7.4.4 Summary Of WDM

Wavelength-division multiplexing dramatically increases the transmission capacity of optical fiber by allowing multiple independent optical carriers to propagate simultaneously at different wavelengths. By operating in the low-loss 1550 nm window and employing dense channel spacing, modern WDM systems form the backbone of global high-capacity telecommunications networks, enabling multi-terabit-per-second transmission over single optical fibers.

While WDM separates channels in the optical frequency domain, orthogonal frequency-division multiplexing (OFDM) operates within a single transmission band and divides it into many closely spaced, mathematically orthogonal subcarriers. The subcarriers are mathematically orthogonal over the symbol period, meaning that their cross-correlation is zero, allowing their spectra to overlap without mutual interference. Unlike WDM, which is primarily an optical transport technique, OFDM is a digital modulation strategy widely used in wireless and broadband systems.