If you have ever seen a telephone company technician working on the phone jump box outside your house, you should have noticed a special handheld phone like instrument. The technician uses it to identify the incoming telephone wires by tapping onto the wires and listening for a tone. Once he finds the correct wire, he connects the wire into your house.



During fiber optic network installation, maintenance, or restoration, it is also often necessary to identify a specific fiber without disrupting live service. This battery powered instrument looks like a longhandheld bar and is called fiber identifier or live fiber identifier.

:: How does it work?

There is a slot on the top of a fiber optic identifier. The fiber under test is inserted into the slot, then the fiber identifier performs a macro-bend on the fiber. The macro-bend makes some light leak out from the fiber and the optical sensor detects it. The detector can detect both the presence of light and the direction of light.

A fiber optic identifier can detect "no signal", "tone" or "traffic" and it also indicates the traffic direction.

The optical signal loss induced by this technique is so small, usually at 1dB level, that it doesn't cause any trouble on the live traffic.

:: What kind of fiber cables does it support?

Fiber optic identifiers can detect 250um bare fibers, 900um tight buffered fibers, 2.0mm fiber cables, 3.0mm fiber cables, bare fiber ribbons and jacketed fiber ribbons.

Most fiber identifiers need to change a head adapter in order to support all these kinds of fibers and cables. While some other models are cleverly designed and they don't need to change the head adapter at all.

Some models only support single mode fibers and others can support both single mode and multimode fibers.

:: What is relative power measurement

Most high end fiber optic identifiers are equipped with a LCD display which can display the optical power detected. However, this power measurement cannot be used as a accurate absolute power measurement of the optical signal due to inconsistencies in fiber optic cables and the impact of user technique on the measurements.

But this power measurement can be used to compare power levels on different fiber links which have same type of fiber optic cable. This relative power measurement has a lot of applications as described below.

:: Sample applications

1. Identification of fibers

The relative power reading can be used to aid in the identification of a live optical fiber.There are several tests that can be performed to isolate the desired fiber cable from a group of fibers without taking down the link(s). Three methods that could be used include comparing relative power, inducing macrobends, and varying the optical power of the source. No single method is best or necessarily definitive. Using one or a combination of these methods may be needed to isolate the fiber.

2. Identification of high loss points

Fiber optic identifier's relative power measurement capability can be used to identify high loss point(s) in a length of fiber. By taking relative power measurements along a section of optical fiber that is suspected of having a high loss point such as a fracture or tight bend, the change in relative power point to point can be noted. If a sudden drop or increase in relative power between two points is noted, a high loss point probably exists between the two points. The user can then narrow in on the point by taking further measurements between the two points.

3. Verify optical splices and connectors

Fiber optic identifier can be used to verify fiber optic connectors and splices. This test must be performed on a lit optical fiber. The optical fiber can be carrying a signal or be illuminated using an optical test source. Attach fiber identifier to one side of the optical connector/splice. Read and record the relative optical power. Repeat the measurement on the second side of the connector/splice. Take the difference between the reading on the second side and the first side. The difference should be roughly equal to the optical attenuation of the optical connector/splice. The measurement can be taken several times and averaged to improve accuracy. If the optical fiber identifier indicates high loss, the connector/slice may be defective.

:: Manufactures supplying fiber optic identifiers

You can get fiber optic identifiers from Wilcom, Ideal, 3M, Fitel, Noyes and many more manufacturers. We prefer Wilcom and Fitel products since both manufacturers have very high customer satisfaction rate.