Pdf optical solitons in gradedindex multimode fiber. The method yields detailed information about the spatial and angular properties of the propagating beam as well as the modal propagation constants for the fiber. The valuescharts in this document are for polymer coated fibers only. Their task is to slightly increase and decrease the refractive index of pure silica. A multimode stepindex fiber has a core of radius a and a constant refractive index n1. Another type of fibre, known as singlemode sm fibre, eliminates multimode dispersion by reducing the diameter of the.
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. Step index fiber in step index fibers the refractive index of the core medium is uniform and undergoes an abrupt change at the interface of core and cladding as shown in figure. The software rp fiber power can be used for calculations and simulations on gradedindex fibers, e. Gradedindex polymer optical fiber for highspeed data. Optical fibres the refractive index of the glass fibre the core must be higher than that of the plastic coating the cladding for total internal reflection to occur this type of optical fibre is called a stepindex fibre because the refractive index increases in a step from the air on the outside, to the much higher value of the cladding, to the even higher value of the core. An optical fiber that a has a uniform homogeneous isotropic refractive index core and a uniform isotropic refractive index cladding, with the core refractive index being greater than the cladding refractive index and b may have more than one cladding, each usually with a different refractive index that is lower than that of the core.
The most common core sizes for gradedindex multimode fibers are 50, 62. Both single mode and multimode optical fibers can have a stepindex or gradedindex refractive index profile. The refractive index as a function of the radius is shown in fig. Upon completion of this chapter, you should be able to do the following. 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 uniformity is present because the refractive index is higher at the axis of the core and continuously reduces with the radial movement away from the axis. Graded index fiber is a type of fiber where the refractive index of the core. A lot of this fiber transmission mode, various modes of transmission path is not the same, the time to reach the finish line after the transmission. 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. The stepindex profile corresponds to a powerlaw index profile with the profile parameter approaching infinity. An all inclusive list of the various optical fiber specification sheets. In the figure shown below you can see graded index fiber with its index profile. We show that this equation can be reduced to the standard nls equation for optical pulses whose dispersion length is much longer than the selfimaging. Guide modes of stepindex and other fibers can be calculated and optimized with the rp fiber power software. It compares both step index and graded index fibers. In the case of singlemode sm fibers and a proportion of multimode mm fibers, the fiber has a step index profile. The step index profile corresponds to a powerlaw index profile with the profile parameter approaching infinity.
Multimode fiber and multimode fiber optic cable tutorial fosco. Gradedindex multimode fibers are used for data communications and networks carrying signals moderate distances typically no more than a couple of. Thorlabs gradedindex grin patch cables are assembled with either o62. The basic material used in the manufacture of optical. For simpler cases, the rp fiber calculator software is sufficient definition. I profile and ray transmission in a multimode graded index fiber. 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. Pcvd produced multimode fibers show excellent process for gradedindex multimode fiber modal bandwidth performance.
Graded index fibre continuousindex in graded index fibre, the refractive index gradually decreases farther away from the core, hence making the boundary between cladding and core indistinct. One type is step index multimode fiber and the other type is graded index multimode fiber. Rp photonics encyclopedia stepindex fibers, optical fiber. As we know optical fiber is a very thin and flexible medium with cylindrical shape. The radial distribution of the fiber refractive index is called the index profile. This page describes single mode step index fiber and multimode graded index fiber.
The image to the right is a photograph of a stepindex fiber, shown next to the tip of a sewing needle. Graded index fiber is a type of fiber where the refractive index of the core is lower toward the outside of the fiber. In fiber optics, a graded index or gradient index fiber is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the fiber axis the imaginary central axis running down the length of the fiber. Fibers that carry more than one mode are called multimode fibers. There are two methods to classify fiber optic cables.
