Single-Mode Step Index

Single-mode propagation is illustrated in Figure 3-9. This diagram corresponds to single-mode propagation with a refractive index profile that is called step index.

As the figure shows, the diameter of the core is fairly small relative to the cladding. Because of this, when light enters the fiber-optic cable on the left, it propagates down toward the right in just a single ray, a single mode, which is the lowest-order mode. In extremely simple terms, this lowest-order mode is confined to a thin cylinder around the axis of the core. The higher-order modes are absent.

August 25, 2011

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