Upstream and downstream equipment for optical splitters

Optical splitters connect upstream Optical Line Terminals (OLT) to multiple downstream Optical Network Terminals (ONTs) or Optical Network Units (ONUs), distributing downstream signals and aggregating upstream traffic in PON networks.

Upstream Equipment

The upstream side of an optical splitter is typically connected to an Optical Line Terminal (OLT), which is located in a central office or data center. The OLT serves as the network's aggregation point, converting electrical signals into optical signals for transmission over fiber. It manages both downstream broadcast traffic and upstream burst-mode traffic from multiple subscribers, often using Wavelength-Division Multiplexing (WDM) to separate upstream (1290–1330 nm) and downstream (1480–1500 nm) wavelengths . The OLT also handles time-division multiple access (TDMA) for upstream signals to prevent collisions .

Downstream Equipment

On the downstream side, the optical splitter connects to multiple Optical Network Terminals (ONTs) or Optical Network Units (ONUs) at the subscriber premises. These devices convert optical signals back into electrical signals for end-user devices such as computers, phones, or Wi-Fi routers . The splitter allows a single OLT port to serve multiple ONTs, with typical split ratios ranging from 1:2 up to 1:64 depending on network design and bandwidth requirements . Downstream signals are broadcast to all ONTs, while upstream signals are aggregated and sent back to the OLT through the same splitter.

Splitter Characteristics and Placement

Optical splitters are passive devices, requiring no power or active electronics, which reduces operational costs and increases reliability . They can be FBT (Fused Biconical Taper) for small splits or PLC (Planar Lightwave Circuit) for larger splits . Splitters are typically installed in distribution points, such as corridor boxes, cabinets, or rack-mounted 1U boxes, depending on network scale and deployment strategy . The optical power loss introduced by the splitter must be considered in the network power budget, as each split reduces signal strength by approximately 3.5 dB per 1:2 split .

Summary

• Upstream: OLT, responsible for signal aggregation, WDM, and TDMA management.
• Downstream: ONTs/ONUs, converting optical signals to electrical signals for end users.
• Splitter: Passive device distributing downstream signals and aggregating upstream signals, with placement in cabinets or racks and split ratios tailored to network design. This configuration ensures cost-efficient, scalable, and reliable fiber-to-the-home or fiber-to-the-building deployments.