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Comparison Between CWDM and DWDM

With the rapid development of telecommunications, the demand for cable capacity is stronger more than ever. WDM (Wavelength Division Multiplexing) will be the preferred method to meet the needs. WDM systems are divided into different wavelength patterns, conventional/coarse (CWDM) and dense (DWDM). This post aims to make a comparison between CWDM and DWDM.

WDM and It’s Working Principle

Wavelength Division Multiplexing is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity. A WDM system uses a multiplexer at the transmitter to join the signals together, and a demultiplexer at the receiver to split them apart. With the right type of fiber it is possible to have a device that does both simultaneously, and can function as an optical add-drop multiplexer.

CWDM is the technology of choice for cost efficiently transporting large amounts of data traffic in telecoms or enterprise networks.

DWDM is an optical technology used to increase bandwidth over existing fiber optic backbones.

Comparison between CWDM and DWDM will be illustrated from the following aspects:

  • Channel Numbers: DWDM can fit 40-plus channels into the same frequency range which is twice of CWDM can fit. CWDM is used more often than DWDM due to the cost factor. Now that cabling and transmission has become more affordable, DWDM takes place of CWDM. CWDM is defined by wavelengths, while DWDM is defined in terms of frequencies.
  • Modulated laser: Unlike DWDM deploys cooled distributed-feedback (DFB), 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.
  • Transmission Distance: Another major difference between the two is that DWDM is designed for longer haul transmission, by keeping the wavelengths tightly packed. It can transmit more data over a significantly larger run of cable with less interference than a comparable CWDM system. If there is a need to transmit the data over a very long range, the DWDM will likely be the priority in terms of functionality of the data transmittal as well as the lessened interference over the longer distances that the wavelengths must travel. CWDM cannot travel long distances because the wavelengths are not amplified, and therefore CWDM is limited in its functionality over longer distances. Typically, CWDM can travel anywhere up to about 100 miles (160 km), while an amplified dense wavelength system can go much further as the signal strength is boosted periodically throughout the run. As a result of the additional cost required to provide signal amplification, the CWDM solution is best for short runs that do not have mission critical data.

From the comparison above, we can know both the benefits and drawbacks of CWDM and DWDM.  If the transmission distance is short and cost is low, then CWDM may be your first choice. On the contrary, you can consider DWDM. For more information about CWDM and DWMD, you can visit Fiberstore.

Advanced Optical Components – WDM Multiplexer

WDM Multiplexer is a device that uses Wavelength Division Multiplexing (WDM) technology to combine different optical wavelengths from two or more optical fibers into just one optical fiber. This combining or coupling of the wavelengths can be very useful in increasing the bandwidth of a fiber optic system. WDM multiplexers are used in pairs: one at the beginning of the fiber to couple the inputs and one at the end of the fiber to decouple and then route the separated wavelengths into separate fibers. A WDM multiplexer can be thought of as an optical fiber highway; the highway can support a very large bandwidth, thus increasing the system’s capacity.

Each channel in a WDM multiplexer is designed to transmit a specific optical wavelength. The multiplexer operates very much like a coupler at the beginning of the optical fiber and as a filter at the end of the optical fiber. For example, an 8-channel multiplexer would have the ability to combine eight different channels or wavelengths from separate optical fibers onto one optical fiber. Again, to take advantage of the enormous bandwidth at the end of the optical fiber, another multiplexer (demultiplexer) will recover the separate wavelengths. The figure below shows a simple WDM system composed of multiple light sources, a WDM multiplexer or combiner that combines the wavelengths into one optical fiber, and a WDM demultiplexer or optical splitter that separates the wavelengths to their respective receivers.

Simple WDM System

Types of WDM Multiplexers

  • CWDM & DWDM Multiplexers

WDM multiplexers are available in a variety of sizes, but will most commonly be found with 2, 4, 8, 16, 32, and 64 channels configurations. The types of multiplexers are wideband (or crossband), narrowband, and dense. Wideband or crossband multiplexers (CWDM Multiplexer) are devices that combine a broad range of wavelengths, such as 1310 nm and 1550 nm. A narrowband multiplexer will combine multiple wavelengths with 1000 GHz channel spacing. A dense multiplexer combines wavelengths with 100 GHz channel spacing. Here shows a basic wideband or crossband WDM system.

