RP Photonics

Encyclopedia … combined with a great Buyer's Guide!

VLib
Virtual
Library

Return Loss

Acronym: ORL

Definition: a measure for how much reflected light is attenuated

German: Reflexionsdämpfung

Category: general optics

Units: dB

How to cite the article; suggest additional literature

The return loss (or reflection loss) of some optical device (or a combination of devices) specifies how much lower the optical power of the returning (reflected) light is compared with the light sent into the device. Usually, the return loss is specified in decibels. For example, if the return loss is 30 dB, the returning light has only 1/1000 of the power of the incident light. Note that only directly returning light is counted – and no light which is reflected into a different direction, e.g. at an angle-cleaved fiber end.

The term return loss is most often used in cases where ideally there would be no reflected light at all. For example, a fiber coupler (which is a unidirectional coupler) should split the power of incident light between two or more outputs, but should not reflect any light back to the source (assuming that no light is reflected from its outputs). The return loss would then be infinite. However, some finite return loss (often many tens of decibels) may be caused, for example, when the fiber of the coupler has different guiding properties (refractive index, effective mode area, etc.) than the fibers spliced to the input and output of the fiber coupler. Also low-quality splices can lead to increased return loss. Good splices should have a return loss of at least 45 dB. With angle-cleaved splices, even substantially higher values are possible.

Similarly, a Faraday isolator would ideally not reflect any light, but some finite return loss results from imperfections. The actual return loss may be specified for a situation where all light from the output is reflected back to the isolator.

A fiber itself can have some finite return loss due to Rayleigh scattering.

Importance of High Return Loss

In various situations, it can be important that the return loss of some optical arrangement is sufficiently high. Some examples:

See also: fiber couplers, Faraday isolators, decibel, insertion loss, Rayleigh scattering
and other articles in the category general optics

How do you rate this article?

Click here to send us your feedback!

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent
Comments:

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you enter any personal data, this implies that you agree with storing it; we will use it only for the purpose of improving our website and possibly giving you a response; see also our declaration of data privacy.

If you like our website, you may also want to get our newsletters!

If you like this article, share it with your friends and colleagues, e.g. via social media:

arrow