Novel Transponder Interfaces: Novel Modulation Formats

For a long period of time, the modulation format in optical communications technology was based on intensity modulation with an on/off - keying signalling, using NRZ and sometimes RZ pulse-shapes. However with today's requirements for very high capacity networks with constraints on cost efficiency, more advanced solutions are required. Advanced modulation formats are considered as one of the key issue in the networks of the future. With novel modulation formats we have the general options to modulate the amplitude or the phase or both of the optical carrier signal of a coherent laser. An additional degree of flexibility can be achieved by using polarization (division) multiplexing (PDM). The table gives an overview of the currently discussed options.