OLT to Secondary Spectrum Splitter Attenuation Standard

Attenuation from an OLT to a secondary optical splitter depends on the splitter type, split ratio, and deployment architecture, typically ranging from 3–20 dB for cascaded PON splitters.

Understanding Attenuation in PON Splitters

In a Passive Optical Network (PON), the OLT (Optical Line Terminal) sends downstream signals to multiple ONTs via optical splitters. Each splitter introduces insertion loss, which is the reduction in optical power due to the splitting process. The amount of attenuation depends on:

• Split ratio: Higher split ratios (e.g., 1:32 or 1:64) divide the input power among more outputs, increasing insertion loss. For example, a 1:2 splitter typically has ~3.5 dB loss, while a 1:32 splitter can have ~17 dB loss .
• Splitter type: FBT (Fused Biconical Taper) splitters are cost-effective for small splits but may have slightly higher and temperature-sensitive losses. PLC (Planar Lightwave Circuit) splitters provide uniform and predictable loss, preferred for large splits .
• Cascaded deployment: When using a two-level splitter architecture (e.g., 1:4 primary splitter followed by 1:8 secondary splitter), the total attenuation is approximately the sum of the individual splitter losses plus fiber and connector losses. For instance, a 1:4 splitter (~7 dB) cascaded with a 1:8 splitter (~10 dB) results in ~17 dB total splitter loss .

Practical Considerations

• Distance and fiber loss: In addition to splitter loss, fiber attenuation (typically 0.35 dB/km at 1310 nm and 0.25 dB/km at 1550 nm) and connector/splice losses (~0.2–0.5 dB each) must be included in the power budget.
• Power budget planning: To ensure reliable service, the OLT's output power must exceed the total path loss to the ONT, including all splitters, fiber, and connectors.
• Uniformity: PLC splitters provide consistent output across all ports, which is important for maintaining balanced signal levels to multiple ONTs .

Summary

The attenuation from an OLT to a secondary splitter in a cascaded PON setup is the sum of the primary and secondary splitter losses, typically ranging from 10 dB for small splits to over 20 dB for high split ratios. Proper selection of splitter type, split ratio, and careful power budget calculation ensures sufficient optical signal reaches each ONT, maintaining network performance and reliability .