Difference between step index fiber and graded index fiber. An explanation of srs beam cleanup in gradedindex fibers and. A stepindex fiber is characterized by the core and cladding refractive indices n 1 and n 2 and the core and cladding radii a and b. These fibers are available with acrylate coatings and also high performance polyimide, aluminum, and gold coatings that allow. Spatiotemporal evolutions of similariton pulses in.
Graded index or step index multimode fiber fiber optic. Geometry of an optical fiber, showing core, cladding, and jacket. Gipofs offer a direct replacement and a low cost alternative to traditional glass. As a result, graded index fibers have bandwidths which are significantly greater than step index fibers, but still much lower than singlemode fibers. For linearly polarized waves in graded index fibers the scalar wave equation is effective. This page describes single mode step index fiber and multimode graded index fiber. Step index plastic optical fiber perfluorinated gradedindex polymer optical fibers gipofs combine high data transmission rates and low attenuation in the commercially desirable 8500nm range. It is customary in the theory of optical fibers to make the weakly guiding approximation n. They get their name from the step shaped refractive index profile between the fiber core and fiber cladding. 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. From the example studied before, we have a 10km graded index fiber with a core. A multimode graded index fiber with a parabolic index profile core is illustrated in figure 12. It bends the rays inward and also allows them to travel faster in the. Pure fused silica step index multimode fibers simm, opti mised for applications in the uvvis and visir wavelengths.
The number of modes in the fiber is about half that of. Mode competition in a gradedindex fiber favors the lp01 stokes mode while. Fiberguides agi fibers feature a graded index profile instead of a step index profile. 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 fibers, advantages and disadvantages 1. Rp photonics encyclopedia v number, normalized frequency. Beam cleanup via stimulated raman scattering in multimode fibers is modeled by numerically considering the competition between the stokes modes of graded index and step index fibers. Gold coatings not only enable the fiber to perform in challenging applications, but also in a wider temperature range than conventional polymer coatings. The step index profile is used in most singlemode fibers and some multimode fibers.
When plotted on a graph as a function of distance from the center of the fiber, the index of refraction resembles a step function. Gaussian approximation of the fundamental modes of graded. Multimode step index fibers multimode graded index fibers. A multimode fiber where the core is all the same index of refraction. Modal dispersion can be further decreased by selecting a smaller core size less than 510. Direct numerical integration of the wave equation is used to establish the validity of approximating the fundamental mode of gradedindex fibers by a gaussian function. The refractive index of the core of the step index fiber is constant through out the core. It simplifies the characteristic equation for the modes. Graded index or step index multimode fiber fiber optic solution. The parabolic graded index fibers were also analyzed. In a graded index fiber the velocity increases with distance from the core axis since the refractive index decreases.
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. This indicates that in step index, core and cladding have their own constant index of refractions n1 and n2 respectively. Step index and graded index fiber optical fiber refractive index. Structure, basics and types of optical fibers step index. Schematic diagram showing a multimode step index fiber, multimode graded index and single mode step index fiber, and the pulse broadening due to intermodal. Multimode fibers may be constructed with either graded or stepindex profile. Air serves as the cladding in the simple glass tube example. The refractive indices in the core and cladding are constant.
Pdf equilibrium modal power distribution measurement of. Spatiotemporal evolutions of similariton pulses in multimode. The results showed that the similariton pulses can be generated in both multimode fibers. The stepindex profile corresponds to a powerlaw index profile with the profile parameter approaching infinity. 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. As we have discussed in the earlier article about the light propagation through an optical fiber after total internal reflection. Graded index fiber in step index fiber, core has the constant refractive index n2 as shown in figure 7a. Stepindex fibers obtain their name from this abrupt change called the step. In this video, i have covered optical fibers with following outlines. The advantage of the multimode graded index compared to the multimode step index is the considerable decrease in modal dispersion. Step index fibers obtain their name from this abrupt change called the step. In step index fibers, sudden step change takes place in the refractive index at the corecladding interface.
In a graded index fiber the velocity increases with distance from the core. Suitable for light wave communication links and local area networks carrying voice, video and data. While in case of graded index fibers, refractive index of the core is nonuniform. The refractive index of the core is uniform and step or. Structure, basics and types of optical fibers step index and. Index of refraction is maximum at the center of the core. What is the difference between step index and graded index. Some popular fiber sizes the transition of the optical parameters from the core to the cladding can be discontinuous stepindex fiber or smooth gradedindex fiber.
Beam cleanup via stimulated raman scattering in multimode fibers is modeled by numerically considering the competition between the stokes modes of gradedindex and stepindex fibers. Step index multimode optical fibers newport corporation. Jan 22, 2019 in this video, i have covered optical fibers with following outlines. Graded index optical fiber in step index optical fiber. Stepindex fibers are used for the transmission of laser power in sensor technology, for industrial applications, and in medical technology. Stepindex fibers have a uniform core with one index of refraction, and a uniform cladding with a smaller index of refraction. There are two types of optical fibers depending on the refractive index of core and cladding are available. Step index and graded index fiber free download as powerpoint presentation. It compares both step index and graded index fibers.
Multi mode graded index n 1 n 2 the graded index reduces modal dispersing to 1nskm or less. Aluminum coatings not only enable the fiber to be used in applications of a wider temperature range, but also offers excellent protection at extended stress levels. A multimode or singlemode optical fiber with a uniform refractive index throughout the core. The refractive index of core is nonuniform, the refractive index of core decreases parabolically from the axis of the fiber to its surface. At the core cladding interface there is sudden decrease in the refractive index from n2 to n1. Graded index fiber based on the number of modes of transmission, optical fibers are classified into two categories i. The paper presents and compares the far field modal power distributions for i 2 km and 3 km stepindex multimode hard plastic cladding fibers, hpcf, simmf with 200 m silica core diameter, 0. Typical core diameters of gradedindex fibers are 50, 62. We present numerically these issues in a graded index and step index multimode fibers and provide a first look at the complex spatiotemporal dynamics of similariton pulses. These fibers are primarily used in data transmission applications where more bandwidth is needed than step index fibers can offer.
