Progress in optical modulation formats for high-bit rate WDM transmissions

With the progress of optical communication systems, and especially the constraints brought by wavelength division multiplexing (WDM) transmissions and increased bit rates, new ways to convert the binary data signal on the optical carrier have been proposed. It appears clearly now that several of the methods proposed by research laboratories will be applied into commercial products soon due to the large improvements generated. This paper intends to summarize some of the most interesting proposed modulation formats for high bit rate (especially 40 Gb/s) WDM transmissions