Optical fibres acceptance cone

Thus, it is particularly advantageous to ensure that the focal point of a Fresnel lens matches with the top of the optical fibre acceptance cone then, it becomes possible to have a maximum light concentration without loss. This configuration is shown in Fig. 21.8 (Nakamura, 1992). 

In connectors light source to optical fibre, power losses result from different space characteristics of the light source and the fibre. Each light source emits a beam in its typical shape whereas a fibre can accept only these rays within the acceptance cone. Some typical losses are presented in Figure 2. 

Figure 21.3 Acceptance cone of an optical fibre, according to (Grise and Patrick, 2002).

If a light ray enters in the acceptance cone of the optical fibre, hght propagation proceeds by total reflection (cf. Fig. 21.2). If the incidence angle is not admitted in the cone, ray propagation occurs by successive sets of refraction-reflection... 

Another solution for obtaining a greater light concentration is to enlarge the acceptance cone of the optical fibre. Thus, we increase the number of rays able to propagate without loss in the fibre. Different geometrical solutions to increase the numerical aperture of the fibre exist, shown in Fig. 21.11 (Nakamura, 1992). 

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