The primary difference between this work and previous studies is that the dispersive nature of core and cladding materials is taken into consideration. When plotted on a graph as a function of distance from the center of the fiber, the index of refraction resembles a step function. Graded index fiber is a type of fiber where the refractive index of the core is lower toward the outside of the fiber. For a short fiber, the graded index fiber has a larger splicing tolerance to misalignment than the step index fiber. For a gradedindex fiber, if we draw the refractive index from the cladding region to the core. Single mode and multimode fibers can have a step index or graded index refractive index profile. Types of optical fiber learning outcome epg pathshala. Other articles where gradedindex fiber is discussed. For various reasons, superior performance can be obtained from a gradedindex fibre, in which the glass composition, and hence the refractive indices, change progressively, without abrupt transition, between the core and the outer diameter. Field properties for a realistic fiber the solution method described in secs.
In graded index fibers, the refractive index of the core varies gradually as a function of radial distance from the fiber center. In fiber optics, a graded index is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the optical axis of the fiber because parts of the core closer to the fiber axis have a higher refractive index than the parts near the cladding, light rays follow sinusoidal paths down the fiber. The question then arises as on how to compute the other. Pdf on the determination of the refractive index of a fibre. Step index optical fiber multi mode and single mode step index fibers hd duration. Another type of fibre, known as singlemode sm fibre, eliminates multimode dispersion by reducing the diameter of the core. It is quite common to identify the first type of fiber as pof and the second one as pfpof made of perfluorinated material or gipof, however in the following, for sake of clarity, pmmasipof will be used to address large core step index fibers. Within the multimode fiber choices, the degree of refraction change between the core and the cladding varies between graded index and step index. Step index fiber and graded index fiber, step graded index. The main characteristics of step index single mode optical fibers are as follows. Jul 16, 2016 as noted before, multimode fiber may be divided into step index and graded index fiber.
Gradedindex multimode optical fibers, optimized for signal transmission at 850 and. The following illustration shows the differences between these two types of multimode fibers on refractive index profile a. Business units fiber optics stepindex multimode fibers with a fused silica core are the material of choice for laser beam transmission. Many multimode fibers are socalled stepindex fibers, where the refractive index is. Modes of optical fibers singlemode and multimode fiber. Guide modes of stepindex and other fibers can be calculated and optimized with the rp fiber power software. Thorlabs gradedindex grin multimode fiber provides lower modal dispersion and less bend loss than traditional multimode stepindex fiber, with a broad operating wavelength range from 800 1600 nm see the graphs tab for attenuation plots over. A typical design of a gradedindex fiber contains a parabolic profile from the. The valuescharts in this document are for polymer coated fibers only.
As noted before, multimode fiber may be divided into stepindex and gradedindex fiber. The various modes include multimode step index, singlemode step index, singlemode dual step index, and multimode graded index. Gradedindex multimode optical fibers, optimized for signal transmission at 850 and 0 nm, are available with 50125, 62. The minimum spatial bandwidth for g required to accommodate the steadystate field is thus defined by the relations nir i kmax akaxi k sin 0max. This page describes single mode step index fiber and multimode graded index fiber. Rp photonics encyclopedia gradedindex fibers, parabolic. 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.
Propagation modes fiberoptic technologies cisco press. Figure 32 shows the refractive index profile nr for this type of fiber. So graded index fiber was invented so that all the eigenmodes have nearly the same propagation time. Having a basic understanding of the guiding properties of optical fibers. 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 and step or abrupt change in refractive index takes place at the interface of core and cladding in step index fibres. N 1 is the group index in the fiber core and l is the fiber length. One mode travels straight down the center of the core. Rp photonics encyclopedia stepindex fibers, optical. When plotted on a graph as a function of distance from the center of the fiber, the index of refraction resembles a stepfunction.
Osa pulse broadening in gradedindex optical fibers. Geometricaloptics description of stepindex and gradedindex. Ii and iii has been applied to the corning 1151 fiber, which has a. Step index fibers obtain their name from this abrupt change called the step change in refractive index. Nov 11, 2017 step index optical fiber multi mode and single mode step index fibers hd duration. In a gradedindex fiber the velocity increases with distance from the core axis since the refractive index decreases.
What is the difference between step index and graded index. The software rp fiber power can be used for calculations and simulations on gradedindex fibers, e. A cladding of slightly lower refractive index n2 surrounds the core. Fimmwave will generate a continuously varying profile with an advanced spline fitting, shown below in the case of a graded core fibre with a uniform cladding. With product ranges available offering polarization maintaining, bendinsensitive, rareearth doped, claddingpump and. Step index and graded index fiber free download as powerpoint presentation. In gradedindex fibers, the refractive index of the core varies gradually as a function of radial distance from the fiber center. A multimode fiber with a core refractive index of 1. Taking advantage of the durability and toughness of hcs optical fibers, these tightbuffer cables surround the fiber with highstrength aramid yarn and.
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 the case of graded index fiber grin fiber the refractive index of the core varies parabolically from the. Gradedindex fibers simulations on gradedindex fibers. Stepindex fibers obtain their name from this abrupt change called the step change in refractive index. Step index pof with large core and graded index pof. The low oh content and the uniform refractive index guarantees low beam distortion and low absorption in the visir. 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 such applications, fibers with much larger core diameters of e. 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.
