Insertion Loss
Definition: power losses due to insertion of a device
German: Einfügedämpfung
Categories: general optics, fiber optics and waveguides
Units: %, dB
How to cite the article; suggest additional literature
Author: Dr. Rüdiger Paschotta
If an optical device is inserted into a setup, some of the optical power may be lost in the device or at optical interfaces. Some examples:
- A fiber connector, a mechanical splice or a fusion splice may be used to connect two fibers, instead of having a single continuous fiber. Some of the optical power will be lost due to non-perfect interfaces, not exactly matching effective mode areas or similar factors.
- A Faraday isolator is inserted after the output of a laser in order to prevent it against back-reflections. Some power is lost at imperfect anti-reflection coatings of the isolator and possibly by parasitic absorption or scattering in the optical elements.
The insertion loss (or attenuation) is usually specified in decibels, calculated as 10 times the logarithm of base 10 of the ratio of output and input powers. For fiber connectors, for example, it is often of the order of 0.5 dB. High-quality fusion splices may reach values like 0.02 dB.
For high-power devices, a high insertion loss is often unwanted not only due to the power loss but also because of possibly strong heating effects resulting from absorbed light.
A convenient method for measuring insertion loss is optical time-domain reflectometry. With that, the insertion loss of multiple optical elements along a fiber can be measured separately.
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See also: fiber connectors, fusion splicing of fibers, decibel, return loss, optical time-domain reflectometers
and other articles in the categories general optics, fiber optics and waveguides
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