The higher index of refraction in the centre of the core slows the speed of some light rays, allowing all the light rays to reach the receiving end at. A typical value is an 0,2 leading to a maximum angle of incidence. Optical fiber cable chemical stripping fixture case number. This limits the transmission rate to about 20 to 100mbits on a 1km fiber length. We show that this equation can be reduced to the standard nls equation for optical pulses whose dispersion length is much longer than the selfimaging period of the. Drakaelite gradedindex multimode optical fiber prysmian group. Step index multimode optical fibers newport corporation. 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. For a graded index fiber, if we draw the refractive index from the cladding region to the core, we can see it varies gradually as a function of radial distance from the fiber center as shown in the diagram below. Within the multimode fiber choices, the degree of refraction change between the core and the cladding varies between graded index and step index.
The refractive index of the core of the step index fiber is constant through out the core. 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. Fiberguides metazlied coatings increase the attenuation of the fiber. Graded index polymer optical fiber for highspeed data communication takaaki ishigure, eisuke nihei, and yasuhiro koike we successfully obtained a highbandwidth 1 ghz km and lowloss 90 dbkm at 0. Gradedindex polymer optical fiber for highspeed data communication takaaki ishigure, eisuke nihei, and yasuhiro koike we successfully obtained a highbandwidth 1 ghz km and lowloss 90 dbkm at 0. In fiber optics, a gradedindex or gradientindex fiber is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the fiber axis the imaginary central axis running down the length of the fiber. Perfluorinated gradedindex polymer optical fibers gipofs combine high data transmission rates and low attenuation in the. Light propagation properties of graded index glass fibers. N 1 is the group index in the fiber core and l is the fiber length. Unlike graded index optical fiber, the step index fiber has a constant refractive index at the core as well as cladding.
As noted before, multimode fiber may be divided into stepindex and gradedindex fiber. Gradedindex grin multimode fiber optic patch cables. 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. Other articles where gradedindex fiber is discussed. 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. Step index fiber is not widely used only pof and pcshcs plastic or hard clad silica, plastic cladding on a glass core use a step index design today. 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. Figure 32 shows the refractive index profile nr for this type of fiber. This indicates that in step index, core and cladding have their own constant index of refractions n1 and n2 respectively. Gradedindex fibers simulations on gradedindex fibers. Gradedindex fibers are not only used for telecom purposes, but also e. It mentions step index advantages, graded index advantages, step index disadvantages and graded index disadvantages.
The main idea of those approximants is to combine ra tional functions with auxiliary functions in such a way that the singularities of the approximated function. This particular fiber is fairly large by modern standards, but it provides a nice example of the different layers in an optical fiber. Multimode fiber and multimode fiber optic cable tutorial. In the case of a slab waveguide, the transverse refractive index is called the index profile. Difference between step index fiber and graded index fiber. The most common refractive index profile for a gradedindex. Feb 07, 20 spatial mode decomposition of optical fields can facilitate the understanding and analyzing of optical beam in free space 2,3, graded index multimode fibers 4, 5, and waveguides 6.
The diameter of core is about 10micrometers in case of single mode fiber and 50 to 200 micrometers in multi mode fiber. Mar 29, 2015 graded index fibre continuous index in graded index fibre, the refractive index gradually decreases farther away from the core, hence making the boundary between cladding and core indistinct. Anhydrous graded index agi multimode download silica core silica clad polymer or metal coated fiber multimode, graded index fiberguides agi fibers feature a graded index profile instead of a step index profile. Suitable for light wave communication links and local area networks carrying voice, video and data. In graded index fibers, the refractive index of the core varies gradually as a function of radial distance from the fiber center. Graded index multimode fiber uses variations in the composition of the glass in the core to compensate for the different path lengths of the modes. These fibers are primarily used in data transmission applications where more bandwidth is needed than step index fibers can offer. 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. Stepand gradedindex fibers what is the difference faq. Anhydrous graded index agi multimode fiber fiber type. A cladding of slightly lower refractive index n2 surrounds the core. One type is stepindex multimode fiber and the other type is gradedindex multimode fiber. Gradedindex grin multimode fibers your source for fiber.
Present stateoftheart of plastic optical fiber pof. Jul 16, 2016 as noted before, multimode fiber may be divided into step index and graded index fiber. Light can pass or propagate through fiber optic media as a single instance for singlemode, or refracted instances, for multimode, as shown below comparing single mode fiber and multimode fiber. The performance of multimode graded index fibers is usually superior to multimode step index fibers.
