Performance comparison of traditional and Nyquist shaped signals incorporating modulation format based optical channel aggregation for enhanced spectral efficient transmission

Abstract As the demand for channelled data streams continues to exceed the throughput limits of current wavelength-division multiplexing (WDM) systems, the evolution of optical networks requires the adoption of spectrally efficient modulation techniques. Achieving high spectral efficiency at extremely high data rates, however, often relies on complex and bandwidth-intensive transceiver hardware. Practical applications of wavelength channel consolidation and modulation format conversion further demand adaptability in data rates, bandwidth, and variability. The requirements of such systems are inherently dependent on the characteristics of the employed modulators and radio-frequency (RF) sources. To address these challenges, this work proposes an all-optical aggregation scheme that consolidates low-spectral-efficiency optical wavelength channels, generated from an optical frequency comb-based source, into spectrally efficient, higher-capacity streams. The approach exploits coherent spectrum stacking and optical vector addition, thereby eliminating the need for optical phase irregularity compensation and enabling linear signal processing through an electro-optic modulator. Optical phase control for precise vector addition in the in-phase (I) and quadrature (Q) plane is achieved by simply tuning the phase of the RF driving signal, ensuring robust and flexible implementation. The proposed framework is evaluated using both conventional and sinc-shaped Nyquist sampling, demonstrating that the in-line all-optical aggregation technique not only enhances transmission capacity but also reduces system complexity. This approach offers a practical pathway toward flexible and integrated optical transmitters capable of generating advanced modulation formats using relatively simple electronic hardware, representing a key enabler for next-generation high-capacity communication systems.