Hence, based on the differences in the structure of the core, there are three main types of optical fibers. Light can pass or propagate through fiber optic media as a single transmission path for single mode or for multimode fiber. It is customary in the theory of optical fibers to make the weakly guiding approximation n. Graded index or step index multimode fiber fiber optic.
Therefore this type of step index fiber is known as single mode step index fiber. Multi mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion. Optical fibers 3 lab periods objective stripping and cleaving of optical fibers for integration into optical devices. For these reasons, multimode optical fiber systems continue to be the most cost effective fiber choice for enterprise and data center applications up to 500 600 meter range. For single mode fibers, that fraction is low for low v values e. Another way to reduce modal dispersion is to reduce the cores diameter, until the fiber only propagates one mode efficiently. As a typical example, figure portrays a cable with multiple optical fibers.
A singlemode fiber is a single glass fiber strand used to transmit a single mode or ray of light. In multi mode optic fiber cable, coretocladding diameter is about 50 or 62. Unlike a longitudinal acoustic mode with negligible transverse displacement, a sam has both considerable transverse and longitudinal displacements. It leads to the concept of linearly polarized modes.
Difference between step index fiber and graded index fiber. Osa brillouin scattering induced by shear acoustic mode. This indicates that in step index, core and cladding have their own constant index of refractions n1 and n2 respectively. The diameter of core is about 10micrometers in case of single mode fiber and 50 to 200 micrometers in multi mode fiber. Rp photonics encyclopedia v number, normalized frequency. Optical fibers are thread like structure made of glass and plastic in which light travel by total internal reflection. Cross section view of optical fiber and single fiber cable single mode sm vs. Because of this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the ability for the signal to travel further.
The macrobending induced attenuation increases as the fiber mc number increases. They work on the principle of total internal reflection. We present the mechanism of backward brillouin scattering induced by shear acoustic mode sam in a step index fiber. The bandwidth is about 50 mhz km for multimode step index fiber whereas it is more than 100 mhz km in case of single mode step index fiber. Typically customers will ask for either multimode or single mode fiber cable. In a gradedindex fiber the velocity increases with distance from the core axis since the refractive index decreases. Multimode fibers will propagate many number of modes say hundreds of modes.
Types of optical fibers physical structure of optical. Difference between single mode and multi mode fiber. This study is required for further investigation of states of polarization and analysis o f electric fie ld distribution using high frequency conditions. In single mode optic fiber cable, coretocladding diameter is about 9 microns by 125 microns. You can see the image shown above, how a single mode of light is propagating through the core of the optical fiber. For a given fiber optic cable, the number of modes that exist depends on the dimensions of the cable and the variation of the indices of refraction of both core and cladding across the cross section. The attenuation of an optical fiber is wavelength dependent. Basically optical fibers can be classified according to the number of modes they can propagate. At the extremes of the transmission curve, multiphoton absorption predominates. The single mode fiber has an exceedingly small core diameter of only 5.
Step index means sharp step in the index of refraction between core and cladding interface. Low water peak fiber lwp, that provides optimum performance in both the 10 nm 2nd window and 1550 nm 3rd window wavelength with a low dispersion in the 10 nm window. In standard step index single mode fiber, the sum of the material and waveguide dispersion is zero near 10 nm, which is called the. When the core radius of a test fiber is only a few times larger than the laser beam spot size, the reflected power distribution does not indicate the refractive index correctly. Schematics of a step index profile, b cross section view of single mode fiber. Light can pass or propagate through fiber optic media as a single instance for single mode, or refracted instances, for multi mode, as shown below comparing single mode fiber and multimode fiber. Single mode fiber single mode fiber optic cable fosco. This paper is an analysis of the propagation mode of step index fiber optic. The simplest form of an optical waveguide consists of a lightconducting. 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. Typical values range from 10 dbkm for step index fibers at 850 nm to a few tenths of a dbkm for single mode fibers at 1550 nm. Single mode fibers will propagate only the fundamental mode. In fiber optic communication, a singlemode optical fiber smf is an optical fiber designed to carry only a single mode of light the transverse mode. Single mode optical fibre for patch cord drakaelite.
Discuss in brief single mode step index fiber and multi. During the lightsound coupling process, the fundamental and highorder sams can be guided and excited, ultimately generating a. By varying the fiber s waveguide structure, the waveguide dispersion can be shifted up or down, thus changing the zerodispersion point. Singlemodefiber refractiveindex profile measurement by. Singlemode fiber features only one transmission mode. Within the multimode fiber choices, the degree of refraction change between the core and the cladding varies between graded index and step index fibers. The condition for the single mode operation is given by the v number of the fiber which is defined as. Single mode fibers in a fiber, if only one mode is transmitted through it, then it is said to be a single mode fiber. For example, the number of guided modes in a step index multimode fiber is given by v 2 2, and a step index fiber becomes single mode for a given wavelength when v fiber core radius. What is the difference between step index and graded index.
Pdf comparative study of stepindex and trenchassisted. Step index optical fiber multi mode and single mode step. Single mode cable has a much smaller core 89um than multimode cable and uses a. A typical single mode fiber may have a core radius of 3. It simplifies the characteristic equation for the modes. Within the multimode fiber choices, the degree of refraction change between the core and the cladding varies between graded index and step index. Shows bending loss at 1550 nm for bending radii of 15, 10, 7. Single mode fiber optic cable has a small diametral core that allows only one mode of light to propagate. Depending upon number of modes propagated by the fiber we have single mode and multimode step index fibers. Multi mode links can be used for data rates up to 100 gbits. We have fabricated the first single mode step index and humidity insensitive polymer optical fiber operating in the 850 nm wavelength ranges.
As mentioned in the article on the structure of optical fibers, the properties of data transmission via a fiber optic depend on the core. Because of this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the. 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. A new technique for measuring the refractive index profile of single mode fibers based on the reflection method is described, and experimental results are demonstrated. Attenuation is usually expressed in dbkm at a specific wavelength. V22, and a step index fiber becomes single mode for a given wavelength when v fiber. Of course, modal dispersion is not an issue in single mode fiber because only a single mode is propagated figure 11. An overview of macrobending and microbending of optical. Singlemode fiber is a common type of optical fiber that is used to transmit over longer distances. The step index preform is fabricated using injection molding, which is an efficient method for cost effective, flexible and fast preparation of the fiber preform. In single mode light takes single path through the fiber core.
Modes are the possible solutions of the helmholtz equation for waves, which is obtained by combining maxwells equations and the boundary conditions. It is one of the two optical fiber types, the other being multi mode fiber. Beyond the reach of multimode optical fibers, it becomes necessary to use singlemode optical fiber. In step index fiber, the refractive index of core is uniform throughout and undergoes an abrupt change step change at the core cladding interface. Measurement of the numerical aperture na of multimode fibers and of the beam profile of a single mode fiber.
Single mode stepindex polymer optical fiber for humidity. There is also the socalled marcuse equation for estimating the mode radius of a step index fiber from the v number. The various modes include multimode step index, single mode step index, single mode dual step index, and multimode graded index. Singlemode fibre optic cable single mode fibre optic cable has a small diametral core that allows only one mode of light to propagate. Step index optical fiber multi mode and single mode step index. Propagation modes fiberoptic technologies cisco press. Single mode fibers are identified by the designation os or optical single mode fiber.
582 300 1281 879 1224 966 373 1165 1307 514 1307 192 243 911 1421 482 656 703 1431 81 171 59 1314 415 1144 239 185 851 264 757 123 1266 30 1032 986 1025 471 1130 284 762