Free professional tool for ISP engineers and FTTH network designers. Instantly compute insertion loss, power at each subscriber port, and fade margin for PLC and FBT splitters — including dual cascade configurations. Covers GPON (1490 nm / 1310 nm), EPON, and RF video overlay (1550 nm). Also useful as an optical power budget calculator, FTTH link budget tool, and PLC splitter loss calculator.
| Parameter | Value | Unit | Description |
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Two-stage splitting is the standard architecture in large-scale FTTH deployments. A primary splitter serves distribution cabinets; a secondary splitter serves individual subscriber clusters. The table below shows real-world configurations with their total effective split ratios.
| Type | Primary | Port 1 Cascade | Port 2 Cascade | Total Split | Use Case |
|---|---|---|---|---|---|
| PLC | 1:2 | 1:4 (50%) | 1:8 (50%) | 1:8 / 1:16 | Business / Residential mix |
| PLC | 1:2 | 1:8 (50%) | 1:16 (50%) | 1:16 / 1:32 | Different density zones |
| PLC | 1:4 | 1:8 (each) | 1:8 (each) | 1:32 uniform | Standard FTTH — most common |
| FBT | 25:75 | 1:4 (25%) | 1:8 (75%) | 1:16 / 1:64 | Premium / Standard tier mix |
| FBT | 50:50 | 1:8 (50%) | 1:32 (50%) | 1:16 / 1:64 | Business + high-density residential |
The optical power budget determines whether your OLT can reliably serve every ONT on a given PON port. Follow these steps to plan your GPON link budget or FTTH fiber splitter network.
PLC (Planar Lightwave Circuit) splitters use semiconductor waveguide technology and provide uniform insertion loss across all output ports, regardless of the number of splits. They support the full wavelength range (1260–1650 nm) and are the standard choice for GPON, XGS-PON, and EPON networks. FBT (Fused Biconical Taper) splitters are made by physically fusing optical fibers together and allow asymmetric split ratios (e.g. 25:75 or 10:90), which is useful when different service zones need different power levels. PLC is preferred for most modern FTTH deployments due to wavelength independence and consistent performance across temperature ranges.
The ITU-T G.984 standard supports up to 128 logical subscriber ports per PON port. In practice, most FTTH deployments use 1:32 or 1:64 due to optical power budget constraints. A 1:32 PLC splitter introduces approximately 15.5 dB of insertion loss. With a Class C+ OLT (32 dB power budget) and a short fiber run, this leaves adequate margin for a reliable connection. A 1:64 split (~18.5 dB) requires careful planning and may need a higher-class OLT SFP module, especially for runs over 10 km.
For GPON (ITU-T G.984.2), ONT receive sensitivity ranges from −8 dBm (overload threshold) to −28 dBm (minimum sensitivity). The ideal received power is between −15 dBm and −25 dBm. Levels between −25 and −28 dBm are considered marginal and may cause intermittent errors during connector aging or temperature extremes. Below −28 dBm, the ONT will not register on the PON. Always design your network with a minimum 3 dB fade margin below your link budget threshold to ensure long-term reliability.
Yes. Dual cascade (two-stage splitting) is the standard approach in large-scale FTTH deployments. A typical design places a 1:4 splitter at the street cabinet or central office, and a 1:8 splitter at the building or neighborhood distribution point — giving a total effective split of 1:32 while allowing flexible network topology. This calculator supports dual cascade for both PLC and FBT splitters and calculates power at each stage independently. Enable the Dual Cascade toggle to configure different secondary ratios for each port.
Single-mode fiber (ITU-T G.652D) attenuates optical signals at approximately 0.35 dB per kilometer at 1310 nm (GPON upstream), 0.25 dB/km at 1490 nm (GPON downstream), and 0.20 dB/km at 1550 nm (RF video). A 10 km fiber run contributes 3.5 dB of loss at GPON upstream wavelengths. This calculator applies the correct attenuation coefficient for your selected wavelength automatically. For very long runs (over 20 km) combined with high split ratios, you may need a Class C++ OLT SFP module or an EDFA optical amplifier.
PLC dual cascade splits power equally (50/50) at the primary stage since PLC splitters always distribute uniformly. Each output port then feeds an independently configured secondary splitter. FBT dual cascade allows unequal primary splitting — for example, 25% to Port 1 and 75% to Port 2 — which is valuable when two service zones have different subscriber densities or service tiers. FBT gives more control over power distribution across zones but requires careful wavelength and temperature management for outdoor deployments.
With PLC dual cascade, a 1:2 primary plus 1:64 secondary yields a maximum effective split of 1:128. In practice, GPON protocol supports up to 128 logical ONUs per PON port (ITU-T G.984). However, total link loss is the real constraint. A 1:64 primary (18.5 dB) plus a 1:2 secondary (3 dB) plus a 5 km fiber run (1.75 dB at 1490 nm) already uses 23.25 dB of a 28 dB Class B+ budget — leaving only 4.75 dB for connectors, splices, and excess loss. Always verify total loss stays within your OLT power class before deployment.