By goodvin | 06 July 2023 | 0 Comments
Fiber Optic Testing and Measurement Techniques
Fiber Optic Testing and Measurement Techniques
When installing and managing fiber optic networks, testing and measurement techniques are essential for ensuring proper network performance and troubleshooting issues. Several key fiber optic testing methods are commonly used.
1.Power Meter and Light Source Testing
The simplest yet most crucial fiber optic tests involve a light source and a power meter. A light source injects light into a fiber, while the power meter measures the power level of the light coming out of the fiber. This allows technicians to verify fiber continuity and end-to-end loss.
Technicians will perform an insertion loss test, where they measure the power injected by the light source and compare it to the light exiting the fiber and entering the power meter. Any difference in power indicates losses within the fiber due to factors like dirty connectors, bent fibers, or fiber breaks.
The results are compared to loss budgets and manufacturers' specifications to determine if the fiber meets requirements. Repeat tests can ensure connections and splices perform consistently over time.
2.Optical Time Domain Reflectometer (OTDR) Testing
An OTDR is an essential tool that uses light pulses to detect events along a fiber, like connectors, splices, and breaks. The OTDR measures the amount of light scattered or reflected back from these events.
The OTDR generates a graph showing the location of events and their reflection or loss. Technicians can determine the loss at any point as well as end-to-end. The high resolution of modern OTDRs enables detecting microbends and other subtle issues.
OTDR testing is done after fiber installation to characterize the link and establish a baseline. Repeating the test allows fiber managers to identify new events and degradation over time. OTDRs are critical in pre-installation site surveys and fiber tracing.
3.Bit Error Rate (BER) Testing
Once fibers are installed and commissioned, network engineers must ensure they can meet the bit error rate required by the network protocols and services running over them.
BER testers inject pseudo-random bit sequences into the fiber while a receiving unit monitors for errors. The ratio of erroneous bits to total bits transmitted yields the BER.
BER testing is performed during initial acceptance testing of fibers. Regular BER monitoring can detect degradation so issues can be addressed before bit errors affect network performance. BER tests are done for different wavelengths, data rates, and distances used in the network.
Conclusion
Fiber optic testing and measurement techniques ensure newly installed fibers perform as specified and detect faults before they impact network and system uptime. Regular testing verifies the fibers continue meeting standards and catches degradation early. A comprehensive testing program incorporating power metering, OTDR, and BER tests provides the visibility and data needed to proactively manage fiber plants.
FAQs
Q1: What other tests are performed on fiber optic networks?
• Visual Fault Locator (VFL) testing using laser light to detect broken fibers or lossy connectors
• Multimode Laser source and power meter testing to find faults in short-distance multimode fibers
• Optical Time Domain Reflectometry (ΦOTDR) for measuring pulse dispersion
• Polarization-mode dispersion (PMD) testing for high-speed networks
Q2: What factors affect fiber loss measurements?
• Dirty or damage connectors
• Bends or kinks in the fiber that exceed the minimum bend radius
• Microbends and compressions
• Cracks or breaks in the fiber
• Aging or environmental effects on the fiber and connectors
Q3: What are some causes of high bit error rates over fiber?
• Dirty or poorly installed connectors
• Bends or stresses on the fiber
• Fiber breaks or damage
• Exceeding the specified length for the data rate and wavelength
• Component failure within fiber transmission equipment
• Interference from other network equipment or crosstalk
Q4: How often should maintenance fiber optic testing be performed?
The frequency of maintenance testing depends on several factors, including the importance of the network, the reliability required, and environmental factors. As a rule of thumb, monthly OTDR testing and yearly BER testing is recommended for critical networks. Hospitals and data centers may perform testing quarterly or biannually, while less sensitive offices may test annually.
Q5: What is the typical decibel loss budget for fiber links?
Typical decibel loss budgets for new multimode fiber links range between 2 to 3 dB, while single-mode fibers have budgets between 8 to 10 dB. The loss budgets depend mainly in the fiber length and connections used.
KEYWORDS: fiber optic testing, OTDR, BER testing, light source and power meter, fiber optic network testing
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