Basic Wideband or Crossband WDM System

Narrowband WDM (DWDM) systems have channels spaced 1000 GHz, or approximately 8 nm, apart. Here is a figure that shows a basic narrowband WDM system.

Basic Narrowband WDM System

The industry standard on the Dense Wavelength Division Multiplexing Multiplexers (DWDM Multiplexer), as recommended by the International Telecommunications Union (ITU), is 100 GHz or approximately 0.8 nm channel spacing. There are C-band, S-band, and L-band DWDM multiplexers. The C-band is the 1550 nm band which uses wavelengths from 1530 to 1565 nm. The S-band uses wavelengths from 1525 to 1538 nm, and the L-band uses wavelengths from 1570 to 1610 nm.

The closer the channels are spaced together, the higher the number of channels that can be inserted into a band. Currently a spacing of 50 GHz is available (the 50 GHz DWDM multiplexers are generally with 64, 80, 88, 96 channels). It is important to note that as the spacing or the width of each channel decreases, the smaller the spectral width becomes. This is relevant because the wavelength must be stable or sustainable long enough not to drift into an adjacent channel. Besides having a very narrow spectral width, the laser transmitter cannot drift (it must out- put the same wavelength at all times). If the laser transmitter’s output wavelength changes even a few tenths of a nanometer, it could drift into the next channel and cause interference problems.

  • Unidirectional & Bidirectional WDM Multiplexers

There are different configurations of WDM multiplexers. Everything we have covered up to this point describes a unidirectional WDM system. The Unidirectional WDM Multiplexer is configured so that the multiplexer only connects to optical transmitters or receivers. In other words, it allows the light to travel in only one direction and provides only simplex communication over a single optical fiber. Therefore, full-duplex communications require two optical fibers.

A WDM multiplexer that is designed to connect with both transmitters and receivers is called bidirectional (BiDi); in essence, the BiDi WDM Multiplexer is designed for optical transmission in both directions using only one optical fiber. Two channels will support one full-duplex communication link. Here is a figure that shows two BiDi WDM multiplexers communicating over a single optical fiber.

2-Channel BiDi WDM System

Tips for Using WDM Multiplexers

As with any other device that is added to a fiber optic network, there are factors that must be considered. As losses are a factor that must be taken into account, you should remember that the greater the number of channels, the greater the insertion losses when using WDM multiplexers. Other specifications to keep in mind when using WDM multiplexers are isolation, PMD, and the spectral bandwidth.


WDM multiplexers are widely used devices which provide a way to utilize the enormous bandwidth capacity of optical fiber without the expense of using the fastest laser transmitters and receivers. Just think about it: an 8-channel WDM system using directly modulated 2.5 Gbps laser transmitters carries twice as much data as a single indirectly modulated 10 Gbps laser transmitter. WDM systems allow designers to combine modest performance parts and create an ultra-performance system. WDM systems deliver the most bang for the buck!

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CWDM/DWDM technical overview

CWDM is an optical technology for transmitting up to 16 channels, each in a separate wavelength or color, over the same fiber strand. The CWDM solutions help enable enter-prises and service providers to increase the bandwidth of an existing Gigabit Ethernet optical infrastructure without adding new fiber strands. Unlike DWDM, which can transmit up to 160 channels on the same fiber by tightly packing them, CWDM technology relies on wider spacing between channels. this design makes CWDM a relatively inexpensive technology for transmitting multiple gigabit-per-second signals on a single fiber strand as compared with DWDM because it can support less-sophisticated, and therefore cheaper, transceiver designs. In the point-to-point configuration shown in Figure 1-1, two rndpoints are directly connected through a fiber link. The ITU has standardized a 20-nm channel-spacing grid for use with CWDM, using the wavelengths between 1310 nm and 1610 nm. Most CWDM systems support eight channels in the 1470-to 1610-nm range. The Fiberstore CWDM Gigabit Interface Converter small form-factor pluggable(SFP) solution allows organizations to add or drop as many as eight channels (Gigabit Ethernet or Fibre Channel) into a pair of single-mode (SM) fiber strands. As a result, the need for additional fiber is minimized. You can create redundant point-to-point links by adding or dropping redundant channels into a second pair of SM fiber strands.

