An optical transmitter device comprising: a digital signal processor, DSP, comprising digital hardware, the DSP operative to generate shaped bits from a first set of information bits using probabilistic constellation shaping, PCS; to apply a systematic forward error correction, FEC, scheme to encode the shaped bits and a second set of information bits, where the first set of information bits and the second set of information bits are disjoint sets; and for multiple pairs of groups, each pair consisting of a first group and a second group, each first group consisting of a first unshaped bit and a first shaped bit of the shaped bits and each second group consisting of a second unshaped bit and a second shaped bit of the shaped bits, to map the first unshaped bit and the first shaped bit to a first quadrature phase shift keying, QPSK, symbol according to a labeling scheme; to map the second unshaped bit and the second shaped bit to a second QPSK symbol according to the labeling scheme; and to map the first QPSK symbol and the second QPSK symbol to four physical dimensions, wherein each unshaped bit is either one of the second set of information bits or one of multiple parity bits resulting from the FEC encoding; and wherein either the least significant bit in all groups is always one of the shaped bits or the most significant bit in all groups is always one of the shaped bits. a digital signal processor, DSP, comprising digital hardware, the DSP operative to generate shaped bits from a first set of information bits using probabilistic constellation shaping, PCS; to apply a systematic forward error correction, FEC, scheme to encode the shaped bits and a second set of information bits, where the first set of information bits and the second set of information bits are disjoint sets; and for multiple pairs of groups, each pair consisting of a first group and a second group, each first group consisting of a first unshaped bit and a first shaped bit of the shaped bits and each second group consisting of a second unshaped bit and a second shaped bit of the shaped bits, to map the first unshaped bit and the first shaped bit to a first quadrature phase shift keying, QPSK, symbol according to a labeling scheme; to map the second unshaped bit and the second shaped bit to a second QPSK symbol according to the labeling scheme; and to map the first QPSK symbol and the second QPSK symbol to four physical dimensions, to generate shaped bits from a first set of information bits using probabilistic constellation shaping, PCS; to apply a systematic forward error correction, FEC, scheme to encode the shaped bits and a second set of information bits, where the first set of information bits and the second set of information bits are disjoint sets; and for multiple pairs of groups, each pair consisting of a first group and a second group, each first group consisting of a first unshaped bit and a first shaped bit of the shaped bits and each second group consisting of a second unshaped bit and a second shaped bit of the shaped bits, to map the first unshaped bit and the first shaped bit to a first quadrature phase shift keying, QPSK, symbol according to a labeling scheme; to map the second unshaped bit and the second shaped bit to a second QPSK symbol according to the labeling scheme; and to map the first QPSK symbol and the second QPSK symbol to four physical dimensions, to map the first unshaped bit and the first shaped bit to a first quadrature phase shift keying, QPSK, symbol according to a labeling scheme; to map the second unshaped bit and the second shaped bit to a second QPSK symbol according to the labeling scheme; and to map the first QPSK symbol and the second QPSK symbol to four physical dimensions, wherein each unshaped bit is either one of the second set of information bits or one of multiple parity bits resulting from the FEC encoding; and wherein either the least significant bit in all groups is always one of the shaped bits or the most significant bit in all groups is always one of the shaped bits.