Abstract
In this paper, closed-form analytical bounds on PMD-induced symbol error
rate and outage probability in high-speed long-haul optical orthogonal frequency
division multiplexed (OFDM) systems are derived, evaluated, and verified experimentally
in order to assess the PMD tolerance of this modulation format. To obtain
the analytical results, the PMD channel is modeled as a linear time-invariant
system, whose end-to-end transfer function is used to upper-bound symbol error
and outage probabilities in IM/DD optical OFDM transmission. The symbol error
rate bounds predicted by the general analytical model are verified experimentally
on a 10-Gb/s OFDM system with instantaneous DGD ranging between $\Delta\tau = 0$ and 120 ps.
The outage probability bounds indicate that, if no RF guard bands are required,
OFDM enables high-speed transmission with at least twice the PMD tolerance
provided by an equivalent uncompensated OOK-based system at system outage
probabilities $P_{{\rm out,\ sys}}<10^{-5}$. If RF guard bands are required to mitigate effects of other distortions,
it is shown that a penalty in the system PMD tolerance proportional to the
intermediate RF subcarrier frequency, $f_{{\rm
RF}}$, is exerted. Consequently, a tolerance tradeoff exists
in IM/DD OFDM systems, wherein $f_{\rm
RF}$ as well as baseband constellation size may be viewed
as design parameters that can be optimized depending on specific system requirements.
© 2008 IEEE
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