How to Choose a Perfect OTDR?

The past few years have witnessed the boom in optical fiber being used in network communication industry. In order to make sure that the fiber network is reliable and accessible, a more accurate and faster methodology for assessing the integrity of the infrastructure is indispensable. Therefore, it is essential to choose the right fiber optic testing tool/device: not only to meet the enhanced testing requirements, but also help to increase the reliability and value of the whole network. OTDR is one of the most powerful test instruments for fiber cable testing.

What Is OTDR?

OTDR (optical time-domain reflectometer) is used to test the performance of newly installed fiber links and detect problems that may exist in fiber links. The purpose of it is to detect, locate, and measure elements at any location on a fiber optic link. An OTDR needs access to only one end of the link and acts like an one-dimensional radar system. By providing pictorial trace signatures of the fibers under test, it’s possible to get a graphical representation of the entire fiber optic link.

Just by injecting pulsed of light into one end of a fiber and analyzing the back scattered and reflected signals, an OTDR can thus measure:

Optical Distance

• To elements: splices, connectors, splitters, multiplexers
• To faults
• To end of fiber

Loss, Optical Return Loss (ORL)/Reflectance

• Loss of splices and connectors
• ORL of link or section
• Reflectance of connectors
• Total fiber attenuation

Why Need an OTDR?

Fiber testing plays a significant role in ensuring the network is optimized to deliver reliable and robust services without fault.

For Outside Plants (OSP)

Service providers and network operators want to insure that their investments into fiber networks are protected. In outside fiber plant, every cable will be tested for end-to-end loss and with an OTDR to ensure the installation was properly made. Installers will be asked to use loss test sets (source and power meters) as well as OTDRs, performing bi-directional tests and providing accurate cable documentation to certify their work. Later, OTDRs can be used for troubleshooting problems such as break locations due to dig-ups.

For Premises, LAN/WAN, Data Centers, Enterprise

Premises fiber networks have tight loss budgets and less room for error. Installers should test the overall loss budget with a light source and power meter. OTDR testing is a best practice that can pinpoint the causes for excess loss and verify that splices and connections are within appropriate tolerances. It is also the only way to know the exact location of a fault or a break. Testing a fiber link with an OTDR also helps document the system for future verification.

Factors to Consider When Choosing the OTDR

For different test and measurement needs, there exist a great number of OTDR models, then how to select the right one? A comprehensive understanding of OTDR specifications and the application will help make the choice. Moreover, based on your specific need, you should answer the following questions before looking for an OTDR:

• What kind of networks will you be testing?
• What fiber type will you be testing? Multimode or single-mode?
• What is the maximum distance you might have to test?
• What kind of measurements will you perform? Construction, troubleshooting or in-service?

And when choosing an OTDR, you should take these factors into consideration:

• Size and Weight—important if you have to climb up a cell tower or work inside a building
• Display Size—5” should be the minimum requirement for a display size; OTDRs with smaller displays cost less but make OTDR trace analysis more difficult
• Battery Life—an OTDR should be usable for a day in the field; 8 hours should be the minimum
• Trace or Results Storage—128 MB should be the minimum internal memory with options for external storage such as external USB memory sticks
• Bluetooth and/or WiFi Wireless Technology—wireless connectivity enables easily exporting test results to PCs/laptops/tablets
• Modularity/Upgradability—a modular/upgradable platform will more easily match the evolution of your test needs; this may be costlier at the time of purchase but is less expensive in the long term
• Post-Processing Software Availability—although it is possible to edit and document your fibers from the test instrument, it is much easier and more convenient to analyze and document test results using post-processing software

Conclusion

An OTDR is a vital fiber optic tester for maintaining and troubleshooting optical infrastructures. When choosing your OTDR, first to figure out the applications that the OTDR will be used for, and then check the OTDR’s specification to see if it is suited to your applications. And don’t forget to consider those elements we stated in this article. Hope it would help when you hesitate to make your decision.

