Wavelength Division Multiplexing (WDM)

What is WDM?

Wavelength Division Multiplexing (WDM) is a fiber optic transmission technology. It allows multiple wavelengths of light signals to transmit data simultaneously over the same medium. This means that different wavelengths of signals can be coupled onto a single fiber, enabling parallel transmission of multiple data streams on one fiber.

TDuring transmission, the fiber acts like a multi-lane highway, with different wavelengths of signals representing different types of vehicles. Traditional Time Division Multiplexing (TDM) uses just one lane, increasing the speed to allow more vehicles to pass through, essentially raising the bit rate to boost transmission capacity.

In contrast, WDM uses multiple lanes, allowing various vehicles to travel down the highway and then separate into their respective lanes as they near their destination.

Today’s world has an enormous demand for the internet, leading to a need for more fiber optic cables than are currently available. Additionally, the primary issue with fiber optics is signal wastage. These challenges drive the adoption of WDM technology. It increases fiber transmission capacity and improves efficiency.

Clearly, WDM holds tremendous potential in fiber optic communications. It can help operators stay ahead of the growing bandwidth demands.

How Wavelength Division Multiplexing Works?

WDM technology in fiber optic communication is implemented using multiplexers (MUX) and demultiplexers (DEMUX). These devices are deployed in the network to implement WDM technology.

During transmission, multiple light signals of different wavelengths are combined at the sending end by MUX. These signals are transmitted together through a single optical fiber without altering their original wavelengths.

This transmitting procedure may experience attenuation. To counteract this, operators always use optical amplifiers to boost signals, such as Erbium-Doped Fiber Amplifiers (EDFA).

When the light signals reach the receiving end, a DEMUX separates the combined light signals into individual wavelengths.

The separated light signals are then converted into electrical signals by devices with optical-to-electrical conversion capabilities, such as optical modules, switches, or ONUs/ONTs. These electrical signals are then processed and demodulated for further data handling.

This process efficiently completes the high-capacity transmission of optical signals using WDM technology.

Types of WDM Technology

To successfully transmit data using WDM systems, it is essential to control the wavelengths of each light signal, ensuring they do not interfere with each other, thus maximizing efficiency.

Coarse Wavelength Division Multiplexing (CWDM)

In the early stages of WDM technology development, due to technical limitations, signals were widely spaced, with wavelength intervals controlled at several tens of nanometers. This scattered form of wavelength division multiplexing is known as Coarse Wavelength Division Multiplexing (CWDM). CWDM is the first generation of WDM in optical communications, with a wavelength interval of 20nm and a range from 1270nm to 1610nm, covering 18 bands. The wide frequency range with widely spaced wavelengths is more suitable for short-distance transmission. When spectral efficiency is not a primary concern, CWDM offers a compact and cost-effective solution.

Dense Wavelength Division Multiplexing (DWDM) (CWDM)

As communication technology advanced, the focus shifted to long-distance transmission and the need for more diverse light signals in certain networks. This led to the compression of wavelength intervals to just a few nanometers, allowing more signal channels to be accommodated in a single fiber. This technology is known as Dense Wavelength Division Multiplexing (DWDM). DWDM has more diverse wavelength interval options, such as 1.6nm, 0.8nm, 0.4nm, and 0.2nm, and can accommodate 40, 80, or even 160 bands. However, the implementation and operational costs of DWDM are higher.

Future Trends in Optical Transmission Technology

Today, communication solutions are continuously exploring technologies that can accommodate higher fiber capacities. Wavelength Division Multiplexing (WDM) achieves capacity expansion by increasing the number of channels and the carrying rate of each channel. By reducing the channel spacing, more channels can be added. Currently, channel spacing has been reduced to 50GHz, allowing the C-band to carry up to 80 wavelengths. Extending to the L-band can further increase the signal carrying capacity, although commercial systems primarily use the C-band, and the path to extending the wavelength bands needs further development.

Many equipment manufacturers have shown great interest in methods to increase transmission rates, transitioning smoothly from 40G to 100G and overcoming physical transmission limitations.

The continuous development of WDM technology will make network deployments more diverse and simplified. Whether it’s data centers, large campuses, urban cellular networks, or long-distance networks connecting various cities, WDM technology allows operators to increase data capacity without laying additional cables, empowering the communication era.