High-SNR OAM mode division multiplexing based on delta-sigma modulation using a power domain layer

Orbital angular momentum (OAM) mode-division multiplexing (MDM) systems exist with mode cross talk, which requires high signal-to-noise ratio (SNR) to improve transmission performance. In this Letter, a novel, to the best of our knowledge, scheme, based on power domain layered delta-sigma modulation (PDL-DSM) was proposed, which composes a high-order signal into two low-order signals and quantizes them using two parallel DSMs. The transmission efficiency of the quantized signals is optimized by using power domain multiplexing, and the quantization noise of the high-power signals is eliminated to improve the overall SNR of the system. The experimental results show that the PDL-DSM scheme achieves the transmission of 65,536 QAM signals, and the bit error rate (BER) is below the hard-decision forward error correction (HD-FEC) threshold for -3 dBm and 5 dBm in two modes. Under the same experimental conditions, the PDL-DSM outperforms the multi-stage noise-shaping (MASH) scheme and the 2-bit DSM scheme in both OAM modes. The PDL-DSM scheme outperforms the MASH DSM scheme when transmitting 1,048,576 QAM and increases the receiver sensitivity by 3 dB at the HD-FEC threshold for OAM mode <i>l</i> = 3. Compared with the traditional 2-bit DSM scheme, the PDL-DSM scheme has a SNR gain of the recovered waveform with 15 dB.