What is a Fiber-Optic Attenuator?

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  • Written By: Mal Baxter
  • Edited By: Daniel Lindley
  • Last Modified Date: 05 October 2019
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Light waves travel through optical fibers carrying binary, or digital information, in computer and telecommunications networks. These networks can be made of many linked components between senders and receivers, as well as almost any length of optical fiber. Light created from lasers or light emitting diodes (LED) loses energy along the path of the network; for example through scatter, absorption, interference or reflection. Insertion loss and return loss, or back reflection, are collectively referred to as attenuation; total attenuation is called system loss. A fiber-optic attenuator is a fiber-coupled component that modulates an adjustable loss, permitting the optimal light signal strength for the needs of the network.

Measured in decibels (dB), attenuation can degrade signal clarity or result in network failure. Extrinsic attenuation, or transmission loss, may be caused by external factors imposing on the fiber, such as faulty network configurations. Intrinsic attenuation is created by manufacturing impurities in the fiber that can absorb or scatter light.

Attenuation, or loss, is measured in decibels as transmitted power minus received power. This loss depends also on direction, as results may differ measuring from A to B than loss from B to A. Attenuation across the span of a network can result from factors such as improper connection, bend radius, splicing, or end face preparation. These can result in scattering or interference effects. A fiber-optic attenuator provides desirable attenuation to modulate signal strength, by passively decreasing the amplitude of a light beam without altering the waveform.


Fiber-optic attenuator components serve single-mode and multimode fibers across industry standard product ranges. Plug fiber attenuators utilize male/female ceramic ferrule connectors. Fixed value attenuators function at one loss level, while variable attenuators like the variable optical attenuated jumper (VOA) can adjust loss in a range, as by a turning screw. Patch cord attenuators are fibers that combine the functions of the patch cord and attenuator, reducing costs.

The hybrid fiber-optic attenuator connects male-to-female connectors, while the bulkhead type provides a female-to-female link for two male-connecting fibers. Loopback attenuators allow production testing of simulated losses. Three-step attenuators are passive attenuators that fit onto existing fibers, utilizing a bending radius to achieve attenuation without back reflection. Other types of attenuators include the air gap and clip-on types.

The proper connector type for a given situation is indicated by decibels. For example, reducing optical intensity by 5 decibels would require a -5 dB attenuator. These components are employed in telecommunications networks, local area networks (LAN), and cable television (CATV) systems. Fiber-optic attenuator components can also be used in fiber-optic sensors, testing instruments, and fiber to the home. Compact, environmentally sound, and suffering low return losses, these devices can be embedded into optical fiber networks fitted to the wide variety of industry standard connectors and fibers.


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