What is Wavelength Division Multiplexing (WDM)?
Wavelength Division Multiplexing, or WDM is a way of increasing bandwidth in fibre optic networks by allowing for multiple transmissions over a single fibre. This is a simple and cost-effective way of optimising the potential of an existing or new network, reducing complexity in wireless systems. It currently allows for up to 80 simultaneous data streams per fibre. The passive nature of WDM allows for easy implementation as there is minimal interference with the existing system. In simple terms, a WDM system consists of 4 elements:
- Transceivers for sending and receiving data
- Fibre Patch Cables connecting transceivers and multiplexers
- Multiplexers/Demultiplexers (MUX/DEMUX)
- Dark fibre cables for data transmission
What are Multiplexers/Demultiplexers (MUX/DEMUX)
Multiplexers (MUX) and Demultiplexers (DEMUX) are the hardware used to manage multiple data signals within WDM systems. The MUX collates the light signals sent by fibre optic network transceivers and sends them down the dark fibre cable and across the network. On the other side, the DEMUX reads the incoming signal and splits it back across multiple channels.
CWDM vs DWDM
There are two different types of WDM systems, both with different characteristics and uses – Coarse WDM (CWDM) and Dense WDM (DWDM).
CWDM
- Less than 8 input wavelengths per fibre
- Short range communication of up to 80km
- Lower bandwidth capacity
- Compact and cost effective
CWDM modules have a large wavelength span of 20nm between channels and operate within the 1270nm – 1610nm wavelength range. This allows for up to 18 channels which limits the data capacity compared to DWDM modules that can accommodate many more. Due to this, CWDM is generally used in less demanding short to medium range applications, but can be much more cost effective in these scenarios.
DWDM
- More than 8 wavelengths of light per fibre
- Long range communication of over 80km
- High bandwidth capacity
- High cost of implementation and operation
DWDM modules commonly operate in the C-Band wavelength range which is approximately 1530nm – 1565nm and have much smaller wavelength spans. This tight spacing allows for 40+ channels within the C-Band range with even further capacity when utilising the adjacent L-Band range (1565nm – 1625nm). The narrower channel spacing allows for more precise control over each wavelength which is a key factor in DWDM’s distance capabilities. Additionally, this form of WDM has the capacity to be amplified to reach ranges of hundreds, or even thousands of kilometers. These factors mean that DWDM is more suitable for complex and demanding long range data transmissions.
However, lasers can lose their wavelength accuracy when heated up which can be an issue for DWDM hardware. To help prevent this, the lasers are cooled which consumes more power and often leads to higher manufacturing costs for DWDM products.
Dark Fibre Cables
There are two types of dark fibre cable that can be used to connect the MUX and DEMUX within a system – single fibre or a dual fibre pair.
With single fibre, transmission and reception of data is done on the same fibre by using different wavelengths for transmission and receival of data. On the other hand, with a dual fibre pair, one fibre is used for transmission of data, and the other to receive data. This means that data streams can have the same wavelength without interfering with each other.
Although dual fibre – the most common dark fibre infrastructure – generally allows for higher data capacity, using a bidirectional single fibre can have its advantages. For example, it uses less fibre resources and can be cheaper to implement.
Tunable mux/demux
A tunable WDM transceiver is able to dynamically tune to different wavelengths within a certain range to suit the needs of the network. This can be done manually, but is usually automatic, responding to specific network conditions or a centralised system control. Within a fixed WDM system, the device is chosen depending on the wavelength of the network node it will be used in. However, tunable WDM modules can be used in multiple wavelength ports due to their adaptability.
Tunable devices are useful for complex networks that may often require reconfiguration or device replacement, accommodating scalability and complexity requirements common in modern networks without the need for new hardware.
Although more expensive, tunable WDM devices can save money in the long run as they can adapt to new network requirements. Additionally, they can be useful in streamlining stock reserves as spares for a range of transceiver modules as opposed to needing lots of different wavelength specific units. This simplifies inventories, far reducing the necessary backup stock.
Custom filtering options
Flat top and gaussian filters are used in WDM modules to determine how light is filtered through the cable and the shape of the beam.
Flat top
- Flat, rectangular spectral profile
- Uniform insertion loss
- Higher cost
Flat top filters let light through evenly, blocking sharply at the edges leading to extremely precise beams. Due to this, they are useful in DWDM modules where channels are tightly packed together as they are unlikely to leak light into other channels.
Gaussian
- Spectral profile peaks at the channel centre, fading off in a bell shape
- Lower insertion loss at the channel centre
- Lower cost
Light from a gaussian filter is not even, tapering off at the sides which can cause light to ‘leak’ into adjacent channels causing interference. Due to this, they are commonly used in less demanding WDM equipment with spaced out channels to avoid crosstalk between data streams.
Thin Film Filters
While flat top and gaussian filters affect how light passes through the fibre, thin film filters determine what light (and subsequently what data) is filtered through. They use multiple layers of dielectric film of varied thickness and refractive indices to isolate specific light wavelengths. This is pivotal in WDM systems and is used to both combine (multiplex) and separate (demultiplex) light signals travelling through the fibre.
Thin film filters are a compact, stable and reliable component in WDM systems, carefully designed to allow precise wavelengths of light through, while reflecting the others. They are also used in add/drop multiplexing to isolate parts of a data stream to be added to, or dropped from the network.
Industry Applications
Multiplexers and Demultiplexers are integral in many high performance networks, especially as data and bandwidth requirements are increasing. Their unique ability to manage many data streams efficiently make them critical devices across a variety of industries including:
- Data Centres
- Telecommunications Networks
- Enterprise Networks
- Broadcasting and Media Production
- Military and Aerospace
- Healthcare and Medical Imaging
- Industrial Automation
- Transportation and Intelligent Traffic Systems
- Utilities and Energy Grids
Find out more about real world multiplexing applications here.
Summary
In summary, Wavelength Division Multiplexing is an efficient and cost-effective way to expand, upgrade and future-proof networks. As digital technologies are rapidly evolving and become exponentially more complex, the bandwidth (and subsequently energy and hardware) requirements are ever increasing. This demands more efficient and innovative technologies like WDM to make the most out of both old and new infrastructure.
ATGBICS Solutions
In today’s fast-paced digital landscape, effective bandwidth management is critical to maintaining a competitive edge. At ATGBICS, we provide high-performance CWDM and DWDM MUX/DEMUX solutions, designed to help datacom, enterprise networks, and industries such as telecom, defence, industrial automation, and healthcare optimise their networks with precision and reliability.
Our CWDM range supports up to 18 channels (1271nm – 1611nm), and our DWDM range offers up to 96 channels (1530nm – 1585nm), facilitating both single and dual bidirectional fibre transmissions.
By choosing ATGBICS MUX/DEMUX products, you can:
- Maximise large capacity data transmission between sites
- Utilise existing fibre infrastructure
- Benefit from flexibility, cost-effectiveness, dependability and low insertion loss
- Ensure high security and wavelength routing
Our CWDM and DWDM compatible transceivers support SFP, SFP+, SFP28, and QSFP28 form factors, with tunable options available.
Don’t miss the opportunity to enhance your network’s performance. Explore our full range of MUX/DEMUX solutions, or get in touch with us to discuss your specific requirements.
