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