In any complex system testing and maintenance plays a vital role in keeping the system functioning at peak efficiency and fiber-optic networks are no exception. Over the years a wide variety of equipment has evolved for use in testing troubleshooting and documenting fiber optic spans. Ranging from simple power meters inspection equipment and fiber identifiers to more complex and expensive instruments such as orders.
Today’s fiber technician must be well-versed on the various test instruments available. As well as the procedures used in the practical testing of fiber optic networks.
Loss measurements fiber networks:
The most common tests performed on fiber networks are loss measurements. Using a light source and power meter and fiber span analysis using an OTDR. Each measurement method has strengths as well as weaknesses. OTDR measurements can be made quickly by one person. And can provide details on the condition of all splices connectors and the fiber of a particular span.
Its greatest strength is the ability to zero in on individual events. Along the span and provide attenuation and reflectivity information for the event. However, attenuation values provided by an OTDR are not based on direct measurement methods. But rather from calculations on the levels of backscattered light returning to the OTDR. Although this allows the instrument to measure very low attenuation values of events such as individual fusion splices. It is not the best way to measure the total attenuation of an entire span.
The light source & Power meter:
The light source and power meter, however, displays attenuation values by directly measuring the amount of light. Passing through a fiber under test and can thus provide very accurate attenuation readings. Optical loss testing often requires two people one at the launch end and the other at the receiving end of the fiber. The primary function of the optical loss test is to verify the end-to-end attenuation of the fiber-optic link. Including the fiber connector’s splices and passive components.
In addition, the power meter can be used for simple continuity checks. Light sources and power meters are the essential go/no-go in for fiber optics testing. The EIA 455 and IEC 793 series of test standards have been developed to standardize fiber optic test procedures. Conforming to these standards will ensure accurate system measurements for a variety of tests on both components and systems. As the principal task of optical loss testing is to measure attenuation the DB is the term most commonly used.
Function of DB:
The DB represents a signal loss or gain in terms of power ratio shown by this formula. DB equals 10 log of the output power divided by the input power because it represents a ratio a decibel is a relative unit. When using DB to express absolute power levels the decibel value must be qualified by a reference. When making power measurements such as transmitter power levels or the amount of optical power at receivers.
The term DBM is used absolute optical power is expressed in DBM or decibels reference to one Mila watt. While DB represents a percentage loss or gain thus DBM minus DB M equals DB. For example, if 0 DBM equals 1 Mila watt then minus 10 DBM is 1/10 of 1 Mila watt. Or 100 microwatts and +10 DBM is 10 times 1 Mila watt or 10 Mila watts. Optical loss testing must be performed when a fiber system is first installed to verify fiber continuity. Validate correct polarity and certify that the attenuation of each fiber meets design specifications.
Testing is then performed periodically as the system ages or is modified by changes to verify that attenuation stays within tolerance. It is important that all tests be fully documented so that future tests can be quickly compared to previous values. Any increases in attenuation over time may be a sign of trouble that should be addressed before it causes a system failure. Although simple in nature successful optical loss testing requires high-quality equipment and test jumpers.
Other considerations include the type of optical detector equipment size and weight temperature stability and warm-up performance. Ruggedness for field use the type of connectors used a CDC operation battery life PC interface and whether the instrument reads in DB DBM or Mila watts. Readings and Mila watts are often required in laboratory and cable TV applications.
One of the most important considerations is how the test instruments will be used in the application? When selecting the type of optical loss test equipment to be used time and labor issues must also be considered. Inland applications, For example, the fiber distances between buildings may be relatively short. So one would think that an inexpensive single Direction source and power meter would be adequate for the application and would provide the user with a low-cost option.
Obstacles & restrictions:
In practice, however, these savings may not be realized if there are obstacles or restrictions such as multiple floors doors and security checkpoints. That slows down technicians trying to make multiple measurements from both ends of each fiber span throughout the campus. a fiber intensive installation like fiber to the desk may justify spending more for tests equipment that automates the testing certification and documentation process.
In longer haul applications such as wide area networks where fiber spans may be many miles performing tests in one direction. Than swapping locations will result in many wasted hours of travel time. A metropolitan area networks where fiber distances may be nominal parking problems and traffic jams will slow the testing process. In these cases, it would be more cost-effective to purchase bi-directional test sets. The simplicity reliability and cost-effectiveness of optical loss testing makes it the cornerstone of all fiber optic tests and measurements properly performed.
It will provide you with a powerful tool to ensure the continued success of your fiber optic system.