Future Internet and Ethernet technologies will be affected by both limited bandwidth of information infrastructure and its high energy consumption. In order to solve both problems simultaneously, in this invited paper, we describe several hybrid coded-modulation (CM) schemes enabling multiterabit optical transport including spatial-domain-based CM, mode-multiplexed 4-D CM, and mode-multiplexed generalized orthogonal frequency division multiplexing. A common property of these CM schemes is the employment of optimized signal constellations, various degrees of freedom, and rate-adaptive coding. These modulation schemes are called hybrid as all available degrees of freedom are used for transmission over optical fibers including amplitude, phase, polarization, and orbital angular momentum. Since the channel capacity is a linear function in number of dimensions, by increasing the number of basis functions, we can dramatically improve the overall system capacity. The energy-consumption problem is tackled by properly designing multidimensional signal constellations such that transinformation is maximized, while taking the energy constraint into account.
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