This article is about Fiber Optical Cable Testing and three methods Visible Light Source Testing, Power-Meter-and-Light-Source Testing, Optical Time Domain Reflectometer (OTDR) Testing.
Fiber Optical Cable Testing
Proper testing of Optical Fiber Cable is essential to ensure the efficient functioning of the system. Fiber optic cable is tested for continuity and attenuation to increase the system’s longevity, minimize system downtime, reduce maintenance needs, and support system upgrades and reconfigurations. In this article, we will discuss the importance of Optical Fiber Cable testing and the three commonly performed test methods.
Importance of Optical Fiber Cable Testing Optical Fiber Cable is widely used for transmitting data, voice, and video signals over long distances. However, environmental factors and physical stress can cause damage to the fiber optic cable, resulting in attenuation, signal loss, and downtime. Regular testing of Optical Fiber Cable can identify faults and defects, enabling timely repairs and preventing potential system failures.
Test Methods for Fiber Optical Cable
Three test methods are commonly performed for Optical Fiber Cable:
- Visible Light Source
- Power-meter-and light-source (One Jumper Method)
- Optical Time Domain Reflectometer (OTDR)
Visible Light Source Testing
Visible Light Source testing is used to test continuity in optical fiber strands. Optical fiber communication systems operate in the infrared region of the electromagnetic spectrum, which is invisible to the human eye. However, visible light sources are available for testing and troubleshooting optical fiber systems. They are also referred to as visual fault finders or visual fault locators.
To test using a visible light source, follow these steps:
- Connect the optical fiber flashlight to one end of a fiber strand (with most units, the fiber must be terminated).
- Look at the opposite end.
- If the light is not visible at the opposite end, a break or other problem is likely present somewhere along the length of the fiber. In many instances, the fault location will glow red from the light of the visible light source.
- Document the test result information.
Warning: Be careful not to look directly at active optical fiber strands. Laser light sources can cause serious eye damage.
Power-Meter-and-Light-Source Testing: The Key to Accurate Measurement of Fiber Attenuation
The proper testing of Optical Fiber Cable is essential to maximize the system’s longevity, minimize system downtime, reduce maintenance needs, and support system upgrades and reconfigurations. Testing optical fiber cable is critical for detecting any breaks, faults, or attenuation in the fiber, which could impact the overall performance of the system. Among the three most commonly performed test methods for Optical Fiber, Power-Meter-and-Light-Source Testing (also known as the One Jumper Method) is the most accurate way to measure end-to-end signal loss of the fiber, referred to as attenuation.
What is Power-Meter-and-Light-Source Testing?
Power-Meter-and-Light-Source Testing is a method of testing the attenuation of Optical Fiber Cable. It involves the use of a light source, a power meter, and a single jumper to measure the end-to-end signal loss of the fiber. The test results are then compared to the link attenuation allowance to determine the system’s performance.
How to Perform Power-Meter-and-Light-Source Testing?
To perform Power-Meter-and-Light-Source Testing, the following steps should be taken:
- Disconnect active equipment to avoid any damage.
- Acquire a suitable light source for the single mode and multimode fiber.
- Verify the proper wavelength to set the source and meter.
- Acquire accurate test jumpers and couplers, which should be part of the light source and power meter kit.
- Connect the jumper (containing the same fiber size as the system fiber) to the optical source and the optical power meter. Turn on the unit and record the reference power reading (Pref), displayed in dBm.
- Insert a second jumper (Test jumper 2) between the jumper used in Step 5 and the optical power meter. Verify that the attenuation added by the second jumper is not greater than 0.75 dB: Pref – Pcheck ≤ 0.75 dB.
- Attach the jumpers to the optical source and optical power meter. Connect the optical source/Test jumper 1 to one end of the system fiber to be tested. Connect the optical power meter/Test jumper 2 to the other end of the system fiber. Document the test power (Ptest).
- Subtract the test power (Ptest) from the reference power (Pref) to conclude the end-to-end attenuation: Attenuation (dB) = Pref – Ptest.
- Document the test results.
Loss Budget and Link Attenuation Allowance
| Element | Insertion Loss |
| Splice | < 0.3 dB at all wavelengths |
| Connector Pair | < 0.75 dB at all wavelengths |
Test results should be compared to the link attenuation allowance calculated as follows:
Link Attenuation Allowance (dB) = Cable Attenuation Allowance (dB) + Connector Insertion Loss Allowance (dB) + Splice Insertion Loss Allowance (dB) Where:
• Cable Attenuation Allowance (dB) = Maximum Attenuation (dB/km) x Length (km)
• Connector Insertion Loss Allowance (dB) = Number of Connector Pairs x Connector Loss Allowance (dB)
• Splice Insertion Loss Allowance (dB) = Number of Splices x Splice Loss Allowance (dB)
Conclusion
Power-Meter-and-Light-Source Testing is a crucial test method for the proper functioning of Optical Fiber Cable. With the right equipment, accurate test jumpers, and proper calibration, you can measure the attenuation of your system effectively. By comparing your test results to the link attenuation allowance, you can ensure that your system is performing optimally and that any issues are detected and resolved quickly.
Optical Time Domain Reflectometer (OTDR) Testing
Optical Time Domain Reflectometer (OTDR) testing is a valuable tool for measuring the length, attenuation, and events along the length of a fiber cable. By sending light pulses down the cable and measuring the timing and power of light reflected back to the OTDR, it creates a trace that displays a graph of power versus distance. In this article, we will explore the features and benefits of OTDR testing, as well as important factors to consider when using it for certification testing in a premises cable environment.
How does OTDR testing work?
OTDR testing sends light pulses down the fiber cable and measures the reflected light at different points along the cable. The OTDR uses this information to create a trace, which is a graph of power versus distance. The trace shows the length of the cable, as well as any attenuation or events along the length of the fiber. OTDR testing is particularly useful for troubleshooting because it provides a visual graph of the fiber.
Why use an OTDR?
An OTDR is an indirect measurement method and is not as accurate as a light source and power meter for measuring attenuation. However, it has several advantages that make it a valuable tool for testing fiber cables. Some of these advantages include:
- Measures the length of the cable.
- Provides a graph of power versus distance.
- Identifies attenuation and events along the length of the fiber.
- Helps with troubleshooting.
Like a power meter and light source, an OTDR tests at specific wavelengths (generally 1310 nm and/or 1550 nm for single mode and 850 nm or 1300 nm for multimode).
Important factors to consider when using an OTDR for certification testing
When using an OTDR for certification testing in a premises cable environment, it is important to consider the following factors:
- All fibers should be tested from both ends to ensure compliance end to end
- If measuring individual splice loss, always measure the splice from both directions and average the two measurements
- The shorter the measurement distance, the less accurate the attenuation measurement becomes
Conclusion
In conclusion, OTDR testing is a valuable tool for measuring the length, attenuation, and events along the length of a fiber cable. While it may not be as accurate as a light source and power meter for measuring attenuation, it has several advantages that make it useful for testing fiber cables. When using an OTDR for certification testing in a premises cable environment, it is important to consider the factors mentioned above to ensure accurate testing results.