Interesting read.

http://www.lightwaveonline.com/articles/2016/08/iii-v-and-silicon-friends-or-foes-for-400-gigabit-ethernet.html

"What is further on the horizon of photonic integration? The Holy Grail would be a single housing in which all optical and the essential electrical drivers are co-packaged in a non-hermetic form. Among those components could be new building blocks for optical signal preprocessing to reduce the workload and power consumption of the DSP ASIC, e.g., optical dispersion compensation, input polarization rotators, and the like. The boundary between direct-detect and coherent technologies in the future might shift further to enable coherent-only transmission outside of the data center. The industry certainly might see 400GbE coherent variants of the aforementioned form factors (CFP8, QSFP-DD), although questions of power consumption and cost will remain looming over coherent technology before it can really claim the sub-80-km market fully for itself."