Traditional live fiber detectors (LFDs) use thumb-activated fiber bending at a fixed angle to enable the detector to read the power leaking from the jacket (see Figure 1). Since the bending is fixed and optimized for one wavelength and one fiber type, the bending often causes:
In addition to being unreliable, the fact that they can cause excessive loss is the main reason why traditional LFDs are considered dangerous and are not used on high-data-rate routes and in long-haul-network applications.
EXFO’s LFD-250B Live Fiber Detector introduces step-motor-activated bending and makes fixed-angle bending—and the drawbacks stated above—a thing of the past.
For all fiber types and all wavelengths, insertion loss is monitored as a function of the bending angle as the motor (and not human power) moves. Although the angles differ, the behavior remains the same. The adjacent graph shows that fixed-angle bending generates excessive loss in some cases, and leads to flawed identification in others.
The LFD-250B brings a unique approach: the power loss is monitored as the motor (and not human power) changes the angle. Therefore, the angle is automatically optimized for each fiber type and each singlemode wavelength. This results in clear-cut advantages:
EXFO’s LFD-250B performs an ambient light offset prior to fiber bending, which makes it less sensitive to ambient light. A push-down cap can also be placed on the headend to block intense ambient light.
As stated, the LFD-250B controls the insertion loss within the fiber (IL) in dB. But the absolute value of the measured signal is in dBm, so knowing the loss in dB and the power level of this light exiting, power can be measured with a better accuracy than traditional fixed loss LFDs. Of course, coupling efficiency is a factor (3 mm jackets absorb more than 1.6 mm and 900 μm jackets). However, since loss is monitored as a basis for motor positioning, the unit knows what size of jacket is being tested (either 900 μm, 1.6 mm or 3 mm), so the LFD-250B automatically uses the proper coupling efficiency parameter and computes the power within any fiber, at any wavelength, with 1 dB repeatability.
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