What are the design considerations for WDM optical transmission systems?

WDM (Wavelength Division Multiplexing) transmits multiple wavelengths on single fiber. Design considerations: Channel spacing (100GHz, 50GHz, or flex-grid DWDM), wavelength plan and guard bands, amplifier design (EDFA gain flatness across band, noise figure), fiber nonlinearity management (self-phase modulation, cross-phase modulation, four-wave mixing), dispersion map design, OSNR requirements per channel, and amplifier spacing. Advanced systems: Coherent detection enables higher spectral efficiency, flex-grid allows varied channel widths, and Raman amplification extends reach. Capacity exceeds 10 Tbps per fiber in modern systems.