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Semiconductor optical amplifiers (SOAs) can be used as linear in-line amplifiers for extended-reach passive optical
networks, or as gain/phase-switchable devices. For these applications, gain, bandwidth and saturation power are
important. The saturation power can be increased by decreasing the confinement factor and by increasing the length such
that the overall gain remains constant. In this paper we investigate the saturation characteristics of 1.55μm InGaAsP-InP
bulk SOA. We do so by using the physically based simulation tool ATLAS.
The simulation tool ATLAS supports simulation of semiconductor lasers only, however making the mirror reflectivities
small, the lasing threshold is increased such that lasers are essentially reduced to amplifiers. Next, for investigating the
saturation characteristics of SOA, the amplifier gain should be influenced by injecting an optical light power. However,
ATLAS cannot simulate the required source directly. Instead, we use in the electron rate equation simultaneously two
competing independent models for spontaneous radiative recombination, namely the so-called general model (total
recombination rate BnT p with bimolecular recombination coefficient B, electron and hole concentrations nT and p) and
the standard model for recombination due to amplified spontaneous emission into the mode under consideration
(determined by the product of Fermi functions for electrons and holes). In the photon rate equation, only the standard
model is used. We then increase B, and thus simulate a decrease of the carrier concentration that would physically result
from an external optical signal. We show that under conditions of constant injection current and device length an n-doping
(p-doping) of the active layer increases (decreases) the input saturation power. In addition we observe that for
constant injection current and amplifier gain, a p-doping (n-doping) of the active layer increases (decreases) both the
input and output saturation powers because of an reduced (slightly increased) Auger-dominated carrier lifetime.
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