Recommendation G.957 (06/99)
20
The interaction between the transmitter and the fibre is accounted for by a parameter epsilon. It is
defined as the product of 10
−
6
times the bit rate (in Mbit/s) times the path dispersion (in ps/nm)
times
the RMS spectral width (in nm). For a 1 dB power penalty due to dispersion,
epsilon has a maximum
value. For intersymbol interference alone, the value 0.306 is applied to LEDs and SLM lasers. The
20 dB width for SLM lasers is taken as 6.07 times the RMS width. (For L-16.2 only, it is necessary
to increase epsilon to 0.491, corresponding to a 2 dB power penalty.) For intersymbol interference
plus
mode partition noise, the maximum value 0.115 is applied to MLM lasers. (For I-1 and I-4, the
large spectral widths may not often occur, but they are retained here for possible cost savings.) For
wavelength chirp, no known value is applied to SLM lasers.
For
a particular spectral width, the optical path dispersion is fixed for a particular application code.
With the appropriate path distance from Table 1, the maximum allowed dispersion coefficient
follows. The spectral dependence of the dispersion coefficient then determines the dispersion-limited
wavelength range. (The use of the dispersion coefficient beyond the
wavelength ranges stated in
Recommendations G.652, G.653 or G.654 is for further study.)
ANNEX B
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