Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-character. Today, DWDM is a crucial component of optical networks because it maximizes the use of installed fiber cable and allows new services to be quickly and easily provisioned. This tutorial covers the fundamentals of DWDM (Dense Wavelength Division Multiplexing), including the DWDM transmitter and receiver. We'll also delve into optical fiber basics, optical amplifiers (EDFA), and other essential system components. DWDM is essentially an optical multiplexing technique.