Multilevel ASK Amplitude Level Optimization in the Presence of Chromatic Dispersion and PMD

Abstract:
Offering reduced bandwidth occupancy and increased symbol duration, multilevel modulation formats promise a higher robustness towards chromatic dispersion (CD) and polarization mode dispersion (PMD) than binary formats. Especially for multi-level amplitude shift keying formats, which are promising candidates for cost efficient future metro networks at 100 Gb/s, this robustness substantially depends on the choice of the amplitude levels for the format. For example, optimum levels for maximum back-to-back receiver sensitivity do not necessarily lead to the highest CD or PMD tolerance. Within this paper, we show the influence of CD and PMD on the transmitted multi-level signal. We introduce four different methods of choosing the amplitude levels and determine the resulting impairment tolerance of the modulation formats. The results show that the requirements of every format are different depending on the impairment. The considered modulation formats are 2-, 4- and 8-ASK in unipolar and bipolar forms. Bipolar ASK formats are generated as a mixture of ASK and differential binary phase shift keying (DBPSK).