Abstract
In this paper, we present an in depth analysis and discussions
on the behavior and performance of using either thin or thick second
harmonic generation (SHG) crystals prior to photodetector in ultrahigh-speed
optically amplified digital lightwave communication systems. Our study
begins by considering a conventional low-speed optically amplified lightwave
receiver and study its performance in ultrahigh-speed regime and show its
substantially degraded behavior, indicating the need to use advance optical
nonlinear elements such as SHG prior to photodetection. In studying SHG
effects, we begin by discussing the mathematical models of thin and thick
SHG crystals in the context of statistical digital lightwave communication
systems. In the case of thin SHG crystals and in the regime of high-speed
digital systems, where Gaussian assumption is not necessarily valid, we use
advanced numerical simulation based on Monte Carlo simulation to obtain its
corresponding performance. However, for thick SHG crystals by invoking an
advanced theorem due to Papoulis on gaussianity approximation and a lemma
due to Turin, we obtain the moment generating function of the sampled output
with which, we obtain its corresponding performance using saddle point
approximation method. Finally in our performance analysis, we consider
electronically induced thermal noise and sketch the performance for various
system parameters. The results in this paper indicate that the use of SHG
crystals can enhance the system performance, when compared with the
conventional receiver, by a substantial amount, i.e., five orders of
magnitude. Furthermore, we highlight the existence of an optimum length for
thick SHG crystals in the presence of thermal and optical amplifier
noise.
© 2009 IEEE
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