With the continuously growing demand for optical network bandwidths

multi-dimensional and multi-level modulation formats

such as 8PSK

8QAM

16QAM

have become a current focal point of research.In this paper

we make a comprehensive comparative analysis of the principles and topologies for the realization of these formats and obtain 8PSK

8QAM and 16QAM modulated optical signals by using commercially available modulation devices configured in a serial or hybrid structure.We can improve the system integration level and signal transmission performances by using configuration in a parallel structure

but it often needs multiple parallel structures

which raises harsh requirements on the cost and processes for system integration.