Originally published: http://www.fiber-optic-solutions.com/choose-perfect-otdr.html

Common Ways to Test Optical Fiber Cable

As the popularity of bandwidth-intensive applications has increased continuously, demand for fiber optic installations and infrastructures has accelerated parallelly. Optical fiber cable thus has possessed a rather essential position in telecom industry. However, the testing of optical fiber cable is often considered to be one of the most confusing and misunderstood phases of installing a fiber optic system, meanwhile it is also one of the final and most important procedures in installing optical network. Then how to deliver valid optical fiber cable testing? Here, we introduce you three most common methods.

Why Optical Fiber Cable Testing Matters

Let’s start by talking about the importance of optical fiber cable testing. Proper testing of optical fiber cable increases the system’s longevity, minimizes system downtime, reduces maintenance needs, and supports system upgrades and reconfigurations. And all these contribute significantly to your network performance, reliability and manageability in the long run.

Optical Fiber Cable Testing Methods

Fiber optic cable is tested to ensure continuity and attenuation. Basically, there are three test methods commonly performed for optical fiber: visible light source, power meter and light source (one jumper method), and optical time domain reflectometer (OTDR).

Visible Light Source Testing

Visible light source tests optical fiber continuity. Optical fiber communication systems operate in the infrared region of the electromagnetic spectrum which is invisible to the human eye. However, (red) visible light sources are available for testing and troubleshooting optical fiber systems. They are also referred to as visual fault locators and visual fault finders.

When testing optical fiber cable with a visible light source, you could follow the suggested procedures:

Step 1. Connect the optical fiber flashlight to one end of a fiber strand (with most units, the fiber must be terminated).

Step 2. Look at the opposite end. (Notice: Be careful not to look directly at active optical fiber strands. Laser light sources can cause serious eye damage.)

Step 3. 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.

Step 4. Document the test result information.

Power Meter and Light Source Testing

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. Listed below are TIA/EIA- 568 insertion loss limits for the various components. Specific installations or protocols may impose stricter limits.

Loss budget (TIA/EIA specification limits)

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)

When testing optical fiber cable with power meter and light source, perform the following steps.

Step 1. Disconnect active equipment.

Step 2. Acquire suitable light source for the single mode (generally 1310 nm or 1550 nm), multimode (850 nm or 1300 nm), and power meter.

Step 3. Verify proper wavelength to set source and meter. (Note: Calibration of the equipment is required before each test. Follow the equipment manufacturer’s procedures.)

Step 4. Acquire accurate test jumpers and couplers, which should be part of the light source and power meter kit.

Step 5. Connect the jumper (containing the same fiber size as the system fiber) to the optical source and the optical power meter. Turn unit on. Record the reference power reading (Pref), displayed in dBm.

Step 6. By applying an adapter, insert a second jumper (Test jumper 2) between the jumper used in Step 5 and the optical power meter. Verify the attenuation added by the second jumper is not greater than 0.75 dB: Pref-Pcheck ≤ 0.75 dB.

Step 7. Attach the jumpers to the optical source and optical power meter. Disconnect the two jumpers at the adapter. 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), recorded in Step 5, to conclude the end-to-end attenuation: Attenuation (dB) = Pref-Ptest.

Step 8. Document the test results.

Optical Time Domain Reflectometer (OTDR) Testing

Optical time domain reflectometer (OTDR) measures the fiber cable length, attenuation, and “events” along the length of the fiber. Here, the events can be splices, breaks, or stress points that cause excessive attenuation. The OTDR does this by sending light pulses down the cable and measuring the timing and power of light reflected back to the OTDR by the events and the fiber itself. It uses this information to display a “trace”, which is a graph of power versus distance.

An OTDR only requires access to one end of a fiber for testing. Because an OTDR is an indirect measurement method, it is not as accurate as a light source and power meter for measuring attenuation. However, due to its ability to display a graph of the fiber, it is particularly useful in 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).

Conclusion

Appropriate understanding of the testing methods and referencing procedures plays a critical role in testing accuracy for both legacy and future systems. Among these three methods mentioned in the article, which one to choose actually depends on your specific needs and real circumstances. Hope what we discussed above could fix your problems and assist you to deliver better optical fiber testing.

First published: http://www.fiber-optic-solutions.com/common-ways-test-optical-fiber-cable.html