What Is an Optical Attenuator?

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.

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.