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320 Chapter Thirteen
Figure 13.24 Fiber optics.
The limiting resolution (in line pairs per unit length) of a coherent
fiber bundle is approximately equal to half the reciprocal of the fiber
diameter; by synchronously oscillating or scanning both ends of the
fiber, this resolution can be doubled. When the fibers are tightly
packed, their surfaces contact each other and leakage of light from one
fiber to the next will occur. Moisture, oil, or dirt on the fiber surface
can also interfere with total internal reflection. This is prevented by
coating or “cladding” each fiber with a thin layer of lower-index glass
or plastic. For example, the core glass may have n 1 1.72 and the
