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Black Box Explains...Fiber optic attenuators

Attenuators are used with single-mode fiber optic devices and cable to filter the strength of the fiber optic signal. Depending on the type of attenuator attached to the devices at each end of the fiber optic cable, you can diminish the strength of the light signal a variable amount, measured in decibels (dB).

Why would you want to filter the strength of the fiber optic signal? Single-mode fiber is designed to carry a fiber optic signal long distances—as much as 70 kilometers (or 43.4 miles). Fiber devices send this signal with great force to ensure that the signal, and your data, arrive at the other end intact.

But when two fiber devices connected with single-mode fiber cable are close to each other, the signal may be too strong. As a result, the light signal reflects back down the fiber cable. Data can be corrupted and transmissions can be faulty. A signal that is too strong can even damage the attached equipment.

Because it’s probably not feasible to move your fiber equipment farther apart, the easiest solution is to attach an attenuator to each fiber device. Just as sunglasses filter the strength of sunlight, attenuators filter the strength of the light signal transmitted along single-mode fiber cable. Within the attenuator, there’s doping that reduces the strength of the signal passing through the fiber connection and minute air gaps where the two fibers meet. Fiber grooves may also be intentionally misaligned by several microns—but only enough to slow the fiber optic signal to an acceptable rate as it travels down the cable.

Before selecting an attenuator, you need to check the type of adapter on your fiber devices. Attenuators typically fit into any patch panel equipped with FC, SC, or LC adapters that contain either PC or APC contacts. In addition to the type of adapter, you also need to determine the necessary attenuation value, such as 5 or 10 dB. This value varies, depending on the strength of fiber optic signal desired.