Abstract
This paper addresses transmission aspects on very high aggregate
wavelength-division multiplexing based passive optical networks (WDM-PON).
The ultradense WDM-PON system evaluated in this paper transports
high-order modulation formats such as M-ary phase-shift keying
(PSK) and M-ary quadrature amplitude modulation (QAM) in which coherent
detection is performed at the optical network unit (ONU), after transmission
over 25 km, 60 km, and 100 km of standard single-mode fiber (SSMF). The
first part of this work covers the impact on the system's performance of the
most relevant fiber nonlinearities such as self-phase modulation (SPM),
cross-phase modulation (XPM) and four-wave mixing (FWM), and their interplay
between transmission distance and modulation format. Using a Volterra series
method allows estimating the error vector magnitude (EVM) of the received
constellation related to different fiber nonlinearities. In a 32 × 625 Mbaud system spaced by 3
GHz (0.025nm), the FWM to XPM ratio (F/X) varied from 25
up to 30 dB for phase-modulated signals (1.25 Gb/s-QPSK and 1.875
Gb/s-8PSK). On the other hand, this ratio ranged from 2.6 to 7.4 dB for
amplitude-modulated signals (2.5 Gb/s-16QAM, 3.75 Gb/s-64QAM and 5
Gb/s-256QAM). After applying a frequency-allocation scheme at both
transmitter and local oscillator lasers, some of the FWM crosstalk is
mitigated by 2.4 to 3.5 dB. This EVM reduction confirms that increasing the
transmission distance and the order of the constellation, the system's
performance becomes limited by both interchannel FWM and XPM.
© 2011 IEEE
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