9     Figure 1-1


CWDM Technical Overview

CWDM Multiplexer is achieved thruogh special passive (nonpowered) glass devices known as filters. The filters act as prisms, directing lights from many incoming and outgoing fibers (client ports) to a common transmit and receive trunk pots. Optical multiplexing in a ring with CWDM networks is supported with optical add/drop multiplexers (OADM). OADMs can drop off one or more CWDM wavelengths at a specific location and replace that signal with one or more diferent outbound signals. The Fiberstore CWDM GBIC/SFP solution has two main components: a set of eight different pluggable transceivers (Fiberstore CWDM GBICs and CWDM SFP), and a set of different Fiberstore CWDM passive multiplexers/demultiplexers or OADMs. Both the transceivers and the passive multiplexers are compliant with the CWDM grid defined in the standards. CWDM can be used by enterprises on leased dark fiber to increase capacity (for example, from 1 Gbps to 8 Gbps or 16 Gbps) over metro-area distances. One problem with CWDM is that the wavelengths are not compatible with erbium-doped fiber amplifier (EDFA) technology, which amplifies all light signals within their frequency range. CWDM supports up to a 30 -dB power budget on an SM fiber. This restricts the distances over which CWDM may be used. CWDM supports distances of approximately 60 miles (100km) in a point-to-point topology and about 25 miles (40 km) in a ring topology. in some areas, service providers use CWDM to provide lambda or wavelength services. A lambda service is where a provider manages equipment and multiplexes customer traffic onto one or more wavelengths for a high-speed connection, typically bet ween two or more points.

DWDM Technical Overview

DWDM is a core technology in an optical transport network. The concepts of DWDM are similar to those for CWDM. However, DWDM spaces the wavelengths more tightly, yielding up to 160 channels. The tighter channel spacing in DWDM requires more sophisticated, precise,and therefore more expensive transceiver designs. In a service provider is backbone network, the majority of embedded fiber is standard SM fiber with high dispersion in the 1550-nm wubdiw, DWDM supports 32 or more channels in the narrow band around 1550 nm at 100-GHz spacing, or about 0.8 nm, as illustrated in Figure1-2. Because of the EDFA compatibility of the wavelenths used, DWDM is also available over much longer distances than CWDM and supports metropolitan-area network (MAN) and WAN applications. In practice, signals can travel for up to 75 miles (120 km) between amplifiers if fiber with EDFA is used. At distances of 375 miles (600 km) to 600 miles (1000 km), the signal must be regenerated.

Figure 1-2

DWDM can be used as a high-speed enterprise WAN connectivity service. Typical DWDM uses include connectivity between sites and data centers for example 1-, 2-, or 4- Gbps Fiber channel; IBMfiber connectivity (FICON) and Enterprise System Connection(ESCON); and Gigabit and 10 Gigabit Ethernet. Protection options include client-side safeguards using rerouting, an optical splitter that allows the signal to go both ways around a ring or line-card-based protection that detects boss of signal and wraps.

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Detailed description of CWDM module and system

CWDM is actually brief with regard to Rough Wavelength Department Multiplexing. Initially, the word “coarse wavelength department multiplexing” had been pretty universal, as well as designed a variety of points. Generally, this stuff discussed the truth that the option associated with funnel spacings as well as rate of recurrence balance had been so that erbium doped dietary fiber amplifiers couldn’t end up being employed. Before the fairly current ITU standardization from the phrase, 1 typical which means with regard to rough WDM designed 2 (or even much more) indicators multiplexed on to just one dietary fiber, exactly where 1 transmission is at the actual 1550 nm music group, and also the additional within the 1310 nm music group.
CWDM quests consist of CWDM mux/demux component as well as CWDM DWDM component. The most popular settings associated with CWDM mux/demux component is actually 2CH, 4CH, 8CH, 16CH, 18CH CWDM MUX component. 3 Solitary dietary fiber or even twin dietary fiber link with regard to CWDM Mux/demux can be found. Appropriately, they’ve 2 essential features natural within techniques using CWDM optical elements that permit simpler and for that reason additionally less expensive compared to within DWDM techniques. CWDM really is easy when it comes to system style, execution, as well as procedure. CWDM works together with couple of guidelines that require optimisation through the person, whilst DWDM techniques need complicated information associated with stability associated with energy for each funnel, that is additional complex whenever stations tend to be additional as well as eliminated or even when it’s utilized in DWDM systems diamond ring, particularly when techniques include optical amplifiers.
WDM (Wavelength Department Multiplexing) is really a method, that runs on the distinctive home associated with fiber-optics. This particular home enables the actual mixture of several indicators on to just one follicle associated with dietary fiber. Every transmission is actually possessed through an additional wavelength, associated with gentle. Because 1 wavelength doesn’t have impact on an additional wavelength, the actual indicators don’t conflict. As well as CWDM (Rough wavelength department multiplexing) is often a technologies that multiplexes several optical indicators for any moving extravagant dietary fiber optic follicle by using various wavelengths, or even colours, associated with laser beam gentle to keep the various indicators. By using bidirectional marketing communications greater than a solitary follicle associated with dietary fiber, system supervisors may recognize the multiplication impact inside the capability of those obtainable dietary fiber national infrastructure.
CWDM quests carry out 2 features. Very first, these people filtration system the actual gentle, making sure basically the required wavelengths are utilized. 2nd, these people multiplex or even demultiplex several wavelengths, which may be utilized on only one dietary fiber hyperlink. The actual distinction is within the actual wavelengths, which are utilized. Within CWDM room, the actual 1310-band along with the 1550-band tend to be split in to scaled-down rings, every just 20-nm broad. Inside the multiplex procedure, the actual several wavelength rings tend to be mixed on to only one dietary fiber. Within the demultiplex procedure, the actual several wavelength rings tend to be divided from the solitary dietary fiber. Usually, the CWDM system requires 2 types. The point-to-point program links 2 areas, muxing as well as demuxing several indicators for any moving extravagant dietary fiber. The cycle or even multi-point program links several areas, usually utilizing Add/Drop quests.

