OLT to Level 1 Optical Exchange Box Optical Attenuation

The typical optical attenuation from an OLT to a Level 1 Optical Exchange Box in a Class B FTTH network is up to 28 dB, measured using an Optical Loss Test Set (OLTS) or Light Source and Power Meter (LSPM).

Optical Attenuation Overview

Optical attenuation refers to the loss of optical power as light travels through fiber, connectors, and splitters between the OLT and the first distribution point, such as a Level 1 Optical Exchange Box (OEB) or Fiber Distribution Hub (FDH) in FTTH networks . This loss is influenced by:

• Fiber length (feeder fiber from OLT to OEB)
• Connector and splice losses
• Passive optical splitters (if present)
• Fiber type and quality In a typical Class B optical network, the maximum permissible optical power loss from the OLT to the ONT is 28 dB, which includes the attenuation through the Level 1 exchange box and any splitters . Class A, B, and C networks differ in optical budget, with Class B being commonly deployed for commercial 1:64 split ratios.

Measurement Methods

Optical attenuation is measured using:

1. Optical Loss Test Set (OLTS): Consists of an Optical Light Source (OLS) and an Optical Power Meter (OPM). The OLS injects a known optical signal into the fiber, and the OPM measures the received power at the Level 1 box. The difference gives the link loss .
2. Light Source and Power Meter (LSPM): Similar to OLTS, often used for Tier 1 testing, including link attenuation, link length, and polarity verification . Measurements are typically performed at the operating wavelengths of the network (e.g., 1310 nm upstream, 1490 nm downstream for GPON) and may be conducted bidirectionally to ensure accuracy.

Practical Considerations

• Ensure connectors are clean and properly mated to minimize insertion loss.
• Account for splitter losses: a 1:2 splitter introduces ~3.5 dB loss, 1:4 ~7 dB, and 1:8 ~10.5 dB.
• Maintain a sufficient optical budget to accommodate future network expansion or additional splices.
• Record baseline measurements during installation for future troubleshooting .

Summary

For a standard FTTH deployment, the OLT to Level 1 Optical Exchange Box attenuation should not exceed 28 dB in a Class B network. Using an OLTS or LSPM ensures accurate measurement of the optical link, including fiber, connectors, and splitters, providing a reliable baseline for network performance and maintenance . Proper testing and documentation are essential for maintaining signal quality and ensuring the network meets design specifications.