Fiber Optic Wiki

Multimode Step Index

August 25, 2011

Consider the illustration in Figure 3-8. This diagram corresponds to multimode propagation with a refractive index profile that is called step index. As you can see, the diameter of the core is fairly large relative to the cladding.

Multimode Step Index Of Fiber-Optical

August 25, 2011

The illustration also shows the input pulse and the resulting output pulse. Note that the output pulse is significantly attenuated relative to the input pulse. It also suffers significant time dispersion. The reasons for this are as follows.

Single-Mode Step Index

August 25, 2011

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.

Modes Step Index

August 25, 2011

Consequently, extremely little or no energy is lost to heat through the leakage of the higher modes into the cladding, because they are not present. All energy is confined to this single, lowest-order mode. Because the higher-order mode energy is not lost, attenuation is not significant. Also, because the input signal is confined to a single ray path, that of the lowest-order mode, very little chromatic dispersion occurs.

Single-Mode Dual-Step Index

August 25, 2011

These fibers are single-mode and have a dual cladding. Depressed-clad fiber is also known as doubly clad fiber. Figure 3-10 corresponds to single-mode propagation with a refractive index profile that is called dual-step index.

Plastic-Clad Silica (PCS) Fiber-Optic Cable

August 24, 2011

The attenuation of PCS fiber-optic cable falls between that of glass and plastic. PCS fiber-optic cable has a glass core, which is often vitreous silica, and the cladding is plastic, usually a silicone elastomer with a lower refractive index.

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