WDM optical communication: fundamental capacity limits with ASE noise and optical nonlinear effects

Wavelength division multiplexing (WDM) has become a fundamental technology for meeting the rapidly increasing demand for high-capacity optical communication networks. While significant advancements have been achieved through improved modulation formats and optical amplification, the ultimate performance of WDM systems is fundamentally constrained by physical-layer impairments and information-theoretic limits. This paper presents a comprehensive information-theoretic analysis of the capacity limits of WDM optical communication systems. Starting from Shannon’s channel capacity theorem, analytical expressions for channel capacity are derived by incorporating key optical impairments, including amplified spontaneous emission (ASE) noise, optical signal-to-noise ratio (OSNR), chromatic dispersion, and fiber nonlinearities. The relationship between modulation formats, OSNR, and achievable spectral efficiency is investigated. Numerical evaluations demonstrate how system parameters such as launch power, channel spacing, and amplifier noise figure influence the achievable capacity per channel and total WDM system capacity. The presented analysis provides valuable theoretical insight into the fundamental performance limits of WDM systems and serves as a guideline for the optimal design of high-capacity optical networks.