Realization of DSM-Based 65536-QAM Transmission in Hollow-Core Fibers Using Noise-Erase Scheme

Delta-Sigma modulation (DSM) has been widely adopted in high-performance signal processing systems due to its significant advantages in realizing ultra-high-order modulation schemes. However, while conventional DSM effectively shapes and push the quantization noise out of band, the residual in-band quantization noise may still adversely affect transmission performance, thereby limiting the overall system efficiency. This study proposes an innovative noise-erase based DSM enhancement method: initially constraining in-band noise through low-pass filtering and noise shaping techniques, followed by power-domain superposition to directly combine the processed in-band quantization noise with DSM signals for transmission. This breakthrough solution significantly improves in-band signal-to-noise performance without substantially increasing the oversampling ratio. Experimental verification is conducted on an Intensity Modulation and Direct Detection (IM/DD) system over 1.5 km of hollow-core fiber (HCF). The proposed scheme demonstrates the capability to achieve extremely high-order 65,536-quadrature amplitude modulation (QAM) transmission without occupying additional channel resources. The receiver sensitivity is improved by 0.5 dB compared to traditional DSM, and the signal-to-noise ratio (SNR) gain can reach up to 20 dB.