Specialty Optical Fibers Handbook

intensity. For example, if a lower output divergence (smaller spot size) than the

fiber normally exhibits is desired, an up-taper (Fig. 18.7) can be used.

Alternately, if a larger divergence is required, a down-taper (Fig. 18.8) can be

used.

In situations in which it is desirable for the optical power to spill out of the

fiber abruptly at a spot size larger than the fiber NA alone can attain, but there is

only a short distance to the target (such as a laser scalpel), a very short taper

length can be used. This decreases the output spot size versus the design shown in

Fig. 18.9, and thereby increasing the power density of the spot. In addition, the