The v number is a dimensionless parameter which is often used in the context of stepindex fibers. Mode competition in a graded index fiber favors the lp01 stokes mode while mode. Step index means sharp step in the index of refraction between core and cladding interface. When plotted on a graph as a function of distance from the center of the fiber, the index of refraction resembles a stepfunction. They get their name from the stepshaped refractiveindex profile between the fiber core and fiber cladding. For singlemode fibers, that fraction is low for low v values e. The step index cable cross section is depicted in the figure2. Based on the refractive index of core medium, optical fibers are classified into two categories. The fiber is used in applications requiring a wide bandwidth and low model dispersion. Some popular fiber sizes the transition of the optical parameters from the core to the cladding can be discontinuous step index fiber or smooth graded 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. Firstly an xdirection linearly polarized wave of the form is assumed.
The v number determines the fraction of the optical power in a certain mode which is confined to the fiber core. Gradedindex multimode optical fibers, optimized for signal transmission at 850 and 0 nm, are available with 50125, 62. Fiber optics gradedindex polymer optical fiber gipof. Multimode optical fiber can be built with either graded index or step index. The refractive index profile and ray transmission in a multimode graded index fiber. It leads to the concept of linearly polarized modes. Types of optical fiber learning outcome epg pathshala. Based on above, there are three types of fiber optic cable. Optical fibers are classified into two types based on the refractive index profile of core and cladding. Jul 16, 2016 as a result, gradedindex fibers have bandwidths which are significantly greater than stepindex fibers, but still much lower than singlemode fibers. In a gradedindex fiber the velocity increases with distance from the core. Graded index fiber is a type of fiber where the refractive index of the core is lower toward the outside of the fiber. It is maximum at the core axis and then it decreases generally parabolically with increasing distance from the core axis.
In addition, multimode fibers are described using a system of classification determined by the iso 11801 standard om1, om2, and om3 which is based on the modal bandwidth of the multimode fiber. Number of modes for step index fiber n v 2 2, where v is cut off frequency or normalized frequency or v number. We show that the fundamental modes of fibers, whose index profile can be expressed as a power law, are indeed very nearly gaussian in shape that is probably also true for gradedindex fibers with convex profiles other than a. Graded index fiber is of only of one type that is multi mode fiber. The path followed by the light in a fiber is called the mode. For a stepindex 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. An explanation of srs beam cleanup in gradedindex fibers. As a result, gradedindex fibers have bandwidths which are significantly greater than stepindex fibers, but still much lower than singlemode fibers. 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. Graded index fiber single mode step index fiber 125 micron. The step index profile corresponds to a powerlaw index profile with the profile parameter approaching infinity. There are two methods to classify fiber optic cables. The most common refractive index profile for a graded index.
It remains constant throughout the cladding part of optical fiber. The stepindex profile is used in most singlemode fibers and some multimode fibers. Optical fibers are therefore classified as stepindex or gradedindex, and multimode or singlemode, as illustrated in fig. These fibers are available with acrylate coatings and also high performance. The refractive index of the core of the graded index fiber is maximum at the center of the core and then it decreases towards corecladding interface. Pdf design of mode scramblers for stepindex and graded.
Step index fibers have a uniform core with one index of refraction, and a uniform cladding with a smaller index of refraction. Multimode stepindex fibers multimode gradedindex fibers. Pdf design of mode scramblers for stepindex and gradedindex. So graded index fiber was invented so that all the eigenmodes have nearly the same propagation time. Jul 16, 2016 as a result, graded index fibers have bandwidths which are significantly greater than step index fibers, but still much lower than singlemode fibers. Design of mode scramblers for stepindex and gradedindex plastic optical fibers article pdf available in journal of lightwave technology 233. Stepindex pmma fibers and their applications intechopen. The step is the shift between the core and the cladding, which has a lower refractive index. The refractive index of core is nonuniform, the refractive index of core decreases parabolically from the axis of the fibre to its surface. Comparative investigation of graded index optical fiber. In multimode step index fiber core refractive index is constant therefore all modes have same velocity but. 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.
Classification of optical fibers step index graded index. Pdf effects of graded order on the characteristics of the. Sep 03, 2011 the refractive index of the core of the graded index fiber is maximum at the center of the core and then it decreases towards corecladding interface. Pdf the properties of modes that propagate through the step index fiber were perfectly analyzed. We present numerically these issues in a gradedindex and stepindex multimode fibers and provide a first look at the complex spatiotemporal dynamics of similariton pulses. The main application for gradedindex fibers is in mediumrange communications, such as local area networks. Sep 19, 2015 there are two types of optical fibers depending on the refractive index of core and cladding are available. M u l t i m o d e s t e p i n d ex f i b r graded index fiber single mode step index fiber a b c 10 gm 125 gm. Compare the numerical apertures na of a stepindex fiber with n11. Index of refraction is constant for cladding part of the fiber. The relative gain of each stokes mode is calculated by considering the overlap the various pump and stokes modes of the fibers. Step index fibers are used for the transmission of laser power in sensor technology, for industrial applications, and in medical technology. Within the multimode fiber choices, the degree of refraction change between the core and the cladding varies between graded index and step index.