Fiber Optic Test Methodology and Equipment
There is a plethora of test equipment available for fiber optic equipment & system testing. The most common and useful are the following: Optical power meter, Optical light source,puneng networks, Fiber fault locator, Optical connector inspection scopes and the Optical Time Domain Reflectometer (OTDR). This article will provide a brief overview of each of these and explain their purpose. However, before we begin, it is important to stress safety when working with fiber optics. All of the light sources used in fiber optic transmission in the AV, broadcast, telecom, etc. applications emit infrared light. That is, light that is invisible to the eye. While invisible, it can still be dangerous, depending on the power. Therefore, care must be taken, especially when using inspection scopes to ensure that any light source is turned off before looking at the end of any fiber.
Optical Power Meter (OPM)‐ The most basic and useful (and essential) of the test equipment is the optical power meter. This is equivalent to an electrician having a volt meter. The OPM allows you to measure optical transmitter output power, power at various junction (connector or patch panel) points, and receiver input power. In many cases, the optical power meter will be all that you need to properly diagnose a system problem and get the system up and running quickly. The optical power meter can provide an absolute measure of power in either micro or milliwatts (μW, mW) or dBm (power referenced to 1 mW). An absolute reading of 1mW is equivalent to 0dBm. Since most equipment uses dBm to indicate its optical power characteristics, the dBm scale on the power meter is the most convenient to use. Optical power meters will also have buttons to select the wavelength of the light they are measuring. There are selections for 850, 1300/1310 and 1550nm. It’s important to match the meter’s wavelength setting to that of the light you are measuring to ensure accurate readings.
Optical Light Source (OLS)– The OLS is generally a handheld or portable device that has different types of optical emitters that correspond to the type of fiber used in the system. fiber optic test light source will have emitters of both 850nm and 1300nm while singlemode OLS units will emit light at 1310nm and 1550nm. More flexible OLS units will have light sources applicable to both multimode and singlemode fiber. When used in conjunction with an OPM, the entire fiber infrastructure including fiber, splices and connectors can be tested at different wavelengths to verify the fiber installation’s integrity, without the need for any transmitter/receiver equipment. Since an OPM and OLS are used at different ends of the fiber, two persons are required to properly te st the fiber. Obviously, this can be difficult if adequate, trained personnel are not readily available. OLS prices range from $1K - $5K depending on type of source(s), LEDs and/or lasers and wavelengths.
Optical Time Domain Reflectometer (OTDR)– The OTDR is a versatile, one person instrument that identifies and quantifies events such as fiber distance & attenuation, connector and splice losses and fiber breaks. In addition, it will measure the distance to these events as well as the total length of the fiber. Some of these events are characterized as expected (such as connector loss) while some are unexpected, such as fiber breaks, sharp fiber‘kinks’ or tight bends, etc.
The OTDR works by sending very short, high intensity pulses of light down the fiber and measures the reflection or backscatter of this light as it propagates down the fiber. By measuring the time it takes for the pulse of light to return as well as its amplitude, the OTDR will calculate the distance to these events as well as the magnitude of each. It is a very versatile and effective way to perform single-ended testing and troubleshooting of a fiber link. While an optical loss test or OPM can only measure total loss of a fiber span including connectors, splices, etc, the OTDR can not only measure total loss but is the only instrument that can identify the location and size of any anomaly within the fiber span to better aid in quickly finding and repairing the problem. However, this versatility comes at a price. The cost of a basic, portable OTDR is in the range of $5-8K while the cost of a basic optical power meter is in the range of a few hundred dollars. While not for everyone, the OTDR can save time and money in diagnosing a fiber problem to ensure that system downtime is held to a minimum. While the OTDR is straightforward to use, it does require a higher set of skills and some initial training to help better understand its functions, capabilities and limitations. It is generally not a piece of equipment that most installers would have access to.
Fusion Splicer – A fiber optic fusion splicer is a device that uses an electric arc to melt two optical fibers together at their end faces, to form a single long fiber. The resulting joint, or fusion splice, permanently joins the two glass fibers end to end, so that optical light signals can pass from one fiber into the other with very little loss. Fusion splicing is the act of joining two optical fibers end-to-end using heat. The goal is to fuse the two fibers together in such a way that light passing through the fibers is not scattered or reflected back by the splice, and so that the splice and the region surrounding it are almost as strong as the virgin fiber itself. The source of heat is usually an electric arc, but can also be a laser, or a gas flame, or a tungsten filament through which current is passed.
FiberStore offer a selection of Fiber Testers & Tools to fit any fiber optic cable lineman or powerline worker jobs. We stock top high quality Test Equipment for the communications applications. In the fiber optic installation and maintenance works, Optical Power Meters, Fiber Light Sources, Fiber Scopes and OTDR are commonly used for fiber optic testing. And Splicing fiber tools, termination tool kits and cleaning tools, like strippers, cable cutters, splice protective sleeves help work easier. We not only provide well-known brands such as CLETOP, EXFO, Noyes, AFL and many more, but also offer innovative, high quality products to lower costs.
