The components of a traditional DWDM system consists of the transponder, multiplexer/de-multiplexer, optical add/drop multiplexers, and optical amplifiers.

Below is a high level overview of the process in which data is transmitted using DWDM and what each component’s function is within the system:
1. The data stream comes in via the router and is input into the transponder.
2. The transponder maps the signal to a DWDM wavelength and sends it to the multiplexer (Mux) to consolidate the optical signal.
3. As the signal leaves the multiplexer, optical amplifiers boost the signal to allow the signal to travel over longer distances.
4. Along the way, optical add/drop multiplexers (OADM) can add and remove bitstreams of a specific wavelength. Also, additional amplifiers can be used to further boost the signal’s distance.
5. The signal the arrives and gets de-multiplexed (DeMux) into individual DWDM wavelengths, which are then passed through the transponder to be converted into the corresponding signals to be routed to its final destination.

Optical transmitters and receivers

Optical transmitters and receivers are fundamental components of DWDM systems. Multiple transmitters in each system provide source signals before they are multiplexed, with several individual lasers deployed to handle different channels in the signal.

Each optical transmitter is fed with electronic data bits – ones and zeros – which trigger the modulation of precise optical pulses. To represent ‘one’, the transmitter’s laser generates a pulse of light. To represent ‘zero’, the laser remains inactive.

The pulses of light then travel the length of the optical fibre, where they are demultiplexed before terminating at optical receivers. These optical receivers detect the light pulses and convert them back into electronic data bits.

DWDM mux and demux filters

The mux filter receives different signals from the optical transmitters via multiple fibres. It then combines and transmits them as a composite signal over a single optical fibre.

At the demux filter on the receiving terminal, all the separate wavelengths of the composite signal are separated and sent down different fibres to the optical receivers.

Mux and demux devices are usually passive, requiring no power supply or maintenance to function correctly.

Optical add/drop multiplexers

Optical add/drop multiplexers (OADMs) are installed at intermediate points along a transmission line. They enable new signals to enter the network and existing signals to leave, separating or rerouting different wavelength channels.

Most signals simply pass through the OADM unchanged, but some are dropped by splitting them from the line. At the same time, signals originating at that point can be added and transmitted to another destination.

Reconfigurable optical add-drop multiplexers (ROADMs) are now widely used, allowing the routing and rerouting of any wavelength in any direction.

Optical amplifiers

Optical amplifiers enhance optical signals by directly stimulating photons, increasing amplitude and strengthening the signal.

They’re built into the fibre and can amplify signals over a wide range of wavelengths. A vital part of DWDM systems, they greatly extend the transmission distances of DWDM equipment.

RAMAN amplifiers can be used to allow transmission over longer distances.

Optical transponders

An optical transponder, also known as an O-E-O (optical-electrical-optical) wavelength converter, is a crucial signal transmission component. It gathers incoming optical signals from the client service and converts them to outgoing optical wavelengths compatible with DWDM components.

First, it converts the optical signal into an electrical signal. It then performs either 2R (reamplify and reshape) functions or 3R (reamplify, reshape and retime) functions. Finally, it converts the signal back into an optical signal, hence the name O-E-O.