Introduction to CWDM Technology

CWDM stands for Coarse Wavelength Division Multiplexing which utilizes multiplexer to  combine multiple optical signals at different wavelengths on one optic fiber, and then uses de-multiplexer to separate those hybrid optical signals at their own wavelengths at the receiver. CWDM transmits optical signals using 18 channels with the wavelengths between 1270 nm and 1610 nm with a channel spacing of 20 nm.

CWDM Technology

CWDM is an effective way to meet the rapidly increasing demand of bandwidth in transmission network and it can provide a cost-effective solution for high capacity in metropolitan area network and local area network. For example, when transmitting the signals at the same speed on the same optical fiber, the bandwidth provided by a typical 8-chanel system is eight times larger than that of a traditional SONET/SDH system. Compared with DWDM technology, CWDM is specially designed for short-distance network application with a high performance-price ratio, gradually becoming the focus of telecommunication industry.

CWDM system regenerates the optical signals at each node without using optical amplifier. Optical signal regeneration refers to the process that converting the optical signal to electric signal, and then converting the electric signal back to optical signal by using OEO (optical-electric-optical) transponder. Since all channels are regenerated at each node in CWDM system, and the optical link power budget has nothing to do with the number of channel among nodes, the design of network is simplified.

CWDM Multiplexer, CWDM De-multiplexer and Transponder

CWDM Applications

Due to the technical limitation, CWDM is usually used in metropolitan area network and access network. It has two main functions. One function is to use each wavelength channel to transmit different optical carrier signals at different rates. And the other function is to split optical carrier signals into multiple low-speed signals for saving cost.

CWDM in LAN and SAN Connection

CWDM system has a variety of network topology, such as point-to-point, ring, etc. Among them, the ring topology is equipped with self-protection and self-repair function, including link breaking protection and node fault separation. The ring link and point-to-point link of CWDM are very suitable for interconnection between scattered nodes in LAN (local area network) and SAN (storage area network). With low cost, low power consumption, small size and many other advantages, CWDM system has been widely used in LAN and SAN.


CWDM in 10 Gigabit Ethernet

With low implementation cost, relatively simple installation and maintenance, Ethernet has been widely used in metropolitan area network and access network. IEEE 802.3 Ethernet standards realized a rapid development of bandwidth from 10 Mbit/s to 100 Mbit/s to 10 Gbit/s. Applying CWDM technology to Gigabit Ethernet can greatly increase network capacity. Compared with TDM (Time Division Multiplexing), CWDM system is characterized by better flexibility and  scalability. For metropolitan services, the flexibility, especially the speed and the ability to expand as the business grows, is very important. Using CWDM technology can open the business for the user within a day or a few hours. And with the increasing of business, capacity expansion can be realized by inserting a new OTU board. Therefore, CWDM obtains more and more applications in telecommunication, broadcasting, enterprise network, campus network and other fields.

CWDM in PON (Passive Optical Network)

CWDM technology is also used in PON, a kind of point-to-multiple optical communication way. Combined with PON, each individual wavelength channel of CWDM system can serve as virtual optical link of PON, realizing the bandwidth data transmission between central node and multiple scattered nodes. CWDM and PON system can assign different wavelengths for video signal, data and voice signal to realize single fiber bidirectional transmission.



The very wide channel spacing of CWDM technology allows for the use of cheaper CWDM network components, such as uncooled lasers or lower-quality multiplexers and de-multiplexers. And CWDM technology is a very attractive option in metropolitan networks that require additional bandwidth without overbuilding the infrastructure.


Know More About WDM System

A WDM system uses a multiplexer at the transmitter to join the several signals together, and a de-multiplexer 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.

Followings are some required equipment to build a WDM system.


Multiplexer is a device that multiplex a number of optical signals at different wavelengths onto a single optical fiber.


Contrary to multiplexer, de-multiplexer is used to de-multiplex or split hybrid optical signals at different wavelengths and makes them transmitted at their own wavelengths on different optical fibers.


OADM stands for Optical Add-Drop Multiplexer which is a device used in WDM system. Its function is to selectively transmit and receive wavelengths on some channels without affecting the transmission on other channels.


