Multi-format transmitters for coherent optical M-PSK and M-QAM transmission
Coherent optical transmission returns into the focus of research. One significant advantage is the preservation of all the information of the optical field during detection, leading to enhanced possibilities for optical multi-level modulation. This paper investigates the generation of optical multi-level modulation signals. Several possible structures of optical M-PSK and M-QAM transmitters are shown and theoretically analyzed. Differences in the optical transmitter configuration and the electrical driving lead to different properties of the optical multi-level modulation signals. This is shown by deriving general expressions applicable to every M-PSK and M-QAM modulation format and exemplarily clarified for square-16-QAM modulation.