The article pointed that market demand for 40Gbit/s is clear now

relevant technologies are mature

cost is approaching the threshold of taking off and mass deployment will start soon. Then

the article analyzed and investigated a couple of key technical issues such as chromatic dispersion

PMD

non-linear impairments

requirement of optical signal to noise ratio

selection of modulation formats

super FEC

selection of color and colorless interfaces

etc.. Finally

the article discussed status and prospects of 100Gbit/s systems and development strategy for 40/100Gbit/s systems in brief.