As we have discussed in the earlier article about the light propagation through an optical fiber after total internal reflection. If this were a multimode step index fiber with the same n1 and n2, then the full dispersion total spread would roughly be 6. We choose step index optical fibers, because amongst all the other refractive index profiles that step index profile is very simple refractive index profile, which can. The question then arises as on how to compute the other. Graded index multimode fibre contains a core in which the refractive index diminishes gradually from the center axis out toward the cladding. Multimode fiber is rarely available longer than couple km and is used to connect server to a network backbone.
A multimode or singlemode optical fiber with a uniform refractive index throughout the core. Step index fiber is a fiber in which the core is of a uniform refractive index and there is a sharp decrease in the index of refraction at the cladding. The refractive index of the core is uniform while in case of graded index fibers, refractive index of the core is nonuniform. The cutoff angle for light entering the fiber from air is found to be 8. The fiber can use either led or laser light sources. When plotted on a graph as a function of distance from the center of the fiber, the index of refraction resembles a step function. In the case of graded index fiber, the refractive index of a core is a constant and is larger than the refractive index of the cladding. The higher refractive index at the center makes the light rays moving down the axis advance more slowly than those near the cladding. Step index and graded index fiber mode of the fiber. For a lplpwave with the circumferential order lfor.
The path followed by the light in a fiber is called the mode of the fiber. In the figure shown below you can see graded index fiber with its index profile. If the refractive index of the core in a fiber is uniform throughout and undergoes abrupt change or step at the cladding boundary, it is called step index fiber. Optical fibers are classified into two types based on the refractive index profile of core and cladding. The light propagation is mainly by meridional rays. In the case of graded index fiber grin fiber the refractive index of the core varies parabolically from the. Step index and graded index fiber free download as powerpoint presentation. This page describes single mode step index fiber and multimode graded index fiber. The refractive index of core is nonuniform, the refractive index of core decreases parabolically from the axis of the fibre to its surface. Differentiate between step index and graded index fibre. The number of modes in the fiber is about half that of step index fiber having the same diameter.
Describe multimode and single mode step index and graded index fibers. The termination is achieved in a fast and easy way, independent of material. A multimode fiber where the core is all the same index of refraction. Because parts of the core closer to the fiber axis have a higher refractive index than the parts near the cladding.
Smooth end face termination of microstructured, graded. Graded index fiber is a type of fiber where the refractive index of the core is lower toward the outside of the fiber. Consider two dielectric media with different refractive indices and with n 1 n 2 and that are in perfect contact, as shown in figure 5. If the refractive index of the core in a fiber is made to vary as a function of the. The refractive index of the core is uniform and step or abrupt change in refractive index takes place at the interface of core and cladding in step index fibres. Intermodal pulse dispersion in multimode optical fibres. An accurate numerical method is described for solving the helmholtz equation for a general class of optical fibers.
Step index and graded index fibre comparison between step index and graded index fibre optical fiber cable here is the comparison between step index and graded index fibres on the basis of various parameters like basic structure, working principle, types, refractive index profile, propagation of light inside fibers, dispersion in optical. In multimode light follows multiple paths through the fiber core. In graded index, index of refraction is not constant but vary smoothly across the diameter of the core. Thereby allowing propagation of ray in a curved path. As noted before, multimode fiber may be divided into step index and graded index fiber. These fibers may have an arbitrary number of concentric circular layers. One mode travels straight down the center of the core. In step index fibers, sudden step change takes place in the refractive index at the corecladding interface.
Step index plastic optical fiber perfluorinated graded index polymer optical fibers gipofs combine high data transmission rates and low attenuation in the commercially desirable 8500nm range. Stepindex fibers have a uniform core with one index of refraction, and a uniform cladding with a smaller index of refraction. Identify the two basic types of single mode step index fibers. Step index, graded index become focus for plastic optical fiber applications. The method yields detailed information about the spatial and angular properties of. The basic law of light guidance is snells law figure 5. This paper reports on some theoretical and experimental investigations of the radial refractive index gradient that maximizes the informationcarrying capacity of a multimode optical waveguide.