FWDM stands for Filter-Based Wavelength Division Multiplexer which is a kind of multiplexer based on the Thin Film Filter (TFF) technology. FWDM can combine or separate light at different wavelengths in a wide wavelength range. It is commonly used in Erbium-Doped Fiber Amplifier, Romam amplifier and WDM optical network.

Compact WDM

As the name suggests, it is a kind of multi-channel WDM product. It is relatively small in size, so it is able to provide more channels in the application of FOSC (Fiber Optic Splice Closure), splice tray or splice holder. Compact WDM adopts free-space multiple bounce technology which refers to light is reflected directly from one filter element to the next filter, instead of parallel into the optical fiber. In addition, using bend insensitive fiber can combine individual TFFs with a multi-channel product.

Banded Skip Filter

Banded skip filter is applied to BWDM (Bandpass Wavelength Division Multiplexer). This type filter has wide pass band which contains multiple channels. For example, DWDM Red/ Blue C-band Filter is used to combine or separate Red and Blue band wavelength signals in C-band DWDM system and high-power amplification system. It works like ordinary FWDA, with the only difference that the wavelengths are combined in WDM system while separated in Red/Blue Filter.

Ports on WDM Equipment

ports on wdm equipment

Common Port

Common port is the connection point of multiple channels in WDM device. For multiplex product, multiple channels are transmitted from the common port; while for de-multiplex product, multiple channels are received at the common port.

Express or Upgrade Port

For CWDM product, there usually is either express port or upgrade port, but both of them will not exit on the same one WDM product. The express port or upgrade port on CWDM multiplexer or de-multiplexer is used to add, drop or pass through new channels. Those new channels can cascade two CWDM multiplexers or de-multiplexers, so the channel capacity is doubled in the original fiber optic link.

For DWDM product, the function of express port is to add, drop or pass through C-band DWDM channels which are not used, referring to channels whose band is between 1530 nm and 1565 nm. If the DWDM product has an upgrade port, then the express port is usually used for new channels outside C-band, such as most CWDM channels.

1310 nm Port

1310 nm port is a kind of port with wide band which is used for adding other special CWDM wavelengths. For example, when the eight-channel channel uses wavelengths between 1470 nm to 1610 nm, it may need the 1310 nm port at the same time. The 1310 nm port is usually used in some traditional networks and sometimes as a return path. If an existing traditional network is using 1310 nm port, all the optical fibers have already been fully occupied, and ways to increase network capacity are wanted, then other CWDM wavelengths can be added into the fibers while allowing the use of 1310 nm. What’s more, 1310 nm port can support LR optics, LX optics.

1550 nm Port

It is similar to 1310 nm port and can transmit traditional 1550 nm optical signals. Also, it can support ER optics, ZR optics, LX optics, ZX optics and so on.

Monitor Port

Monitor port is used to monitor or test the power signal which is multiplexed by CWDM but not de-multiplexed. Monitor port is usually connected with testing or monitoring device, such as power meters or network analyzers. If the signal changes or fails to to be transmitted, the network administrator can use monitor port to detect fault without interrupting the existing network.


The traffic volume of telecommunication networks is rapidly increasing, and this trend will clearly continue into the next century. Therefore, it is important to build network systems which can be easily upgraded to cope with increases in traffic volume. Because WDM system has the merits of high-capacity, high-speed, low-cost and good-upgradability, it will be a fundamental system in future networks.

How Much Do You Know About WDM Technology?

WDM stands for Wavelength Division Multiplexing. It is a technology which combines two or more kinds of optical signals at different wavelengths and transmits them on one optical fiber. It is well known that white light consists of multiple colors of light, so a beam of white light passing through a prism creates a rainbow. WDM technology is much like this. It separates light with all the colors in the spectrum and transmits them on one optical fiber. Light at different wavelengths carries different signals and does not interfere with each other during the transmission. The following figure may help to learn about WDM.


Two Types of WDM


CWDM stands for Coarse Wavelength Division Multiplexing. It is a special technology defined by the ITU (International Telecommunication Union) in ITU-T G.694.2 spectral grids. It uses the wavelengths from 1270 nm to 1610 nm with a channel spacing of 20 nm. CWDM is suitable for use in metropolitan applications and cable television networks.


