N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 5 - SONET, WDM, DWDM and B-ISDN Technologies                                                                Slide 9 of 76 _________________                                                                                  __________

                                                     Attenuation

                                                Scattering Loss

                                                Absorption Loss

                                                Connection Loss

                                                Bending Loss

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Attenuation is the loss in signal power as it travels down the fiber. Four factors affect the attenuation in a fiber: Scattering of the light signal, absorption of the light signal , signal losses of the light signal at the connections and losses of the light signal at bends in the fiber.

Scattering Loss - This loss of signal happens due to impurities in the fiber. There is a limit beyond which scattering loss in a fiber cannot be reduced.
     For light with wavelength of 0.8 micro meters is 2.9 dB/Km
     For light with wavelength of 1.3 micro meters is 0.3 dB/Km
     For light with wavelength of 1.55 micro meters is 0.15 dB/Km

Absorption Loss - This loss of signal happens in a fiber due to conversion of light into heat. It is due to imperfections in the fiber. The fiber systems are designed to minimize this loss by transmitting at 0.8, 1.3 and 1.5 mm.

Connection Loss - This loss happens at the junction. A line could be repaired many times adding to this loss. This represents a large source of signal loss in fiber optic systems.

Bending Loss - A light at the bend must travel faster on the outside of the bend to keep in phase with the rest of the wave. As the radius of the bend is decreased, a point is reached where by the light on the outside of the bend cannot travel fast enough to keep in phase with the rest of the wave and the light is lost.