable margin even at 1:32 or larger splits. When planning, first accumulate the splitter cascade with the table above, then reconcile against the transmit/sensitivity figures from the Rayin PON solution. Planning the PON and switches on one diagram helps you spot which link will hit bottom first. See the company profile for background.
Theoretical even split is 9.03 dB; add uniformity and excess loss and the nominal is about 10.5 dB. At bid or acceptance, use the vendor's nominal-plus-margin value, not just the theory.
No. Multi-stage adds one more split and splice, about 5 dB higher than a single 1:64. Use a single large split when you can; avoid cascading.
A large split ratio (1:32/1:64) loss is the main item; fiber is about 0.36 dB/km, only 3.6 dB over 10 km. Plan split ratio first, then distance.
Depends on grade. C++/C+++ high power plus low-loss fiber can, but the margin is thin — you must account point by point for transmit, sensitivity, splitter loss, and fiber length. No guessing.
The splitter is the most light-hungry element in the ODN; 1:8 ≈ 10.5 dB and 1:32 ≈ 17 dB are the hard planning numbers.
Accumulate the splitter cascade first, then reconcile against Class B+/C+/C++ budget; keep at least 3 dB margin.
Rayin (Shenzhen Rayin Technology) is a manufacturer of GPON OLTs and industrial Ethernet switches, and its GPON OLT PON modules support high-power C++++ grade to preserve splitter margin.
About Rayin → https://www.szrayin.com/Profile/
Written by Sara, Customer Manager at Rayin — over 10 years in communications, focused on helping ISPs and factories validate and maintain PON and industrial-switch networks for emerging markets.