Multimode fiber and multimode fiber optic cable tutorial. The step index profile corresponds to a powerlaw index profile with the profile parameter approaching infinity. Optical fiber properties core and cladding materials are selected not only on the basis of their refractive. The refractive index of core is nonuniform, the refractive index of core decreases parabolically from the axis of the fiber to its surface. The light propagation is mainly by meridonial rays. For simpler cases, the rp fiber calculator software is sufficient. Graded index fiber is of only of one type that is multi mode fiber. Together these features create a fiber well suited for a wide variety of medical and industrial applications. Thorlabs gradedindex grin multimode fiber provides lower modal dispersion and less bend loss than traditional multimode stepindex fiber, with a broad operating wavelength range from 800 1600 nm see the graphs tab for attenuation plots over this range. The stepindex profile corresponds to a powerlaw index profile with the profile parameter approaching infinity. Fibers that carry more than one mode are called multimode fibers.
Pdf on the determination of the refractive index of a. Intermodal pulse dispersion in multimode optical fibres. Both step and graded index fibers are termed as multimode fibers. Fiberguides metazlied coatings increase the attenuation of the fiber. For a short fiber, the gradedindex fiber has a larger splicing tolerance to misalignment than the stepindex fiber. Another type of fibre, known as singlemode sm fibre, eliminates multimode dispersion by reducing the diameter of the. Initial electric field is gaussian with width 10 microns. Stepindex fiber is a fiber with a uniform refractive index in its core that is a step below the refractive index of the cladding. Air serves as the cladding in the simple glass tube example. A second mode travels at a steep angle and bounces back and forth by total internal reflection. Rp photonics encyclopedia stepindex fibers, optical fiber. This video also covers the basic concepts, structure and working of step index and graded index optical fiber. A multimode stepindex fiber has a core of radius a and a constant refractive index n1.
Difference between step index fiber and graded index fiber. With product ranges available offering polarization maintaining, bendinsensitive, rareearth doped, claddingpump and photosensitive fibers. Silica core silica clad polymer or metal coated trade name. One type is stepindex multimode fiber and the other type is gradedindex multimode fiber. How can i propagate a continuous gaussian electric field. Third type optical fiber is called singlemode fiber in which light travels largely parallel to the fiber axis with little distortion of the digital light pulse.
Stepindex fibers have a uniform core with one index of refraction, and a uniform cladding with a smaller index of refraction. The refractive index of core is nonuniform, the refractive index of core decreases parabolically from the axis of the fibre to its surface. Intermodal pulse dispersion in multimode optical fibres and. Both step and graded index fibers are termed as multi mode. It is used for shorter distances at very low pulse frequencies. In a graded index fiber the velocity increases with distance from the core axis since the refractive index decreases.
Gradedindex fibers are not only used for telecom purposes, but also e. Multimode graded index fiber graded index fiber is a type of fiber where the refractive index of the core is. The refractive index variations lens corrector operator must have tried to contain it inside the core of the fiber, but i couldnt see that effect. The step index profile is used in most singlemode fibers and some multimode fibers.
If we look at the profile drawn from the measured data of a step index fiber, it looks like a step up and step down on a staircase as shown below. The optical properties of the fiber material which is usually. Suitable for light wave communication links and local area networks carrying voice, video and data. For an optical fiber, a stepindex profile is a refractive index profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the corecladding interface so that the cladding is of a lower refractive index. Jul 30, 2012 step index optical fiber in step index optical fiber, the diameter of the core is high therefore more number of modes of propagation of light can be possible. Considerable insight in the guiding properties of optical fibers can be gained by using a ray picture.
With over 30 years experience of the specialty optical fiber industry, fibercore ltd, the world leader in its field, is exclusively dedicated to the design, manufacture and commercialization of specialty fibers. Single mode and multimode fibers can have a stepindex or gradedindex refractive index profile. Step index optical fiber core radius is 40 microns. This limits the transmission rate to about 20 to 100mbits on a 1km fiber length. In comparison to allsilica fiber, where the cladding is also made of silica giving a closer index of refraction match and thus a graded index profile. The core and cladding of an optical fiber are made from the same materiala type of. Stepindex pmma fibers and their applications intechopen. For a graded index fiber, if we draw the refractive index from the cladding region to the core. If you recall, there are two types of multimode fiber. Fimmwave will generate a continuously varying profile with an advanced spline fitting, shown below in the case of a gradedcore fibre with a uniform cladding. 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.
Gradedindex gi fibre reduces multimode dispersion by grading the refractive index of the core so that it smoothly tapers between the core centre and the cladding. The various modes include multimode step index, singlemode step index, singlemode dualstep index, and multimode graded index. A multimode step index fiber has a core of radius a and a constant refractive index n1. For simpler cases, the rp fiber calculator software is sufficient definition.
For a lplpwave with the circumferential order lfor. The refractive index of the core of the step index fiber is constant through out the core. It compares both step index and graded index fibers. Single mode or monomode step index fiber allows the propagation of only. The most common refractive index profile for a gradedindex. It bends the rays inward and also allows them to travel faster in the. There are two methods to classify fiber optic cables. Guide modes of step index and other fibers can be calculated and optimized with the rp fiber power software. Based on above, there are three types of fiber optic cable.