Leaky rays excitation

We can now calculate the source power carried by bound rays when the fiber is illuminated by the diffuse source. In this part of the chapter we determine the total source power, the total bound-ray power and the radial distribution of bound-ray power over the core cross-section. Later in the chapter we show how to derive the distribution of power among the various bound-ray directions. We assume that the source of Fig. 4-3(a) is placed against the fiber endface in Fig. 4—4, and its surface covers at least the core cross-section. Only the portion of the source within the core cross-section can excite bound rays, so we ignore any effects due to the source outside of this region. The excitation of leaky rays by sources is examined in Chapter 8. 

Only part of the total source power is transmitted to bound rays the rest excites leaky rays, which is discussed in Chapter 8. If we denote the amount of source power transmitted to all bound rays by Pj, then the source (Efficiency S is defined by... 

Outside of the circular region only leaky rays are excited, as discussed in Chapter 8. When 00 = 0 and the beam is on axis, bound rays are excited over the whole core and propagate parallel to the fiber axis. If the beam carries uniform power P per unit cross-sectional area, then the total bound-ray power and source efficiency of Eq. (4-11) are given by... 

We begin by determining the power exciting leaky rays on fibers illuminated by a diffuse source, and then show that the spatial transient is accurately and simply described in terms of a single dimensionless parameter which embraces all the physical quantities of the problem. The effect of leaky rays on pulse dispersion is also expressible in terms of this parameter. We then show how... 

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