Illumination offset beam

Fig. 20-2 (a) Coordinates for describing the fields of the beam incident on the endface and (b) the fraction of total power of a Gaussian beam entering the modes of an infinite parabolic-profile fiber as a function of the tilt angle 0.. The orientation of the Gaussian beam is shown for (c) on-axis, (d) tilted and (e) offset illumination. 

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