Four-dimensional modulation formats with coherent detection for spectrally efficient fiber-optic communication systems

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Four-dimensional (4D) coded modulation is a promising technique to approach the potential capacity of fiber optic channels and thus offers a way to satisfy the ever growing need for higher transmitted bit rates in the optical backbone networks. Within the project, 4D coded modulation schemes are to be developed and demonstrated experimentally. In particular, two schemes will be investigated:(1) 4D m-ary set partitioning quadrature amplitude modulation (mSP-QAM) in conjunction with 4D turbo codes,(2) 4D Trellis coded modulation.Four-dimensional mSP-QAM constellations are derived from conventional polarization-division multiplexed (PDM) QAM constellations by applying Ungerböcks set partitioning scheme in four dimensions and thus increasing the noise tolerance. For example, 128SP-QAM can be derived from PDM-16QAM by applying 4D set partitioning once.Similarly, 4D Trellis coded modulation applies Trellis coded modulation to four-dimensional constellations instead of using two-dimensional ones. The goal of the project is to show that these techniques can be applied to significantly increase the spectral efficiency times reach product compared to state-of-the-art systems. To that end, the benefits brought by 4D coded modulation will not only be quantified in numerical simulations but also be demonstrated in laboratory experiments.