Proceedings Article | 10 September 2007
KEYWORDS: Modulation, Orthogonal frequency division multiplexing, Transmittance, Receivers, Phase shift keying, Computer programming, Dispersion, Multiplexing, Quadrature amplitude modulation, Nonlinear optics
The future Internet traffic growth will require deployment of optical transmission systems with bit rates higher than rate
of currently available 40-Gb/s systems, such as 100-Gb/s and above. However, at data rates beyond 100-Gb/s the signal
quality is significantly degraded mainly due to impact of polarization mode dispersion (PMD), and intra-channel
nonlinear effects. All electrically time-division multiplexed (ETDM) multiplexers and de-multiplexers operating at
~100-Gb/s are becoming commercially available. However, the modulators operating ~100-Gb/s are not widely
available so that alternative approaches to enable 100-Gb/s transmission and beyond using commercially available
components operating at 40-Gb/s are of high practical importance. In this invited paper, several joint coded-modulation
and multiplexing schemes enabling beyond 100-Gb/s transmission using commercially available components operating
at 40-Gb/s are presented. Using this approach, modulation, coding and multiplexing are performed in a unified fashion
so that, effectively, the transmission, signal processing, detection and decoding are done at much lower symbol rates,
where dealing with the nonlinear effects and PMD is more manageable, while the aggregate data rate is maintained
above 100-Gb/s. The main elements of our approach include: (i) bit-interleaved LDPC-coded modulation, (ii) multilevel
coding (MLC) with LPDC component codes, and (iii) LDPC-coded orthogonal frequency division multiplexing
(OFDM). The modulation formats of interest in this paper are M-ary quadrature-amplitude modulation (QAM) and Mary
phase-shift keying (PSK), where M=2,...,16, both combined with either Gray or natural mapping rule. It will be
shown that coherent detection schemes significantly outperform direct detection ones and provide an additional margin
that can be used either for longer transmission distances or for application in an all-optical networks.
