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

Safety in Fiber Optic Installations

Fiber optic cables are now widely employed for the purpose of enhancing voice and data communication in many different applications. The flexibility of the technology is extraordinary, and advances in methods of communication have revealed even more uses for fiber optics. However, not all people, who install or maintain fiber optic cables, take proper safety precautions to avoid the hazards caused by fiber optics. Sometimes they just ignore the potential dangers of optical fiber. Unfortunately, accidents occur because of this neglect. This article will emphasize on introducing some common hazards that come with fiber optic installations and offering rules for safe installation.

Hazards of Working with Fiber Optics

The part will describe elements involved in safety protection issues when working with fiber optics. These are eye safety, bare fiber safety and other considerations for safety.

Eye Safety

Many people are concerned that the most dangerous part of fiber-optic work was the chance you might get your eyes harmed by laser light in the fiber. However, in fact, most fiber-optic systems do not have sufficient power to cause harm to your eyes and the light coming out of a fiber is expanding, so the farther you are away from the end of the fiber, the lower the exposure.

However, it’s not a good idea to look into a fiber unless you know no source is being transmitted down it. You should always check the fiber with a power meter before examining it. The real issue of eye safety is getting fiber scraps into the eye. During the process of termination and splicing, you will be continually exposed to small scraps of bare fiber. And these scraps are very dangerous. Once they get into your eyes, they are very hard to flush out and will probably lead to a trip to the emergency room at the hospital. Whenever you are working with fiber, wear safety glasses!

Bare Fiber Safety

The fibers themselves are a very serious hazard since they are small pieces of glass. If possible, use a dark plastic mat for a work surface, which will make it easier to see the fibers you are working with and handle them more carefully.

When trimming, stripping, or cutting fibers, tiny fragments can penetrate the skin and become embedded, causing a serious irritation. Ingested fibers can cause internal damage since they are light enough to float in air. Because of this, workers should not eat or drink in a fiber optic work area since a fiber scrap could fall onto their food or in their drink.

Other Considerations for Safety

Fiber optic splicing and termination use various chemical cleaners and adhesives as part of the processes. And these substances should be properly handled. Note that fusion splicers use an electric arc to make splices, so one should ensure no flammable gases are contained in the space where fusion splicing is done. Smoking should not be allowed around fiber optic work.

Fiber Optic Installation Safety Rules

• Keep all food and beverages out of the work area in case fiber particles are ingested
• Wear disposable aprons to minimize fiber particles on your clothing. Fiber particles on your clothing can later get into food, drinks, and/or be ingested by other means.
• Always wear safety glasses with side shields and protective gloves. Treat fiber optic splinters the same as you would glass splinters.
• Never look directly into the end of fiber cables until you are positive that there is no light source at the other end. Use a fiber optic power meter to make certain the fiber is dark. When using an optical tracer or continuity checker, look at the fiber from an angle at least 6 inches away from your eye to determine if the visible light is present.
• Only work in well ventilated areas.
• Contact wearers must not handle their lenses until they have thoroughly washed their hands.
• Do not touch your eyes while working with fiber optic systems until they have been thoroughly washed.
• Keep all combustible materials safely away from the curing ovens.
• Put all cut fiber pieces in a safe place.
• Thoroughly clean your work area when you are done.
• Do not smoke while working with fiber optic systems.

Conclusion

In conclusion, the awareness of safety should be raised among fiber optic installers, and each technician must adopt the best practices for safe handling of all fiber optic components to preserve the safe environment. Hope these simple fiber optic safety rules can contribute to building a healthy and sound work space.

First published: http://www.china-cable-suppliers.com/safety-in-fiber-optic-installations.html