DWDM stands for Dense Wavelength Division Multiplexing. It is also a special technology defined by the ITU in ITU-T G.694.1 frequency grid. DWDM has a reference frequency fixed at 193.10 THz, with channel spacing varied from 12.5 GHz to 200 GHz, and a channel spacing of 100 GHz is common. In practical application, DWDM frequency is usually converted to wavelength. DWDM can transmit at most 80 channels (wavelengths) in the Conventional band (C-band) spectrum, and all 80 channels can transmit at the wavelength of 1550 nm at the same time.

There is a figure showing the comparison between CWDM and DWDM.


Fiber Optic Transmission in WDM System

Single Fiber Bidirectional Transmission

Single fiber bidirectional transmission refers to bidirectional communication on one strand of fiber. It utilizes two sets of same wavelengths for bidirectional transmission on one optical fiber. In single fiber bidirectional transmission system, each channel can realize bidirectional transmission.

Dual Fiber One-direction Transmission

Dual fiber refers to communication on two fiber. One fiber is used for communication on transmitted direction, and the other fiber is used for communication on received direction. In dual fiber one-direction transmission system, the same wavelength is usually used for both transmitted direction and received direction. In redundant system, the second fiber can be used as a backup fiber or it can provide an optical path in the opposite direction.


Upstream & Downstream

The transmission direction of signals can be expressed in upstream or downstream. The upstream direction refers to that the communication is sent from the service user to the service supplier, while the downstream direction is in the opposite direction.

The Topology Used in WDM system

Network Topology

By using multiple channels on optical fiber, the products of WDM bring higher efficiency to fiber optical network. An entire network usually consists of several different kinds of sub-network topologies. The network is invisible, but it can be identified by fiber cabling or topology. Sometimes, particular WDM products will be used in some networks with topology, such as Mesh, Ring, P2P (Point-to-Point), and P2MP (Point-to-Multipoint). Therefore, it is necessary to know about the type of network when choosing WDM product.

Ring Topology

In metropolitan area networks, the infrastructures are usually structured with ring topology. The network with ring topology is a closed loop consisting of a series of optical fiber spans. And those spans are terminated at the nodes in the loop. Each node is merely connected with two adjacent nodes through the optical fiber span. Ring network usually adopts dual fiber bidirectional system.



In network topology, node is the termination of single branch or multiple branches of the network. WDM network is composed of a set of nodes which are connected through optical fiber (physical topology). After establishing the light link between the nodes, a logical topology cover the entire network. Using WDM technology in optical fiber can make one node become several serving area which can expand the customer base and available bandwidth.


WDM Technology brings unprecedented increasing of bandwidth capacity and it becomes an ideal solution for more bandwidth and lower cost in modern telecommunication network. Therefore, some basic terminologies above are useful.

Introduction to Fiber Breakout Cable

Fiber breakout cable is a kind of fiber optic cable that contains several single-core optic fibers inside one outer cable jacket, and those single-core optic fiber are also covered by jackets. The design of fiber breakout cable adds strength for ruggedized drops, but the cable is larger and more expensive. Fiber breakout cable is suitable for short riser and plenum applications and also for use in conduits, where a very simple cable run is planned to avoid the use of any splicebox or spliced fiber pigtails.

Structure of Fiber Breakout Cable

The structure of fiber breakout cable (shown as the following figure) ensures a long life of the cable. The fiber breakout cable is composed of outer jacket, threaded connection device, breakout fiber assembly (tight-buffered fiber surrounded by aramid yarns outer layer and jacket ), reinforcing component and ripcord. In order to handle more easily, there is a 900 um coating which is easy to be stripped in the cable. Both the PVC and plenum cables are rated for fire safety.

fiber breakout cable

Features of Fiber Breakout Cable
  • A fiber breakout cable can “break out”several fibers at any length. Therefore, in is necessary to code fiber breakout cable for easy identification.
  • Each fiber has its own jacket and aramid reinforced component. This makes fiber breakout cable convenient to use and each fiber is very strong and durable. The following figure shows different types of fiber breakout cable.

fibre breakout cable

  • Each fiber adopts tight buffer technology or semi-tight buffer technology, so fiber breakout cable has a good ability to resist stripping.
  • Each fiber of fiber breakout cable is reinforced individually. Therefore, fiber breakout cable can be divided into several individual fiber optic lines. In this way, it takes less time to connect the termination and there is no need for the patch panel.
  • Due to the use of Kevlar component with increased strength, fiber breakout cable is much heavier and larger than the telecommunication type of cable with same fiber count.
  • Fiber breakout cable is better than standard fiber optic patch cable, because it eliminates the need of a fiber optic ducting system. The cable is particularly effective when equipment stands in a large area, for example, several floors in a huge building.
  • Fiber breakout cable has a better economy. It can save a lot of labor when connected to the termination. Although a cable that has more fibers is more than what you actually need, it is a good option in case of damage during the connection to the termination or future expansion.

