signal degradation

Download Signal degradation

Post on 25-May-2015




1 download

Embed Size (px)



2. SIGNAL DEGRADATION Signal attenuation determines the maximum unamplified or reapeaterless separation between a transmitter and a receiver. Thedegree of attenuation has large influence on system cost. 3. Signaldistortion in fiber cause signal pulses tobroaden as they travel along a fiber . This will lead to overlapping in pulses and geterrors in output. It limits the information carrying capacity offiber. 4. ATTENUATIONAttenuation in fiber optics, also known astransmission loss. It is the reduction in intensity of light the lightbeam with respect to distance traveledthrough a transmission medium. Attenuation coefficients in fiber opticsusually use units of dB/km through themedium. 5. . Themedium is usually a fiber of silica glass that confines the incident light beam to the inside. Attenuation is an important factor limiting the transmission of a digital signal across large distances. Attenuation in optical fiber is caused primarily by both scattering and absorption 6. SCATTERING Lightscattering depends on the wavelength ofthe light being scattered. Attenuation results from the incoherent scattering of light at internal surfaces and interfaces the scattering of light in optical quality glassfiber is caused by molecular level irregularitiesin the glass structure. 7. a glass is simply the limiting case of apolycrystalline solid.ithin this framework, "domains" exhibitingvarious degrees of short-range order becomethe building blocks of both metals and alloys, aswell as glasses and ceramics.istributed both between and within thesedomains are micro-structural defects which willprovide the most ideal locations for the 8. ABSORPTION Absorption caused by three mechanisms. Absorptionby atomic defects in glasscomposition. Extrinsic absorption by impurity atom in glassmaterial. Intrinsic absorption by basic constituentsatoms of fiber material. 9. Attenuation or signal loss can also occur due toselective absorption of specific wavelengthsPrimary material considerations include bothelectrons and molecules as follows:Atthe electronic level, it depends on whether theelectron orbitals are spaced such that they canabsorb a quantum of light (or photon) of a specificwavelength or frequency in the ultraviolet (UV) orvisible ranges. At the atomic or molecular level, it depends on thefrequencies of atomic or molecular vibrationshow close-packed its atoms or molecules are, andwhether or not the atoms or molecules exhibit long-range order. 10. The design of any optically transparent devicerequires the selection of materials based uponknowledge of its properties and limitations The lattice absorption characteristics observed atthe lower frequency regions define the long-wavelength transparency limit of the material. They are the result of the interactive couplingbetween the motions of thermally inducedvibrations of the constituent atoms and moleculesof the solid lattice and the incident light waveradiation. Hence, All materials are bounded by limiting regions ofabsorption caused by atomic and molecularvibrations (bond-stretching)in the far-infrared (>10m). 11. Multi-phononabsorption occurs when two or more phonons simultaneously interact to produce electric dipole moments with which the incident radiation may couple. These dipoles can absorb energy from the incident radiation, reaching a maximum coupling with the radiation when the frequency is equal to the fundamental vibrational mode of the molecular dipole in the far-infrared, or one of its harmonics. 12. The selective absorption of infrared light by aparticular material occurs because theselected frequency of the light wave matchesthe frequency at which the particles of thatmaterial vibrate. Reflection and transmission of light wavesoccur because the frequencies of the lightwaves do not match the natural resonantfrequencies of vibration of the objects. WhenIR light of these frequencies strikes an object,the energy is either reflected or transmitted 13. THANK YOU


View more >