Fact Checked

What Is an Optical Attenuator?

Andrew Kirmayer
Andrew Kirmayer

An optical attenuator decreases the strength of an optical signal passing through it to a fiber optic cable or open air. The intensity of the signal is described in decibels over a specific distance the signal travels. It is the strength, or amplitude of the signal that changes and not the overall waveform or frequency, so the optical signal remains undistorted for use in the desired application. Optical attenuators are often used in optical communication systems, in which the attenuation, also called transmission loss, helps with the long-distance transmission of digital signals. The most common optical attenuator types include fixed and continuously variable attenuators.

Often installed where signals are transmitted from, an optical attenuator can apply the principle of gap loss so the signal intensity is lowered to the optimal level over a given distance. Attenuators installed elsewhere along the optical fiber will not lower the signal strength enough, but some devices utilize signal absorbing or reflecting components to compensate. An optical fiber connector is often attached to the optical attenuator which typically has an adapter with a female configuration. The attenuator itself usually has a cylindrical or even box-like structural shape which determines the type of equipment in which it can be installed.

A variable optical attenuator can be mounted on a printed circuit board.
A variable optical attenuator can be mounted on a printed circuit board.

The fixed variety of optical attenuator, sometimes found in an electronic circuit, does not reflect light signals to reduce their intensity. It is generally used where the transmission of data needs to be highly accurate. The device’s function is determined by the amount of power it can handle in addition to important variables such as performance versus temperature and frequency range. Most optical attenuators utilize resistors, but a variable optical attenuator uses metal semiconductor field effect transistors or other solid state components. Attenuation intensity is adjustable so the signals in a fiber optic communication system can be changed to accommodate fluctuating power levels, protecting the system from damage.

A variable optical attenuator can be mounted on a printed circuit board, or used in test devices such as an optical power meter. Many attenuators are installed in-line with an optical fiber cable in order to adjust the transmitted signal accordingly. They are sold by many retailers and manufacturers online so one can assess their characteristics by reading the product specifications. Aspects to consider include the average and peak power the device can tolerate, how much attenuation it provides, as well as its overall dimensions and the type of environment it can operate in.

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Discussion Comments


@allenJo - I believe that all signals will experience loss over distance, whether you’re talking about light, electricity or radio waves.

Therefore you would need some system of modifying the signal I would think. Judging from the article, it seems that the variable optical attenuator would be the most useful of all the different versions of this device.

You can modify the amount of light, kind of like you would with a light dimmer switch. You could just keep adjusting it until you get just the right amount of signal for your component.


@miriam98 - Actually, it appears that the variable optical attenuator mentioned in the article does work to prevent system damage. So I think the comparison is valid, although I don’t know that it works with current levels comparable to what you kick out of a typical substation.

The only thing I’ve never understood is why you needed to reduce the power level of the light. I’d think you could probably set the proper light levels to begin with so that it wouldn’t need any alteration.

I always thought that fiber optic transmissions didn’t need any kind of moderation of the light signals in anyway, but apparently I was mistaken.


This is a good introduction to the optical attenuator function. It kind of reminds me of something we have in the electrical utility industry, which is the business I work in.

We have step down transformers. They take the electric current that comes from the power station and step it down so that it’s low enough to be delivered to the average household, at around 110 to 120 volts of alternating current.

If it’s not stepped down, it could do severe damage to your house. I don’t think that the optical attenuator poses comparable threats if it doesn’t work properly; my only guess is that the circuit would be overloaded. But still, I think it’s a similar concept.

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    • A variable optical attenuator can be mounted on a printed circuit board.
      By: Artwell
      A variable optical attenuator can be mounted on a printed circuit board.