Coarse Wavelength Division Multiplexing s one of the optical transport technologies that make use of the light wavelengths and fiber high band capacities along with SDH and DWDM technologies. CWDM is not the latest technology developed for optical transmission but it has its own advantages for choice in particular circumstances.
1.Simpler implementation and operation versus the DWDM implementation.
Simpler refers in this case to simpler optical hardware components necessary to implement the transmission system. Wavelengths spacing is much wider than in classical DWDM systems. Spacing is usually 20nm between lamdas instead of 50GHZ and 100GHZfrom DWDM. CWDM systems are using 8 or 16 or 32 lamdas versus 96 channels in DWDM systems. In 2002 the ITU standardized a channel spacing grid for use with CWDM (ITU-T G.694.2), using the wavelengths from 1270 nm through 1610 nm with a channel spacing of 20 nm. (G.694.2 was revised in 2003 to shift the actual channel centers by 1 nm, so that strictly speaking the center wavelengths are 1271 to 1611 nm..
Lower cost:
Fewer channels to transmit are reflecting in ⅓ fewer costs to implement. Transponders use a wider band to transmit channels being less sophisticated design. There is no need for optical amplifiers since the spacing between the channels are not making them suitable for EDFA amplification. The resulting distances are smaller, like 60Km for 2.5Gbit/s signal. Passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components such as bandpass filters and prisms. Many manufacturers are promoting passive CWDM to deploy fiber to the home. CWDM is based on uncooled distributed-feedback (DFB) lasers and wide-band optical filters. These technologies provide several advantages to CWDM systems such as lower power dissipation, smaller size, and less cost. The commercial availability of CWDM systems offering these benefits makes the technology a viable alternative to DWDM systems for many metro and access applications.
Easy to expand
Upgrading a 8 channel CWDM system to 16 channel system is easy  and is a matter of combining the mux/demux filters without the pain of adjusting the optical power or dispersion compensation DCM – modules like in case of DWDM. Low incremental cost: “Pay as you grow” Architecture. In DWDM systems, one connector can carry a whole cable’s-worth of traffic. If more than one connector is pulled and several incorrectly reconnected, the crap can truly hit the fan. Replacing, for instance, an amp (with DCM, OSC, and local connections) means everything disconnected has to be put back exactly as it was – or it might simply not work at all. Provisioning can be equally similarly disastrous. And these days, training exposure to these systems is minimal.Another benefit to the passive CWDM technology is that no configuration is necessary.The most complex step in CWDM integration is aligning and connecting the patch cables from the correct wavelength optic to the correct port on the multiplexers on each end of the link.
Specialized application evolve
CWDM – continues to evolve into specialized applications. Combination transport and optical routing or switches are being developed now. Add- on CWDM cards are being included in more transport devices as low cost options. Suppliers are continuing to drive down costs and increase capacity. CWDM and DWDM provides a unique “fit” and will complement not replace the other.
To sumarize the advantages of CWDM technology, it is worth to mention the following :
Lower power consumption – 20%
Smaller space requirements – 30%
Can use SMF or MMF cable
Can use LED or Laser’s for power
Smaller and cheaper wave filters
Cost saving on start up and expansion

Why Is CWDM so Popular?

WDM (wavelength division multiplexing) technology transmitting multiple signals on a single optical fiber by using different wavelengths to carry each signal has been used since 1980s. In the middle of 1990s, dense wavelength division multiplexing (DWDM) enabled carriers to extend the capacity of the SONET/SDH rings in the network core, without installing new fiber. As the development of data service, MAN has become a hot topic of network construction. However, DWDM system brings telecom operators very high costs in MAN construction. So the other kind of WDM technology, CWDM (coarse wavelength division multiplexing) emerged.
CWDM has fewer channels than DWDM. The energy from the lasers in a CWDM system is spread out over a larger range of wavelengths than is the energy from the lasers in a DWDM system. CWDM has many advantages like low cost, low power consumption and small volume. As an economical and practical short-distance WDM transmission system, CWDM becomes more and more recognized by people in many MAN applications just as follows.
Fiber Exhaust Relief
Fiber exhaust which means lack of network capacity occurs in metropolitan networks. CWDM is a simple and cost-effective way for people to solve fiber exhaust. By using CDWM, new services can be added over an existing single optical fiber. So to increase optical network capacity, people don’t need to replace existing equipment with higher bit rate transmission rate and install new fibers. Otherwise, it will cost too much because installing new fiber is a costly venture in metropolitan areas.
Low-cost WDM Deployments
CWDM system with reduced channels is beneficial for carriers in the metro-regional areas. It supports 4-channel configuration. Systems with 4 channels can quadruple the available capacity over an existing network segment, while offering a lower firstin deployment cost than an 8-channel system. For carriers, they should pay attention to two important points including cost and scalability when they need to upgrade to 8 channels systems. So CWDM is a good choice.
Central Office to Customer Premise Interconnection
CWDM is a good fit for metro-access applications such as Fiber to the Building (FTTB). An 8-channel CWDM network can deliver 8 independent wavelength services from the Central Office to multiple business offices located in the same building.
Due to the low cost, simplicity and scalability features of the latest products such as CWDM modules, CWDM systems is a good choice for overbuilding with Next Generation SONET, DWDM, and proprietary solutions. CWDM is becoming more and more popular among carriers who need to upgrade their networks to accommodate current of future needs while minimizing the use of valuable fiber strands especially in the metropolitan areas.

