Wavelength Division Multiplexing (WDM) allows multiple optical signals to transmit over a single fiber by using different wavelengths of light. It increases fiber network capacity without requiring additional fibers, making it essential for modern optical communication. This guide delves into the principles, types, applications, and future trends of WDM. It provides an expert-curated supplier directory, buyer-focused technical background information, and structured selection criteria to support professional procurement decisions.