WDM technology relies on the fact that optical fibers can carry many wavelengths of light simultaneously without interaction between each wavelength. Thus, a single fiber can carry many separate wavelength signals or channels simultaneously. This capacity to wavelength multiplex signals in one fiber has led to the tremendous increase in bandwidth available to power the Internet around the globe. Certain key products are required to make WDM possible.
Optical amplifiers operate based on the stimulated emission process.
Each signal photon stimulates the emission of 10 to 100 or more identical photons from erbium atoms with electrons excited to a high-energy state through the absorption of photons at wavelengths of either 980 nm or 1480 nm. Due to stimulated emission, the amplified output signal matches both the wavelength and pulse shape of the input signal. A third key product is the signal generating transmission laser. Each signal laser emits light at a single precisely defined wavelength. Each wavelength channel requires a separate signal-generating transmission laser.