Two optical splitters in a fiber distribution box are typically used in a cascaded configuration to efficiently distribute optical signals to multiple end users while managing signal loss.

Purpose of Two Splitters

In fiber optic networks, especially in Passive Optical Networks (PON) like GPON or FTTH, a single optical line from the central office (OLT) often needs to serve many users. Using two splitters in a cascaded setup allows the network to divide the optical signal in stages, reducing fiber usage and installation costs while maintaining signal quality . The configuration usually follows: OLT → Primary Splitter → Secondary Splitter → ONU/ONT .

How Cascaded Splitters Work

• Primary Splitter: Receives the optical signal from the OLT and splits it into several outputs, typically with a ratio of 1:4 or 1:8 .
• Secondary Splitter: Each output from the primary splitter is further divided, often with a ratio of 1:8 or 1:16, to reach individual subscribers . This two-stage splitting ensures that the optical power is distributed efficiently, minimizing insertion loss and allowing flexible network design for areas with dispersed user distribution, such as rural communities .

Types of Splitters

• PLC (Planar Lightwave Circuit) Splitters: Provide uniform splitting, support higher split ratios (up to 1:64), and operate over a wide wavelength range with stable performance .
• FBT (Fused Biconical Taper) Splitters: Made by fusing fibers together, suitable for lower split ratios (up to 1:32), and are cost-effective but more sensitive to temperature changes .

Deployment Considerations

• Centralized vs. Distributed Splitting: Centralized splitting places splitters in a single location, allowing easy reassignment of fibers, while distributed splitting uses smaller splitters along the route, often with fixed outputs .
• Signal Quality: Limiting to two stages of splitting helps maintain sufficient optical power at each subscriber's end and reduces network complexity .
• Flexibility: Cascaded splitters allow network designers to adjust splitting ratios based on user density and geographic distribution, optimizing fiber usage and reducing costs . In summary, having two optical splitters inside a fiber distribution box is a common practice in PON networks to achieve efficient, flexible, and cost-effective signal distribution while ensuring reliable service to multiple subscribers.