How is wavelength division multiplexing used?

What will be an ideal response?

Wavelength division multiplexing (WDM) is used with fiber-optics in a manner similar to how frequency-division multiplexing is used with copper. Wavelength division multiplexing uses lasers to transmit different frequencies of light through the same fiber-optic cable. At the sending end, narrow bands of light are combined into a wider band. The wider band is the high-speed circuit. At the receiving end, the signals are separated. A more complex form of wavelength division multiplexing is dense wavelength division multiplexing. Dense wavelength division multiplexing (DWDM) combines wavelength division multiplexing with time-division multiplexing. Using DWDM, one fiber-optic cable can send up to 400 Gbps (billions of bits per second).