For example, in a popular home experiment, a glass rod is made almost invisible by immersing it in an index-matched transparent fluid such as mineral spirits.
In fiber optics and telecommunications, an index-matching material may be used in conjunction with pairs of mated connectors or with mechanical splices to reduce signal reflected in the guided mode (known as return loss) (see Optical fiber connector).
Without the use of an index-matching material, Fresnel reflections will occur at the smooth end faces of a fiber unless there is no fiber-air interface or other significant mismatch in refractive index.
However, certain digital transmitters such as those employing a Distributed Feedback Laser may be affected by back reflection and then fall outside specifications such as Side Mode Suppression Ratio, potentially degrading system bit error ratio, so networking standards intended for DFB lasers may specify a back-reflection tolerance such as −10 dB for transmitters so that they remain within specification even without index matching.
Similarly, losses (missing sections) in transparent or semitransparent objects are often filled using an index-matched material.
Historically, Canada balsam was used in this application, but it is now more common to use epoxy or other synthetic adhesives.