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Why Must Fiber Optic Cable Acceptance Testing Be Performed? What Should Be Tested?

Acceptance testing is conducted based on engineering design or contractual specifications to test various indicators of optical transmission characteristics of fiber optic cables during project acceptance. Acceptance testing includes line attenuation testing and backscatter signal curve testing. These tests help prevent unexpected problems in subsequent engineering work.

In the acceptance of fiber optic cable projects, in addition to testing fiber optic cable transmission characteristic indicators, special attention should be paid to the installation workmanship of cable routes and station terminal sections. For concealed parts of the project, random inspection methods should be adopted for verification, and key locations must be documented through photographs and other means, with detailed records maintained. The following will mainly introduce the acceptance optical performance testing procedures and requirements for power communication fiber optic cable projects.

Fiber Optic Cable Line Attenuation Testing

During fiber optic cable line acceptance, line attenuation testing must be performed on all fibers in the cable. Bidirectional testing should be conducted from both end stations using test wavelengths of 1310nm and 1550nm. Understanding how to test fiber optic cable properly is essential for accurate results. The testing steps are as follows:

(a)Test both end stations to verify that instruments function normally and test pigtails are in good condition. Ensure all fiber optic cable testing equipment is calibrated and ready for use.

(b)One end station uses a light source for transmission. First, connect the light source directly to the optical power meter through the test pigtail. The optical power meter is generally set to continuous wave (CW) state with wavelengths of 1310nm and 1550nm to measure the transmitting end optical power.

(c)The transmitting end connects the light source to the fiber under test through the test pigtail. Before testing fiber optic cable connections, the fiber connection points should be cleaned using a fiber optic cable cleaner. 

(d)Connect the same numbered fiber core at the receiving end to the optical power meter. Clean the fiber connection points before testing. After the reading stabilizes, subtract the transmitting end optical power from the measured optical power to obtain the unidirectional line attenuation value.

(e)Repeat the above steps to measure other fiber cores. After completion, swap the transmitting and receiving ends at both stations and measure again.

Use a recording form to document fiber attenuation test results. If testing reveals issues such as misaligned fiber sequences between stations, excessive fiber core attenuation, or broken cores, the fiber optic cable cannot pass acceptance for commissioning. The construction unit must be notified immediately to investigate problems and complete corrections.

Complete Fiber Optic Cable Backscatter Signal Curve Testing

During completion acceptance, OTDR (Optical Time Domain Reflectometer) testing should be performed on each fiber core to test backscatter curves. The OTDR is an essential fiber optic cable tester that provides comprehensive analysis of fiber characteristics. The curve attenuation characteristics can be used to observe the fusion splicing quality of fiber optic cable line joints, determine whether fiber fusion splice points are reliable and if there are any abnormalities, whether fiber attenuation distribution is uniform, and if there are any damages, steps, or other abnormal phenomena along the entire fiber length.

When learning how to test a fiber optic cable with an OTDR, the testing operation steps are as follows:

① Clean the test fiber connector using a fiber optic cable cleaner and connect the OTDR to the fiber core under test. A fiber optic cable launch cable may be used at the beginning of the test fiber to eliminate the OTDR's dead zone and provide accurate measurements of the first connection point.

② Parameter settings:

a. Fiber parameters: Refractive index and backscatter coefficient parameters should be set according to data provided by the fiber manufacturer. The more accurate the settings, the higher the measurement precision.

b. Wavelength selection: 1310nm and 1550nm.

c. Pulse width selection:

Lines under 5km typically select 50ns

Lines under 10km typically select 100ns

Lines around 40km typically select 300ns

Lines of 50-80km typically select 500ns

Lines over 80km typically select 1000ns

On-site operations can be adjusted according to actual line conditions.

d. Range selection: Generally set to 1.5-2 times the length of the fiber under test.

e. Averaging time: Longer averaging time reduces the impact of inherent random measurement noise and increases signal-to-noise ratio. Selection is typically based on actual line length.

③ Begin testing.

④ Save and analyze test curve results.

Testing should be completed at both end stations of the fiber optic cable using appropriate fiber optic cable testers. Test results graphs for each fiber core should be saved, and testing should be recorded using Table. Professional fiber optic cable testing requires systematic documentation of all measurements.

For lines exceeding 150km, the length may exceed the OTDR's dynamic range. In this case, measurements can be taken from both end stations separately, with a reference point selected at approximately 1/2 of the total cable length for analysis, and the results combined to obtain total cable length and line loss information.

Additional Testing Considerations

When performing fiber optic cable testing, technicians should also be familiar with using a fiber optic cable checker for quick continuity verification and a fiber optic cable loopback cable for testing transceiver functionality at equipment interfaces. Understanding how to check fiber optic cable integrity using various tools ensures comprehensive quality assurance throughout the acceptance process.

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