Fiber breakout cable has a wide range of applications. It is suitable for short network design, such as LANs, data communication, video system and technology control environment. And fiber breakout cable is typically used in indoor applications: between the fiber optical distribution frame and the electronic equipment rack; between two electronic equipment racks. Some building environments require flame-retardant, non-toxic and smoke-free or flame-retardant with smoke and most fiber breakout cable can satisfy these requirements. And the cable is also suitable for pre-terminated cable assemblies. With a variety of designs and types, fiber breakout cable can meet the topological requirements in the hash environment. Fiber counts vary from single-core to 256. For installation which requires high strength, high reliability, maximum mechanical and environmental protection, fiber breakout cable is an ideal option.


Fiber breakout cable has good future prospects. With the trend of high-density in network communication, fiber breakout cable will play a more and more important role in network construction.

Introduction to Fiber Optic Pigtail

Fiber optic pigtail is a fiber optic cable that has an optical connector on one end and a length of exposed fiber on the other end. The connector side is used to link the equipment, while the other side is melted together with fiber optic cable. A fiber pigtail is single, short, usually tight-buffered. Technology of optical fiber fusion splicer is used during the process which can lower the insertion loss, that is, the end of the pigtail is stripped and fusion spliced to a single fiber of a multi-fiber trunk. Splicing of pigtails to each fiber in the trunk “break out” the multi-fiber cable into its component fibers for connection to the end equipment.

Fiber optic pigtail can have female or male connectors. Although single-fiber solution exists, female connectors could be mounted in a patch panel, often in pairs. In this way, they can be connected to endpoints or other fiber runs with patch fibers. In addition, male connectors can be used to plug directly into an optical transceiver.

Types of Fiber Optic Pigtails

As one type of fiber optic patch cable, fiber optic pigtail can be classified by different types of cables and connectors.

Fiber Optic Pigtails with Different Cable Types

Single-mode fiber optic pigtail is yellow. It transmits the optical signal with two types of wavelength, 1310nm and 1550nm. Accordingly, the transmission distance of single-mode fiber optic pigtail is 10km and 40km.

Multimode fiber optic pigtail is orange. It transmits the optical signal with the wavelength of 850nm. The transmission distance of multimode fiber optical pigtail is 5km and it is suitable for short distance transmission.

Simplex fiber optic pigtail is applied in one-way data transmission because the data is transmitted almost in one direction.

Duplex fiber optic pigtail can separately transmit and receive signals on two opposite directions at the same time.

Fiber Optic Pigtails with Different Connector Types

Here are illustration samples of the common ST/SC/LC/FC pigtails.

illustration sample

Some Other Types of Fiber Optic Pigtails

Bunch fiber optic pigtail adopts tight-buffered fibers with the cladding and cable jacket, widely used in transmission lines ans dense connection between the terminal equipment.

bunch pigtail

Ribbon fiber optic pigtail is characterize by its higher density of fiber. This is very important for the upstream applications which require high-density fiber cable.

ribbon pigtail

Waterproof fiber optic pigtail is produced strictly according to IEC standards. It is characterized by low insertion loss, high return loss, good interchangeability and repeat push-pull performance and it’s easy to use. Waterproof pigtail is equipped with strong jacket and waterproof sealed head connector which can be used in harsh environment.

waterproof pigtail


With the development of optical telecommunication network, a variety of optical fibers are widely applied in different occasion. And fiber optic pigtail is a great option for CATV, LANs, Gigabit data network testing, and some other fields.

