tutorial-2 - dBm: a convenient measure of absolute power....

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dBm: a convenient measure of absolute power. To express an arbitrary power P as x dBm, or go in the other direction, the following equations could be used: where P is the power in W and x is the power measured in dBm. dB: expresses a ratio of two quantities with the same unit. If L represents the ratio of a power value P 1 to another power value P 0 , then L dB represents that ratio expressed in decibels and is calculated using the formula: P 1 and P 0 must have the same units. Rearranging the above equation gives the following formula for P 1 in terms of P 0 and L dB : As power loss can be expressed as the ratio of input power to output power, one typical use of dB is as the unit of loss. dBm cannot be used as the ratio unit and dB cannot be used as the power unit!
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Fiber attenuation: Rayleigh scattering (proportional to λ 4 ) The light with a small wavelength is difficult to thread its way through the clumps of silica molecules (diffraction) . Material absorption ( λ dependent ) Intrinsic absorption loss Extrinsic absorption loss The energy of light is transferred to the energy of atom vibration. Waveguide Imperfection
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This note was uploaded on 05/18/2010 for the course INFORMATIO IEG 4030 taught by Professor Liank.che during the Spring '10 term at CUHK.

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tutorial-2 - dBm: a convenient measure of absolute power....

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