Introduction: The introduction of WDM systems into metropolitan
areas poses a main challenge to address system sensitivity to channel
number reconfiguration. In fact, channel add=drop may introduce a
strong variation in the operation point of the optical amplifiers (OAs)
and consequent variation in the power of the remaining channels can
cause system performance degradation as well as system component
damage due to high-power overshoots. Two main methods have been
proposed for solving this problem: the electronic control of OA gain
by using a suitable electrical feedback circuit, and optical-gainclamping
(OGC). The first method requires an extra system management
layer and it may not completely eliminate the surviving channel
power overshoot. In contrast, OGC is a passive, all-optical technique
[1, 2] where the OA becomes a laser with clamped, i.e. fixed, gain.
However, variation in signal input power causes oscillations in output
power with the possibility of generating large peak overshoot after a
sequence of inline OAs [3] due to the finite response time of the
OGC-OA. We have recently proposed a new theoretical approach to
model the dynamical behaviour of both erbium-doped and erbiumytterbium-
doped optical amplifiers (EDFA and EYDFA) [4, 5]. We
have also demonstrated theoretically and experimentally that erbiumdoped
waveguide optical amplifiers (EDWAs) offer fast transient
recovery time owing to short photon cavity lifetime [4, 6]. In addition
we have shown that a short-cavity OGC-OA strongly reduces the extra
pump power required for OGC and thus the overall component
fabrication and operation cost. However, fully integrated-component
design based on waveguide amplifiers may need further technological
development.
Introduction: The introduction of WDM systems into metropolitanareas poses a main challenge to address system sensitivity to channelnumber reconfiguration. In fact, channel add=drop may introduce astrong variation in the operation point of the optical amplifiers (OAs)and consequent variation in the power of the remaining channels cancause system performance degradation as well as system componentdamage due to high-power overshoots. Two main methods have beenproposed for solving this problem: the electronic control of OA gainby using a suitable electrical feedback circuit, and optical-gainclamping(OGC). The first method requires an extra system managementlayer and it may not completely eliminate the surviving channelpower overshoot. In contrast, OGC is a passive, all-optical technique[1, 2] where the OA becomes a laser with clamped, i.e. fixed, gain.However, variation in signal input power causes oscillations in outputpower with the possibility of generating large peak overshoot after asequence of inline OAs [3] due to the finite response time of theOGC-OA. We have recently proposed a new theoretical approach tomodel the dynamical behaviour of both erbium-doped and erbiumytterbium-doped optical amplifiers (EDFA and EYDFA) [4, 5]. Wehave also demonstrated theoretically and experimentally that erbiumdopedwaveguide optical amplifiers (EDWAs) offer fast transientrecovery time owing to short photon cavity lifetime [4, 6]. In additionwe have shown that a short-cavity OGC-OA strongly reduces the extrapump power required for OGC and thus the overall componentfabrication and operation cost. However, fully integrated-componentdesign based on waveguide amplifiers may need further technologicaldevelopment.
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