For a step index fiber both single mode and multimode optical fibers, the refractive index of the core is uniform throughout the cladding region and undergoes an abrupt change at the corecladding boundary. Since the diameter of the multimode step index fiber is large 50 micrometre, therefore it can support multiple modes of light. This video is about step index and graded index fiber. At the core cladding interface there is sudden decrease in the refractive index from n2 to n1. Difference between step index fiber and graded index fiber. Multimode step index fibers multimode graded index fibers. The refractive index of the core is uniform throughout and undergoes on abrupt change at the core cladding boundary. In this type of fiber, the light ray experiences refraction thus gets bent towards the core. The most common refractive index profile for a gradedindex fiber is very nearly parabolic. Here you will know the list of differences between step index fiber and graded index fiber. This video also covers the basic concepts, structure and working of step index and graded index optical fiber. Graded index fiber is another type of optical fiber in which the refractive index of the core is nonuniform. The fiber is used in applications requiring a wide bandwidth and low model dispersion. Rp photonics encyclopedia stepindex fibers, optical.
The refractive index of the core of the step index fiber is constant through out the core. The stepindex profile corresponds to a powerlaw index profile with the profile parameter approaching infinity. Difference between step index fiber and graded index fiber brainkart. There are two methods to classify fiber optic cables. A step index fiber is characterized by the core and cladding refractive indices n 1 and n 2 and the core and cladding radii a and b. Fiber optics gradedindex polymer optical fiber gipof. As you can see in the image above, that refractive index of. Upon completion of this chapter, you should be able to do the following. If you recall, there are two types of multimode fiber. Step index and graded index fiber optical fiber refractive index. Difference between step index fiber and graded index fiber with. Within the multimode fiber choices, the degree of refraction change between the core and the cladding varies between graded index and step index. Explain the terms refractive index profile, relative refractive index difference, and profile parameter.
The parabolic profile results in continual refocusing of the rays in the core, and minimizes modal dispersion. In 1966, the first plastic optical fiber pof product with a polymethyl methacrylate or acrylic core was introduced by dupont under the brand name crofon. In a graded index fiber the velocity increases with distance from the core axis since the refractive index decreases. The advantage of the multimode graded index compared to the. This nonuniformity is present because the refractive index is higher at the axis of the core and continuously reduces. Unlike graded index optical fiber, the step index fiber has a constant refractive index at the core as well as cladding. Therefore it is known as multimode step index fiber. This article will compare graded index multimode fiber. A step index fiber has a core index of refraction of n 1 1. Multimode optical fiber can be built with either graded index or step index. Air serves as the cladding in the simple glass tube example.
Step index and graded index fiber step index fiber. Graded index porous optical fibers dispersion management in. It remains constant throughout the cladding part of optical fiber. For step index fiber, the refractive index of the core is uniform and step or abrupt change in refractive index takes place at the interface of core and cladding in step index fibers. In this video you will learn the basics of step index fiber and graded index fiber. Optical fibres can be categorised into two types on the basis of refractive index profile in. It compares both step index and graded index fibers. For a value of a 2, the number of guided modes 2 in a graded index fibre is only half the modes in a step index fibre wi th the sam values of a and core diameter. For simpler cases, the rp fiber calculator software is sufficient definition. What is the difference between step index and graded index. Step index and graded index fiber step index vs graded. The stepindex profile is used in most singlemode fibers and some multimode fibers.
The step is the shift between the core and the cladding, which has a lower refractive index. A second mode travels at a steep angle and bounces back and forth by total internal reflection. The light propagation is mainly by meridonial rays. D fiber which has a step index refractive index profile. Each layer is described by an outer diameter and the real and imaginary parts of the refractive index. The crosssectional shape of the fibers is preserved, and the structure in microstructured plastic optical fibers pofs is of good quality, showing no plastic deformations. The app can be used for analyzing both step index fibers and graded index fibers.
It bends the rays inward and also allows them to travel faster in the. Types of optical fiber learning outcome epg pathshala. Graded index or step index multimode fiber fiber optic. Guide modes of stepindex and other fibers can be calculated and optimized with the rp fiber power software. In a gradedindex fiber the velocity increases with distance from the core. Graded index fiber is of only of one type that is multi mode fiber. Step index fibers obtain their name from this abrupt change called the step. The main difference in step index and graded index fibers lies in the following points.
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