Identify the two basic types of single mode stepindex fibers. The image to the right is a photograph of a step index fiber, shown next to the tip of a sewing needle. Both step and graded index fibers are termed as multi mode. The method is applied to a practical graded index fiber under the assumptions of both coherent and incoherent illumination. Graded index fiber is a type of optical fiber where the refractive index of the core is uniform at the center core and then it decreases towards corecladding interface. So graded index fiber was invented so that all the eigenmodes have nearly the same propagation time. A multimode step index fiber has a core of radius a and a constant refractive index n1. Graded index or step index multimode fiber fiber optic.
It bends the rays inward and also allows them to travel faster in the. In graded index, index of refraction is not constant but vary smoothly across the diameter of the core. Differentiate between step index and graded index optical. The index profile determines guiding properties of the fiber or slab waveguide. What is the difference between step index and graded index. For a gradedindex fiber, if we draw the refractive index from the cladding region to the core, we can see it varies gradually as a function of radial distance from the fiber center as shown in the diagram below. Both single mode and multimode optical fibers can have a step index or graded index refractive index profile. The problem with that kind of characterization is, that the propagation delay depends on the wavelength, the temperature and the actual light distribution in the fiber. The step index profile is used in most singlemode fibers and some multimode fibers.
Pdf fabrication of a gradedindex polymer optical fiber. The following is a short description of existing pof fiber technology. For such applications, fibers with much larger core diameters of e. Advantages disadvantages of step index,graded index fiber. The question then arises as on how to compute the other. Another type of fibre, known as singlemode sm fibre, eliminates multimode dispersion by reducing the diameter of the core. 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. Although the step index profile is mathematically very simple, it can be somewhat problematic in numerical simulations of beam propagation. Spatial mode decomposition of optical fields can facilitate the understanding and analyzing of optical beam in free space 2,3, gradedindex multimode fibers 4, 5, and waveguides 6.
In this type of fiber, the light ray experiences refraction thus gets bent towards the core. Fiber center core to the cladding refractive index of glass is mutation, only one step, so called stepindex multimode fiber, referred to as stepindex fiber, optical fiber, also known as mutations. In general, the core region has a higher index than the cladding region. Thi s is because high intermdal disper sion would limit the inforrnation carrying capacity. 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. The step index cable cross section is depicted in the figure2. Dec 15, 1978 light propagation in graded index optical fibers. Here we report the observation of optical solitons and soliton selffrequency shifting in gradedindex multimode fiber. These fibers are generally categorized by bandwidth as optical multimode om typ. Fabrication of a gradedindex polymer optical fiber preform by using a centrifugal force article pdf available in korean journal of chemical engineering 193. Both step and graded index fibers are termed as multimode fibers. Silica core silica clad polymer or metal coated trade name.
Index profile of fibers or slab waveguides optiwave. Unlike the gif625ht, this new fiber will be a step index fiber instead of a graded index fiber. Gradedindex multimode optical fibers, optimized for signal transmission at 850 and 0 nm, are available with 50125, 62. An accurate numerical method is described for solving the helmholtz equation for a general class of optical fibers. Multimode step index fiber the main difference in step index and graded index fibers lies in the following points. Explain the terms refractive index profile, relative refractive index difference, and profile parameter.
Optical fibers designed to support multiple transverse modes offer opportunities to study wave propagation in a setting that is intermediate between singlemode fiber and freespace propagation. Rp photonics encyclopedia gradedindex fibers, parabolic. The following illustration shows the differences between these two types of multimode fibers on refractive index profile a. In multimode light follows multiple paths through the fiber core. In order to achieve a step index profile, the core is typically doped with a uniform level of germanium.
1120 928 1381 759 1102 1520 287 24 75 710 699 451 1329 526 157 488 310 261 1131 1378 965 512 126 1303 1207 317 327 1246 570 634 882 507 1280 896