How to test the loss of an optical fiber splice closure

The most reliable way to test splice loss is using an OTDR for diagnostic mapping and an optical loss test set (OLTS) for absolute insertion loss measurement.

Step 1: Understand the Testing Methods

There are two primary methods to test splice loss:

1. OTDR Testing (Tier 2): An Optical Time-Domain Reflectometer sends pulses of light through the fiber and measures backscattered light to create a trace of the entire link. Each splice appears as a distinct loss event, allowing you to locate and quantify the loss at individual splices. Bidirectional testing is recommended, averaging results from both directions to reduce measurement errors caused by fiber geometry or launch conditions .
2. OLTS / Source and Power Meter Testing (Tier 1): A calibrated light source is placed at one end of the fiber and a power meter at the other. This measures the total end-to-end insertion loss, including all splices, connectors, and fiber attenuation. This method provides the absolute loss value required for certification and compliance with standards like TIA-568.3-D .

Step 2: Prepare the Fiber and Equipment

• Ensure all connectors, launch cords, and adapters are clean and defect-free .
• Use reference-grade launch cables that match the fiber type to stabilize the OTDR launch and make the first splice visible in the trace .
• Select the testing wavelength(s) that match the network operation (e.g., 1310 nm or 1550 nm for singlemode fiber), .

Step 3: Perform OTDR Testing

• Connect the OTDR to the fiber using a launch cable.
• Shoot a trace from one end, then repeat from the opposite end for bidirectional averaging.
• Identify each splice on the trace and record the loss values.
• Compare the measured loss to the expected loss budget (typically 0.15 dB per singlemode fusion splice, 0.3 dB for multimode mechanical splices), .

Step 4: Perform OLTS Testing

• Connect the light source and power meter at opposite ends of the fiber.
• Measure the total insertion loss.
• If necessary, segment the fiber to isolate individual splice losses by measuring with and without specific sections, though this is often impractical after installation .

Step 5: Compare to Loss Budget

• Calculate the expected loss budget for the fiber plant, including fiber attenuation, splice loss, and connector loss .
• Typical singlemode fiber loss: 0.5 dB/km at 1310 nm, 0.4 dB/km at 1550 nm.
• Ensure measured losses do not exceed the calculated budget; otherwise, investigate high-loss splices for re-splicing or cleaning .

Step 6: Document Results

• Record OTDR traces and OLTS measurements for each splice closure.
• Include bidirectional OTDR averages and total insertion loss for certification purposes.
• Maintain documentation for network maintenance and troubleshooting.

Step 7: Follow Standards and Best Practices

• Adhere to TIA-568.3-D or project-specific specifications.
• Use both OTDR and OLTS testing for a complete assessment: OTDR for diagnostics and OLTS for absolute loss certification .
• Keep splice loss below recommended thresholds (0.15 dB average for singlemode fusion splices) to preserve link budget, especially in PON networks . By combining OTDR diagnostics with OLTS measurements and comparing results to a calculated loss budget, you can accurately test and verify the optical loss of a fiber splice closure, ensuring reliable network performance.