The future optical transport networks will be affected by limited bandwidth of information infrastructure, high power consumption, and heterogeneity of network segments. As a solution to all these problems, the multidimensional signaling has been proposed recently. In this invited paper, we follow a different strategy. Instead of conventional binary and 2mary signaling (m≥1) we propose to use the nonbinary pm-ary signaling, where p is a prime larger than 2. With pm-ary signaling we can improve the spectral of conventional 2m-ary schemes by log2p times for the same bandwidth occupancy. At the same time the energy efficiency of pm-ary signaling scheme is much better than that of 2m-ary signaling scheme based on binary representation of data. We further study the energy-efficient coded modulation for pm-ary signaling. The energy-efficient signal constellation design for pm-ary signaling is discussed as well. We will demonstrate that with the proposed pm-ary signaling in combination with energy-efficient signal constellation design, spectral-multiplexing, and polarization-division multiplexing, we can achieve beyond 1 Pb/s serial optical transport without a need for introduction of spatial-division multiplexing.
The joint optimization of coding and modulation formats would provide significant receiver sensitivity improvement due to the increased Hamming distance of codes. By applying Arimoto-Blahut algorithm to maximize mutual information, optimized coded-modulation has been found out together with optimized bit-mapping rule. Simulated channel capacity shows that optimized coded modulation could outperform its counterparts, such as regular qaudrature-amplitude modulation, by around 0.3dB up to about 0.9 coding rate. The improvement is found to be larger in higher modulation formats. Optimal coded-8QAM modulation has been further verified in experiment, where 40Tb/s over 6787km is demonstrated by transmitting 200G per wavelength thanks to the better receiver sensitivity of optimal coded modulation.
We propose the general idea of constructing an ultra-compact optical pickup based on photonic crystals. A few optical components necessary for various functions of an optical head are designed and analyzed.