CWDM Solutions Offered by

As broadband has unveiled a new world for subscriber, full of advanced capabilities and faster speeds. Your challenge is to meet their demands without compromising your budget. Because of its distance, speed and bandwidth potential, fiber optics has become the choice for many service providers. Fiber optic connections typically requires two strands of fiber – one for transmitting and one for receiving signals. But how to do if you need to add services or customers, but you’ve exhausted your fiber lines?
Thanks to CWDM, coarse wave division multiplexing (CWDM) is a method of combining multiple signals on laser beams at various wavelengths for transmission along fiber optic cables. The number of channels is fewer than in dense wavelength division multiplexing (DWDM) but more than in standard WDM.
CWDM has many advantages over DWDM technology in terms of system costs, set-up, maintenance, and scalability. CWDM is a technology which multiplexes multiple optical signals on a single fiber optic stand by using different wavelengths, or colors, of laser light to carry the different signals.
Typical CWDM solutions provide 8 wavelengths capacity enabling the transport of 8 client interface over the same fiber. However, the relatively large separation between the CWDM wavelengths allows expansion of the CWDM network with an additional 44 wavelengths with 100GHz spacing utilizing DWDM technology, thus expanding the existing infrastructure capacity and utilizing the same equipment as part of the integrated solution.
A single outgoing and incoming wavelength of the existing CWDM infrastructure is used for 8 DWDM channels multiplexing into the original wavelength. DWDM Mux Demux and optical amplifier if needed.
The typical CWDM spectrum supports data transport rates of up to 4.25Gbps, CWDM occupies the following ITU channels: 1470nm, 1490nm, 1510nm, 1530nm, 1550nm, 1570nm, 1590nm, and 1610nm, each separated from the other by 20nm. PacketLight can insert into any of the of the 4 CWDM wavelengths (1530nm,1550nm,1570nm and 1590nm), a set of additional 8 wavelength of DWDM separated from each other by only 0.1nm. By doing so up to 4 times, the CWDM network capability can easily expand by up to 28 additional wavelengths.
With’s compact CWDM solutions, you can receive all of the above benefits and much more (such as integrated amplifiers, protection capabilities, and integration with 3rd party networking devices, etc.) in a cost effective 1 U unit, allowing you to expand as you grown, and utilize your financial as well as physical resources to the maximum. provides all the component involved in the process, such CWDM MUX DWMUX, CWDM OADM, even CWDM SFP transceivers.

What You Need to Know When Using 10G over CWDM


Both Passive CWDM and DWDM have been viable solutions in the telecommunications industry, but now, 10G Ethernet is appearing to be the most preferred solution over CWDM, everyone is migrating to the use of 10G Ethernet. This encourages many engineers to figure out how they ought to adjust their new designs to support the transition from 10G to CWDM. If you’re one of these designers who’s attempting to navigate the transition, the following is what you need to know.
Bandwidth Exts are Easier
In past years, designers who want to increase or improve their bandwidth could achieve this easily over a single or duplex mode fiber. During this period, the 1G Ethernet and CWDM solutions were sufficient, and the only limiting element was the power budget of the optical transceiver or the attenuation of your fiber. That it was possible to transmit up to 200 kilometers and utilize just a 1G Ethernet when designers preferred cheap CWDM.
Now, many people are considering the 10G Ethernet solutions, and that’s why it’s necessary to understand how everything will differ when using 10G over CWDM. When intending to migrate to 10G, you need to know the fiber type. For the dispersion and attenuation calculation, every designer need to know the recommended parameters from ITU-T and understanding the vendor and product kind of the fiber could also help. Remember that the physical fiber will work better than the standards claim most of the time.
Chromatic dispersion is referred to as the time variance of a single pulse of a signal. To summarize, chromatic dispersion is “the spreading of a light pulse per unit source spectrum width in an optical fibre due to the various group velocities of the different wavelengths composing the source spectrum” or in layman’s terms, “the signal is stretched on the fiber transmission path due the dispersion characteristics of the transporting fiber.”
Chromatic dispersion always exists, but the higher the link speed is, the greater important it becomes. For instance, a wavelength of 1310nm have a 0 ps/nm chromatic dispersion and 5, 25 dB fiber attenuation. In comparison, a wavelength of 1610 nm have a 330 ps/nm chromatic dispersion and a 3,45 dB fiber attenuation.
CWDM Over DWDM 10G is Cost-Effective
Designers should bear it in mind that CWDM implementation is more cost effective than passive DWDM infrastructure. These solutions will be more expensive because DWDM lasers cost more. DWDM lasers are essentially DFB lasers which are cooled, however, they are recommended as they contain the longevity that are required in these solutions. If you would like transmit a signal over a large distance, you should think about large metro ring topologies.
Though 10GBASE DWDM is more expensive, it’s become the first choice because users have started to consider the costs after dividing it over the quantity of customers served. Some customers are more cost-conscious and have lower bandwidth capacity requirements; so, the cheap CWDM infrastructure will make more sense.
Remember that the new 10GBASE DWDM services is usually added over the same fiber. This will enhance the support of the initial CWDM infrastructure capacity by 4 times. This is irresistible to many designers.
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