Multidimensional PAM With Pseudo-Gray Coding for Flexible Data Center Interconnects

Conventional modulation formats for single carrier transmission do not provide the flexibility to gradually scale the data rate and spectral efficiency. By using multidimensional pulse-amplitude modulation, fractional numbers of bits per symbol can be achieved, which extends the flexibility and reach of intensity modulation and direct detection systems but keeps the signal processing simple. By using pseudo-Gray coding, we are able to achieve optimum mappings for various non-integer bits-to-symbol assignments. We show a transmission experiment with data rates ranging from 56 to 168 Gb/s in fine granularity over different link lengths at a symbol rate of 56 GBd.