Coupling efficiency

In optical fiber transmission, the ratio of the input optical power to the output optical power of an interface. For example, the ratio of the power emitted by the light source to the power received by the fiber optic bundle, or the ratio of the optical power received at the end of the fiber bundle to the power falling on the photodetector. For light sources whose emission surface is larger than the core diameter, the product of the numerical aperture NA of the fiber and the core diameter is the sign of the maximum coupling efficiency. For other light sources with an emitting area smaller than the core diameter, such as laser diodes, only NA can be used as a suitable indicator of coupling efficiency. The use of the tail-burning fiber for coupling with the light-emitting tube and the use of the tapered fiber for coupling with the laser tube is to increase the numerical aperture NA and improve the coupling efficiency.