Launching light into fiber cores from sources located in the cladding

The problem of the efficiency of light injection into the cores of optical fibres from sources that are located in its cladding region is studied using computer simulation. The author uses a model consisting of a light-collecting fiber with sources in its cladding which is connected to an `attached fiber´ with fixed numerical aperture that guides the collected light to a detector. He considers light injection into positively guiding fibers as well as leaky fibers and concludes that positively guiding fibers if they are made long enough, can collect more light than leaky fibers. The injection efficiency of positively guiding fibers increases linearly (on average) with increasing V-number for sources distributed homogeneously throughout the volume of the cladding, while the increase is parabolic for sources located at the core-cladding boundary. In the case of leaky fibers it is found that the injection efficiency peaks if core and cladding of the light-collecting fiber are identical