Optimizing LCLC Patch Cords for Precise Fiber Testing

Imagine this frustrating scenario: after spending hours carefully splicing fiber optic cables and eagerly running tests, you're confronted with negative readings. These perplexing negative loss values and inconsistent results often stem not from the fiber itself, but from improper reference settings. While cleaning and inspecting fiber end faces is essential, it's only part of the solution. The critical step lies in verifying the performance of your reference patch cords.

In fiber optic testing, reference cables serve as the vital bridge between test equipment and the fiber link being measured. Their performance directly impacts the accuracy of test results. Defects such as end-face contamination, connector damage, or excessive fiber bending can lead to measurement deviations and even those frustrating negative loss readings.

The International Electrotechnical Commission (IEC) establishes clear standards in IEC 14763-3: reference connections for multimode fiber must not exceed 0.1 dB loss, while single-mode connections must stay below 0.2 dB. These benchmarks provide essential criteria for validating reference cable performance.

A common misconception suggests that factory-new cables need no verification. However, even pristine cables can suffer contamination or damage during production, shipping, or storage. Furthermore, manufacturing quality varies significantly between suppliers, with some cables failing to meet reference standards from the outset. Comprehensive validation of all cables—including new ones—remains essential for accurate testing.

Follow this detailed procedure using Fluke Networks' SimpliFiber Pro light source and power meter to validate LC-LC reference cables:

1. 1. Cleaning and Inspection:

   Thoroughly clean all test cable end-faces using high-purity (≥98%) isopropyl alcohol (IPA) and lint-free wipes. Specialized fiber optic cleaning kits provide optimal results. Subsequently, inspect each end-face for scratches, cracks, or contamination using a fiber inspection microscope. Replace any defective cables immediately.

2. 2. Equipment Startup and Stabilization:

   Power on the SimpliFiber Pro light source and engage automatic mode by pressing the "AUTO" button. This enables simultaneous dual-wavelength measurement. Allow the light source to stabilize for at least five minutes (longer if stored below 20°C/68°F) to ensure measurement accuracy.

3. 3. Reference Connection Setup:

   Connect the light source to the power meter as illustrated. When testing 850/1300 nm wavelengths, always use the appropriate color-coded mandrel: gray for 62.5/125 µm fiber, red for 50/125 µm fiber. These mandrels eliminate modal power distribution effects.

   Select "LOSS" mode and press "F3" to establish the reference baseline. A displayed "OK" confirms successful reference setting for both wavelengths.

4. 4. Reference Value Verification:

   With proper stabilization, the display should show 0.00 dB. Reference power levels should measure better than -20.00 dBm for 62.5/125 µm fiber, -24.50 dBm for 50/125 µm fiber, and -10.00 dBm for 9/125 µm fiber. Note that values closer to zero indicate better performance (e.g., -24.00 dBm outperforms -24.50 dBm).

5. 5. Connecting Test Cables:

   Disconnect from the power meter's "INPUT ONLY" port and insert the test reference cable into the "INPUT" port.

6. 6. Adapter Connection:

   Use a single-mode grade LC-LC adapter to connect both cables.

7. 7. Bidirectional Testing:

   Reverse the test cable connected to the "INPUT" port and repeat measurements. Single-direction testing cannot fully validate cable performance.

8. 8. Compliance Assessment:

   Cables meeting IEC 14763-3 standards will show losses below 0.1 dB for multimode or 0.2 dB for single-mode fibers. These validated cables become reliable references for subsequent fiber link testing.

While commercially available cables often specify ≤0.3 dB loss, these may negatively impact test accuracy. Premium reference cables meeting IEC 14763-3 requirements deliver superior measurement reliability.

Implement these protocols to maintain reference cable integrity:

• Assign unique identifiers to track usage history and performance
• Schedule regular cleaning, inspection, and validation with documentation
• Promptly repair or replace non-compliant cables
• Store cables properly to prevent bending, crushing, or contamination

Through rigorous reference cable validation and proper maintenance, technicians can eliminate negative loss readings, ensure measurement accuracy, and deliver reliable fiber network performance assessments.