wavelength - Attenuation in Optical Fibres Attenuation...

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Optical Communications Systems Attenuation in Optical Fibres Attenuation in Optical Fibres y Attenuation limits the optical power which can reach the receiver, limiting the operating span of a system. y Attenuation has dropped from 20dB/Km (1973) to 0.2 dB/Km (1993) y Units of attenuation are dB/Km y Simple formula relates received power P r and transmitted power P t y There are a number of major causes of attenuation in fibre: - Absorption loss - Scattering loss - Bending loss A is attenuation in dB/km L is fibre span in km 10 10 AL t r P P = Effect of attenuation y A receiver in an optical system requires a minimum optical input power to operate with a specified error probability. y Attenuation reduces the optical power available, degrading the error probability y Most system specifications allow a maximum error probability of 1E-9 Plot of error probability versus received optical power for a 622 Mbits/sec transmission system Types of Attenuation y Absorption Loss: Caused by the fibre itself or by impurities in the fibre, such as water and metals. y Scattering Loss: Intrinsic loss mechanism caused by the interaction of photons with the glass itself. y Bending loss: Loss induced by physical stress on the fibre.
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Material Absorption Losses •Material absorption is caused by absorption of photons within the fibre. •Optical power is effectively converted to heat dissipation within the fibre. •Two types of absorption exist: •Intrinsic Absorption , caused by interaction with one or more of the components of the glass •Extrinsic Absorption , caused by impurities within the glass •Absorption may result from the photons causing transitions of electrons
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This note was uploaded on 10/18/2009 for the course EE ee321 taught by Professor Ee during the Winter '06 term at Istanbul Technical University.

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wavelength - Attenuation in Optical Fibres Attenuation...

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