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Decibel (dB)
A unit of measurement of optical power which indicates relative power. A -10 dB means a reduction in power by 10 times, -20 dB means another 10 times or 100 times overall, -30 means another 10 times or 1000 times overall and so on.
PDH
Plesiochronous Digital Hierarchy (PDH) is a transmission system for voice communication using plesiochronous synchronisation. The transmitter adds dummy information bits to allow multiple channels to be bit interleaved. The receiver discards these bits once the signals have been demultiplexed. PDH combines multiple 2 Mb/s (E1) channels in Europe and 1.544 Mb/s (DS1) channels in the US and Japan.
Spectral Width
Spectral Width is the wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This is the same convention used in bandwidth, defined as the frequency range where power drops by less than half (at most -3 dB).
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