DOI: 10.22184/1993-7296.FRos.2026.20.1.30.42
DP-nQAM modulation formats used in modern coherent fiber-optic transmission systems with digital signal processing are considered. In such formats, data is transmitted independently in two polarizations and using nQAM quadrature modulation in each of them, where n = 2k. The symbol efficiency of such modulation formats is equal to SmE = 2k. The disadvantage of traditional formats is the inability to implement intermediate values of symbol efficiency between two consecutive values. As a result, it is possible that the quality of the signal in the communication line, determined by the optical (electrical) signal-to-noise ratio, significantly exceeds the requirements for the format with SmE = 2k, but not enough to work with the SmE = 2 (k + 1) format. This article (Parts 1 and 2) discusses new modulation formats in which, for each polarization, 2k symbol values are used, as in traditional DP-nQAM formats, but the probabilities of different symbols appearing are different. When using such modulation formats, smooth adjustment of the SmE can be achieved, which allows for maximum bandwidth of the communication line at an arbitrary communication range.