Video multiplexer using high speed amplifier

In the past few years, the number of video sources connected to a single display has increased steadily, make the video signal switching must in most video system. In a typicaly home entertainment systems, for example, a set-top box (STB) or digital video recorder (DVR) cable or statellite TV, VCR, DVD players, a video game console, and a PC all feed a single display. The ability to switch multiple video sources to a single display extends to cars as well, where video sources include the vehicle entertainment system, rearview camera, DVD player, navigation system, and auxiliary video input.

Traditional CMOS multiplexers and switches suffer several disadvantages at video frequencies, where their on resistance introduces distortion, degrades differential gain and phase performance, and interacts with the terminal resistor to the attenuation of the incoming video signal and affect intensity. System designers to solve this problem by adding external buffer added gain, increasing the drive capability.

Video multiplexing can be simplified by using high speed video amplifiers with a disable mode. When the semiconductor optical amplifiers is disabled, its output stage into a high impedance state. This is different from their low power consumption mode, greatly reduces the power consumption, but leave the state of the output stage is undefined.

High-speed video amplifiers have all the key features required to make them ideal for this function. Their high input impedance does not affect the characteristic impedance of the transmission line, thus allowing back termination. Because they are video amplifiers, they have inherently good video specifications, including differential gain and phase, slew rate, bandwidth and 0.1-dB flatness.

In a mux configuration, the disabled channels present a high-impedance load to the single active channel. The gain setting and feedback resistors load the active amplifier, but their values are large compared to the 150-ohm video load, so their effect is negligible.

3:1 Video Multiplexer

Fiber optic amplifier is used to encodes the multi channel video signals and convert them to optical signals to transmit on optical fibers. The ADA4853-3 has independent disable controls, making it suitable for use as a low-cost 3:1 buffered -output video mux. Its output impedance is greater than 2-kohms at 10 MHz, so the amplifier outputs can be connected to form a 3:1 mux with excellent switching behavior and great isolation characteristics. Operating on a single 5-V supply, the configuration shown in Figure 1 provides 14-MHz bandwidth (0.1-dB), gain of +2, and 58-dB off- channel isolation at 10 MHz. Its 10-s channel-to-channel switching time supports CVBS analog video applications.(Related articles:cwdm multiplexer)

High-Performance 2:1 Video Multiplexer

Figure 2 shows a high-performance 2:1 mux. The two input amplifiers are configured as unity gain followers, while the output amplifier is set for a gain of +2. The ability to shut-down both stages allows this mux to achieve the excellent input-to-output off-isolation shown in Figure 3. Switching time in this configuration is 45 s.

High-speed video amplifiers with a single disabled needle is very suitable for simple structure, low cost video multiplexers and switches for compound and high resolution video. They are the ideal replace CMOS switch, it is more cost effective than video multiplexer. Be sure to consider using high-speed video amplifiers if your system requires video switching function.

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