DWDM

DWDM stands for dense wavelength division multiplexing, a fiber-optic transmission technique that packs multiple distinct light wavelengths, or channels, onto a single optical fiber to carry separate data streams concurrently. By using a tightly spaced wavelength grid, DWDM increases the total capacity of a fiber link beyond what a single wavelength could carry. Channels are typically spaced on ITU-T grids around 100 GHz, with 50 GHz spacing also used in many modern systems, primarily within the C-band (approximately 1525 to 1565 nm) and increasingly in the L-band.

In operation, laser transmitters generate light at different wavelengths, which are combined by a DWDM multiplexer and sent over one fiber. At the distant end, a demultiplexer separates the wavelengths for individual reception. Inline devices such as optical add-drop multiplexers (OADMs) and wavelength-selective ROADMs enable dynamic routing and partial channel extraction along the trail. Amplification using erbium-doped fiber amplifiers (EDFAs) counteracts loss, and higher performance systems employ coherent detection with digital signal processing, enabling advanced modulation formats (for example PM-QPSK, PM-16QAM) and high spectral efficiency for long-haul links.

DWDM supports high aggregate capacity without additional fibers: systems commonly carry dozens to hundreds of channels per fiber, each channel at tens to hundreds of gigabits per second, yielding terabit-per-second or higher aggregate data rates. The technology is central to optical backbone networks, data-center interconnects, and metro networks, offering scalability, flexibility, and automation through ROADM-based architectures. Key considerations include dispersion and nonlinear effects, network planning on ITU grids, and compatibility with existing fiber types and amplification schemes.