When we talk about the methods of testing splice loss, many people would take OTDR (Optical Time Domain Reflectometer) as the best fiber optic equipment to test splice loss. But instead, OTDR is not specifically used to test splice loss. If you use OTDR to test, the measured splice loss standard will be inaccurate. So in this article, we will talk about what is splice loss in optical fiber and how to test splice loss.
What is splice loss in optical fiber?
Fiber splice loss refers to the amount of optical signal lost at the point where two fibers are joined. Accurate measurement of splice loss is critical for ensuring network performance, reliability, and compliance with industry standards. This guide explains the most reliable methods of testing splice loss, highlights common mistakes, and shares professional tips to help you achieve low‑loss splices.
3 Methods for Testing Splice Loss
1. OTDR Testing (The Most Common Method)
An Optical Time-Domain Reflectometer (OTDR) is the industry-standard tool for splice loss testing. It works by sending a pulse of light down the fiber and analyzing the backscattered light to create a trace, or signature, of the entire link. Splices appear as distinct “loss events” on this trace.
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How it works: The OTDR calculates loss by comparing the backscatter levels before and after the splice point.
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Advantages: Provides a visual map of the entire fiber link, can measure loss of individual splices, and can find the location of faults.
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Disadvantages: Requires expertise to interpret traces accurately and can yield different results depending on the direction of the test (hence the need for bidirectional averaging).
Pro Tip: Always perform bidirectional OTDR testing and average the results for the most accurate splice loss measurement. This cancels out inherent measurement errors.
2. Source and Power Meter (OLTS) Testing
This method uses a stable light source (LS) at one end of the fiber and a optical power meter (OPM) at the other. The loss is measured directly by comparing the power transmitted into the fiber to the power received at the end.
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How it works: The loss measured is the total end-to-end loss of the link, including all splices and connectors. To isolate a single splice’s loss, you must measure the total loss with and without the splice—a process often impractical after the fact.
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Best for: Certifying the total loss of a complete fiber link (a requirement for many standards), rather than measuring individual splices.
3. Local Injection and Detection (Built-in Splicer Testing)
Most modern fusion splicers have a built-in function called Local Injection and Detection (LID) or an equivalent real-time loss estimation feature.
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How it works: The splicer uses its own light source and detector to make a local attenuation measurement across the splice point immediately after the arc fusion process.
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Advantages: Provides an instant estimate of splice quality.
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Disadvantages: This is an estimation, not a substitute for a true end-to-end test with an OTDR or OLTS. It doesn’t account for macro/micro bends that may be introduced when placing the splice into a tray.
Why OTDR is not specifically used to test splice loss?
Firstly, after a fiber is fused, if it is a long distance fiber, the splice loss will be too low for the OTDR to detect on the splice point. Secondly, even if there is a high loss point detected on the fiber, it may be caused by error operation, that is to say the fiber is not spliced correctly. After calibrating the arc, you can clean the fiber and re-splice the fiber.
OTDR 3000 testing
Step‑by‑Step: How to Measure Fiber Splice Loss
1. Take out a length of optical fiber.
2. Use a Light Source on one side, and an Optical Power Meter on the other side, to measure the loss of this fiber.
3. Cut the optical fiber into two pieces
4. Use Fiber Fusion Splicer to splice the two pieces of the optical fiber.
BD-FS-41B Optical Fiber Fusion Splicer
5. After splicing, use Light Source and Optical Power Meter to measure the fiber loss again.
After Splicing
- The subtraction of the two fiber loss values will be the real splice loss of the fiber.
Note:
- You should use high precision Light Source and high precision Optical Power Meter, or the value would be inaccurate.
- You should keep the output power of Optical Light Source stable and in the same value.
Frequently Asked Questions (FAQ)
Q: What is an acceptable splice loss?
A: The industry standard for a well-executed fusion splice is < 0.10 dB for single-mode fiber and < 0.30 dB for multimode fiber. However, project specifications often demand even lower values, such as < 0.05 dB. Always consult your project’s design documents for the required standard.
Q: Why is bidirectional OTDR testing necessary?
A: Fiber attenuation and backscatter coefficients are not perfectly uniform. A splice can measure different loss values from opposite directions. Bidirectional testing averages the loss from both ends, providing a true, accurate measurement that complies with IEC standards.
Q: What causes high splice loss?
A: Common causes include fiber core misalignment (lateral offset), angular misalignment, contaminated fiber end faces, air gaps (in mechanical splices), and core diameter mismatches between different fibers. A high loss reading indicates the splice should be re-cleaved and re-spliced.
Conclusion
Testing splice loss ensures the long‑term reliability and efficiency of fiber optic networks. While OTDRs are useful, the most accurate method for measuring splice loss is with a light source and power meter. By following industry standards, using the right tools, and applying best practices, you can achieve high‑quality, low‑loss fiber optic splices.
Baudcom offers all types of fiber optic test equipment and fusion splicers. For more information, please feel free to contact us.
【Edited in September 2025】
