Live Fiber Detectors: New Technologies Meet CO Challenges
Vincent Racine, Product Manager, Optical Business Unit
As today’s central offices (COs) continue to expand and to upgrade equipment and technologies, their complexity also increases. The multiplication of rack shelves, which includes transmission equipment, often involves the addition of new patch panels and interconnection points. These interconnection points bring more flexibility to the networks, as they allow for a quick rerouting of the signal and upgradeability of the whole system.
Among other things, this increasing system complexity brings about significant fiber-management issues. This is particularly true when fiber labeling practices are inconsistent—or even worse, non-existent. In these cases, unless technicians are equipped with the proper tool to correct the situation, the task of identifying fiber will seem insurmountable. Although a live fiber detector (LFD) is the instrument of choice for this job, traditional units present great limitations that may not make them entirely suitable for identifying a specific live fiber in a busy CO.
Different Fiber and Jacket Types
In today’s COs, various fiber types and jacket sizes are used, and they are often all mixed together—technicians may not have the knowledge or proper documentation to differentiate them. A traditional LFD will create a fixed bending radius that will force light to exit the fiber through the cladding and jacket. Detectors inside the instrument will then collect the light if the fiber is live.
Figure 1. Mechanical pull or push bends the fiber to a predetermined angle and forces light onto the detector.
In traditional LFDs, the bending radius may be adjusted by interchanging the head in the instrument jaw—various heads are engineered to accommodate different fiber types and jacket sizes.
Figure 2. Different heads enable the user to adjust the bending radius induced on the fiber under test.
Using the wrong head piece for a specific fiber type could lead to wrong measurements, as each head piece is designed to apply the appropriate bending radius for a specific fiber type. Therefore, using the wrong bending radius can result in one of the following:
- Overbend the fiber and create excessive loss; this can ultimately disturb or cut the traffic on the live fiber under test.
- Underbend the fiber, which will not allow enough light to exit the fiber; in this case, a live fiber may be identified as a dark one.
In both cases, the errors are costly. For instance, for a 16-channel wavelength-division multiplexing (WDM) system, downtime can cost up to US$160 000 per hour (assuming
US$10 000 per hour, per wavelength).
EXFO’s Innovative Intelligent Bending Technology
EXFO’s LFD-300 FiberFinder™ Live Fiber Identifier uses a step motor that gradually bends the fiber and simultaneously monitors the optical power level that escapes the fiber. By computing the position of the jaw, the instrument can recognize the bending radius applied to the fiber and can therefore self-adapt to the fiber type. With this technology, there is no longer the need to interchange heads, as was required with traditional LFDs—eliminating the risk of overbending or underbending, which could lead to costly network faults. The LFD-300 also ensures a low-loss operation (typically below 1 dB), allowing its use even on sensitive high-speed networks.
Figure 3. EXFO's LFD-300 is a fiber-detection unit that uses a motor, rather than human intervention,
to minimize loss and optimize readings.
Pinpointing a Specific Live Fiber
Traditional LFDs can identify if the fiber is live or dark. The main limitation comes when a user needs to pinpoint a specific live fiber among other live circuits. Traditional LFDs do not differentiate one live fiber from the others—the LFD will simply indicate that they are all live (carrying traffic). EXFO’s innovative LFD-300 FiberFinder™, combined with the TG-300 Tone Generator, enables technicians to pinpoint a specific live fiber—without having to disconnect it and, above all, without having to guess. This advantage brings key benefits such as no more network outages as a result of fiber detection/identification procedures and a minimized need to access the network, helping prevent errors.
How Does FiberFinder™ Work?
The TG-300 adds a typical 0.25 dB signature to the live signal by applying a soft low-frequency modulation pressure to the fiber. The instrument induces a low frequency, modulated over the traffic. Using a low-modulation scheme guarantees that the traffic carried by the fiber will not be disturbed, which, for example, is typically well above 2.5 GHz for OC-48 systems. This signature is then detected at the other end by the LFD-300, in mere seconds.
Figure 4. EXFO's TG-300 induces a low-frequency modulation while the LFD-300 FiberFinder™ detects the modulated signal to pinpoint specific live fiber.
EXFO’s innovative FiberFinder™ is the only solution that allows technicians to perform typical live fiber functions as well as pinpoint a specific live fiber among other live fibers, efficiently putting an end to guesswork in the CO. Thanks to its step-motor technology, the FiberFinder™ also prevents the inducement of excessive loss, which avoids disturbing busy systems such as 40 Gbit/s and dense wavelength-division multiplexing networks |