Fig. 1. Schematic of the proposed Stokes-MTL-DNN.

Fig. 2. S₁ and Δφ distribution features of PDM-QPSK/8-QAM/16-QAM/64-QAM with low and high OSNRs.

Fig. 3. Illustration of the experimental setup of the coherent optical PDM BTB transmission system.

Fig. 4. Accuracy of MFI for BTB PDM QPSK/8-QAM/16-QAM/64-QAM with different OSNR values.

Fig. 5. MAE of OSNR monitoring for BTB PDM QPSK/8-QAM/16-QAM/64-QAM under different OSNR values.

Fig. 6. MAE of OSNR monitoring for BTB PDM-QPSK/8-QAM/16-QAM/64-QAM under residual CD.

Fig. 7. Schematic diagram of the PDM QPSK/8-QAM/16-QAM/64-QAM long-haul transmission simulation link.

Fig. 8. MAE of OSNR monitoring versus different launching powers.