# Fibre optic -physics

What is different between the lost of coupling and efficiency overall coupling ?

I know both of them (power out/power in)e.g (5%) that means is 5% light transmission and 95% lost.

• Where did you read these terms? As far as I know, "lost of coupling" is not a widely used term in the fiber optics field. We could talk about coupling efficiency and coupling loss, maybe. Oct 15 '20 at 19:57
• thanks for replaying me question.I believe, this calculation base on the measuring the power before the finer and after ?
– Sara
Oct 16 '20 at 0:24
• there are coupling efficiency and coupling loss, how to calculated it?
– Sara
Oct 16 '20 at 15:46

The coupling efficiency is the portion of the incoming light in the first fiber that is coupled to the desired mode(s) in the second fiber. $$\eta = \frac{P_{\rm out}}{P_{\rm in}}$$ Coupling efficiency is usually expressed as a numerical value (as shown above) or as a percentage. It might also be expressed in decibels.