The Fiber Identifier
acts as the fiber optic installer or technician’s infrared eyes. By placing a slight macrobend in an optical fiber or fiber-optic cable, it can detect infrared light traveling through the optical fiber and determine the direction of light travel. Some fiber identifiers can also detect test pulses from an infrared (800–1700nm) light source.
The fiber identifier typically contains two photodiodes that are used to detect the infrared light. The photodiodes are mounted so that they will be on opposite ends of the macrobend of the optical fiber or fiber-optic cable being tested. The electronics in the fiber identifier measure the detected light energy and display the direction of light travel through the optical fiber.
The optical fiber identifier is used very much like the Fiber Locator (VFL) when it comes to troubleshooting. But there are two difference: One key difference is that the fiber identifier replaces your eyes. Another difference is that fiber optic cable under test typically does not have to be disconnected from an active circuit – it can remain plugged into the transmitter and receiver.The fiber identifier can typically be used with coated optical fiber, tight-buffered optical fiber, a single optical fiber cable, or a ribbon cable. Each of these must be placed in the center of the photodiodes during testing. Selecting the correct attachment for the optical fiber or optical-fiber cable type under test typically does this.
Figure 1 shows Fiber identifier optical fiber and fiber-optic cable attachments
The fiber identifier can also be used with external light source. Often the external light source is an Fiber OTDR
. Many OTDR manufacturers build or program in a pulsed output function. When set for a pulsed output, the OTDR emits a continuous pulse train at a predetermined frequency. The electronics in the fiber identifier can detect preset frequencies and illuminate the corresponding LED. This feature can be very helpful when you are trying to identify an unmarked tight-buffered optical fiber within a bundle of tight-buffered optical fibers. This feature can also be helpful when you are trying to approximate the location of a break in the optical fiber.
The fiber identifier can be used with the OTDR to narrow down the location of a break in an optical fiber when a VFL is not available or when the light from the VFL is not visible through the jacket of the fiber optic cable. If the index of refraction is correct, the OTDR should provide an accurate distance to the fault. The OTDR measures the length of optical fiber to the fault, not the length of fiber optic cable. The cable length may be shorter than the optical fiber length.
Once you have found the approximate location of the fault with the OTDR, set the OTDR or infrared light source to pulse at a predetermined frequency. Clamp the fibr identifier on the faulted fiber optic cable several meters before the approximate location of the fault. Check the fiber identifier for the predetermined frequency. If the fiber identifier does not detect the predetermined frequency, move the fiber identifier several meters closer to the OTDR or infrared light source and recheck for the predetermined pulse. If you have choosen the correct fiber optic cable test to the fault of the distance with you, you should be testing a predetermined frequency. If you still don’t test frequency, carefully check everything, and test again. If you still do not detect the predetermined frequency, there may not be enough optical energy for the fiber identifier to function properly.
Figure 2 shows optical fiber identifier
If you are able to detect the predetermined frequency, move the fiber identifier down the fiber optic cable away from the OTDR or infrared light source in one meter increments. Continue to do this until the fiber identifier no longer detects the predetermined pulse. You now know within one meter where the break in the optical fiber is located. At this point, you may want to disconnect the OTDR or infrared light source and connect the visible fault locator. The visible fault locator may illuminate the exact location of the fault. If the visible fault locator does not illuminate and conditions permit, darken the area around the fault. This may allow you to see the illuminated fault.