Abstract
We present yet another quasi-analytic model for an optically amplified
receiver, comprising an optical preamplifier, an optical prefilter, a photodetector,
and an electrical postfilter. Due to the square-law nonlinearity and its interaction
with the linear pre- and postfilters, the understanding of this seemingly
simple structure has been elusive, gradually evolving over a succession of
studies, culminating in the models by Lee and Shim and Forestieri. Here we
adopt a new approach to this old problem, applying Volterra nonlinear theory
to obtain fresh insight deriving a simplified model streamlining the pseudoanalytic
simulations. Volterra series is a powerful mathematical tool for simulating
nonlinear systems, applied here to quadratic optical detection in an unconventional
way, by deriving a mixed frequency-time representation, leading to a simple
and compact quadratic form in the combined signal-plus-noise signal spectra,
albeit not computationally efficient. Next, Forestieri's results, which used
distinct bases for the signal and noise, are rederived using the insightful
Volterra formalism. Finally, we reformulate the model using an expansion of
both signal and noise in a common harmonic basis over a sliding window of
duration equal to the ISI system memory. This final version of the optically
amplified receiver model is most computationally efficient, provides the most
compact description, and lends itself to intuitive interpretation. Applications
of the new method include accurate determination of the bit error ratio of
amplitude-shift keying, frequency-shift keying, and differential phase-shift
keying transmission systems in the linear optical link propagation regime,
including the effects of dispersion and fully accounting for intersymbol interference.
The theory developed here is naturally extensible to advanced optical equalization
techniques, involving Volterra nonlinear optoelectronic equalizers.
© 2008 IEEE
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