Best budget-friendly optical reflectometer

In recent decades, the rapid development of optical fiber communication (OFC) lines has required simple, reliable instruments for diagnosing optical communications. An optical time domain reflectometer (OTDR) is one of the most common devices for testing fiber optic links and identifying problem areas in fiber optic communication lines. What criteria should be used to choose a reflectometer so that it performs correctly and does not require excessive financial investments?

Reflectometer: luminous intensity

A reflectometer directs a beam of laser light into an optical fiber. Then, it measures the parameters of the reflected light, thus analyzing the characteristics of the optical fiber. This way, one can not only detect but also determine the location of any damage to the fiber optic line: a lousy receptacle or connector, a cable bend, light loss, poor splicing, etc.

This is a very effective technology, but it has two severe limitations. First, the reflectometer's probe pulse is reflected from all connectors, including the first one, which is why "lighting" creates a dead zone in which measuring is impossible. This problem is solved using an additional piece of optical fiber (launch cable) connected to the line under test. The dead zone is on this fiber, and the entire line can be tested. It is necessary to consider the length of the line that is supposed to be tested and select the correct length of the compensation coil; sometimes, the length can reach several miles.

The second limitation is that different types of optical fiber have the highest light reflectance coefficient at different wavelengths. Of course, the best choice seems to be the most versatile device that can operate in a wide range of wavelengths, for example, from 850 nm to 1650 nm. In particular, the VIAVI MTS-8000 universal measuring platform and a set of modules capable of solving almost any problem of fiber-optic communication analysis.

One must keep in mind that expanding the capabilities dramatically increases the cost of the device. However, these capabilities are not always necessary. More straightforward solutions are often sufficient for checking and even last-mile optical line certification, such as an optical reflectometer with the tester function and damage visualizer Greenlee 930XC-20C-UPC-FC.

The situation is similar to the dynamic range—the strength of the reflectometer signal and its ability to detect even slight attenuation of the optical signal. This can result in a severe deterioration in the efficiency of fiber optic lines on long, critical lines. Therefore, more expensive reflectometers with a wide dynamic range are used to check them. Generally, an OTDR with a dynamic range of 6 dB is more excellent than the loss of the longest optical communication line that the OTDR will ever have to service, which is sufficient for reliable testing.

These are the main aspects to consider first when choosing a reflectometer. However, many reflectometer models are on the market, and selecting them is not always easy. Fortunately, there is a simple set of questions, and answering them will give you a "portrait" of the device best suited for a specific set of tasks.

The right questions to ask when choosing an optical reflectometer

First of all, you need to answer questions about using your new reflectometer:

• What networks and types of optical fiber will be tested (for example, multi-mode optical fiber or single-mode optical fiber)?
• What is the maximum length of the fiber-optic link to be tested?
• What measurements are aimed at (certification, troubleshooting, regular maintenance)?

The answer to these questions will significantly narrow the field of suitable reflectometers. For example, 850 nm and 1300 nm wavelengths are used for multi-mode optical fiber, and 1310 nm and 1550 nm are used for single-mode optical fiber. In the case of PON testing, wavelengths of 1490 nm and 1625 nm may be needed in addition to 1310 nm and 1550 nm.

If the reflectometer's main task is to localize damage, then buying an expensive device may be a waste of money.

However, if detailed diagnostics of a fiber-optic link and its certification are needed, professional reflectometers with a large dynamic range, small dead zones, and good software for processing reflectograms and generating a report are necessary.

It is also necessary to consider the aspects related to the device's operation. In particular, the size and weight of the reflectometer are directly related to the team's mobility. Devices with a larger screen (more than 5") are most often chosen for indoor work or as part of a mobile lab. Specialists use portable devices to work on city networks. Such devices must have waterproof housing and withstand a wide range of operating temperatures.

The minimum operating time on one battery charge is preferably at least 8 hours so that field measurements do not extend over two working days. The ability to upload data to the cloud for subsequent analysis and results processing will significantly save time.

Often, several instruments can be combined in one housing: a reflectometer, a tester, a damage visualizer, an optical spectrum analyzer, a dispersion analyzer, etc.

An important feature is the ability to expand the functionality and update the reflectometer software during operation, which means that a more expensive modular solution may be a more profitable purchase in the long term in some cases.