Crosstalk in fiber Raman amplification for WDM systems - pdf 25

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Abstract-The crosstalk between channels in Raman amplification
for two-channel WDM system is calculated for the first time. Our the-
ory shows that the severe crosstalk may occur even in the linear am-
plification (or pump undepletion) region. To ensure small crosstalk,
the signal gain and the injected pump power should be limited to the
values well below the threshold of Raman amplification. As a numeri-
cal example, 30-dB gain penalty and 3-dB pump power penalty occur
when 30-dB signal-interference ratio (SIR) is required. The conversion
efficiency of Raman amplification in WDM systems is very low.
I. INTRODUCTION
PTICAL amplification by stimulated Raman scatter-
0 ing in a single-mode fiber is of interest for applica-
tions in optical communication systems. Gains exceeding
20 dB have been demonstrated in fibers of several kilo-
meters length [1] and the maximum unrepeatered trans-
mission length was estimated theoretically to be above 400
km [2]. One potential application is for optical amplifi-
cation in WDM systems because the bandwidth of the Ra-
man amplifiers can be large enough to accommodate two
or more WDM channels and the use of demultiplexing
and multiplexing in each repeater can be avoided. There-
fore it is important to investigate various behaviors of Ra-
man amplifiers for WDM systems. The gain limited by
spontaneous scattering has been discussed under various
channel spacing and wavelength filtering [3]. In this paper
we investigate the crosstalk between WDM channels with
external Raman amplification, because the crosstalk may
severely deteriorate the performance of WDM systems
without external Raman amplification [4]-[ 111.

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Signal light amplification by stimulated Raman scattering in an N-channel WDM optical fiber communication system
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