C-Band 53.76 Tbit/s Transmission Based on Bit Allocation Optimization with Raman Amplification

We experimentally demonstrate an 80-channel wavelength division multiplexing (WDM) transmission system over a 400 km fiber link. Raman amplification results in a non-flat WDM signal spectrum. Therefore, bit allocation optimization is used to enable different channels to carry different order quadrature amplitude modulation signals according to their optical signal-noise-ratios. A neural network equalizer based on a convolutional neural network (CNN), long short-term memory (LSTM) network, and fully connected (FC) layer structure is adopted in Rx digital signal processing, in which CNN is used for characteristic extraction, LSTM is used for equalization and demodulation, and FC layers are used for output. After transmission, the bit error rate of all channels is below the 25% soft-decision forward error correction threshold, and the line rate reaches 53.76 Tbit/s.