Introduction to Fiber Optic Converter

Fiber optic converter is a media conversion unit of Ethernet transmission that exchange short-distance twisted-pair electrical signals with long-distance optical signals. The function of fiber optic converter is to convert optical signals into electric signals, and send it out, at the same time, convert optical signals received into electric signals and input to the receiver.

Fiber optic converter is typically used in real-world environments where the Ethernet cable can not cover and fiber must be used to extend the transmission distance. At the same time, it also play an important role in connecting the last mile of the fiber to the metropolitan area network and outer network. Fiber optic converter is also an inexpensive solution for the system which needs to upgrade from copper to fiber and for the user who lacks funds, manpower or time.

Characteristics of Fiber Optic Converter

Fiber optic converter typically has some basic characteristics:

  • Providing ultra-low latency data transmission.
  • Completely transparent to network protocols.
  • Using special ASIC chip to realize data-line forwarding. Programmable ASIC gathers multiple function on a single chip, offering the advantages of simple design, high reliability and low power consumption, resulting in higher performance and lower cost.
  • Rack-type devices can provide hot-swapping function for easy maintenance and uninterrupted upgrade.
  • The network management equipment can provide network diagnostics, upgrade, status report, abnormality report, control and can provide a complete operation and alarm log.
  • The device uses one plus one power supply design which supports ultra-wide power supply voltage to realize power protection and automatic switching.
  • Supporting ultra-wide operating temperature range.
  • Supporting a complete transmission distance (0-120 km).
Types of Fiber Optic Converters

Nowadays, a wide range of fiber optic converters are on the market, but in general, there are two types. One is applied in the connection network of copper and fiber optic cables, the other is applied in connection network of fiber optic cables. These two types of fiber optic converters can be divided into different subcategories. The following part will focus on the type of Ethernet optic converter.

Ethernet fiber optic converter is a kind of bidirectional transparent converter which provides Ethernet data signals to fiber data signals. It can transmit Ethernet signals along the fiber optic line and break the transmission distance limit of one hundred meters, allowing Ethernet network coverage to be great extended. Fiber optic data communication has been widely used in various fields because it has long communication distance, large capacity of data communication and is not easy to be disturbed. The original network systems were based on cable communication, but fiber optic converter can ensure the smooth conversion between electric signals and fiber optic signals. It is suitable for Ethernet network environment where high-speed, high data transfer, high performance and high reliability are needed, such as telecommunication, broadcasting, broadband network and so on.

In general, Ethernet fiber optic converter can be divided into three types. They are standalone media converter, industrial media converter and chassis-based media converter.

Standalone Media Converter

The standalone media converter is suitable for single user. Compared with other Ethernet fiber optic converter, standalone media converter is characterized with small size, low price, so it can greatly save space and cost. The structure of standalone media converter is compact and it is often deployed in racks, distribution boxes and other places where space is limited. Its plug-and-play packaging allows users to install and use quickly.

Standalone Media Converter

Industrial Media Converter

The industrial media converter is often used in harsh environment, such as high-speed tunnels, subways, sewage treatment, steel factory and so on. It can adapt to low temperature and high temperature. It has strong anti-lightning ability and anti-vibration ability.

Chassis-based Media Converter

Chassis-based Media Converter is a kind of fiber optic converter in the form of chassis structure. The power supply can achieve double automatic backup uninterrupted work and the system has over-temperature, over-voltage and over-current protection device. The internal adopts voltage compensation technology that fiber optic converter module can obtain reliable, accurate voltage supply. Chassis-based media converter is suitable for multi-user application. At present, many domestic chassis are sixteen-slot type products, that is, a chassis can be inserted up to sixteen fiber optic converter modules and each fiber optic converter module can operate independently or cooperate with each other in the rack.

Chassis Media Converter


As a kind of photoelectric conversion device, the Ethernet fiber optic converter can convert electrical signals into optic signals and transmit them in single-mode or multimode fiber optic cable, breaking the cable transmission limit of short distance and making use of fiber media to achieve a few or even hundreds of kilometers of long-distance transmission with high-bandwidth.

Introduction to Fiber Optic Patch Cable

Fiber optic patch cable is a fiber optic cable terminated with fiber optic connectors on both ends. It has thick layer of protection and is commonly used to connect the optical transmitter, receiver, and the terminal box in fiber optic network. Fiber optic patch cable is also known as fiber optic patch cord, fiber optic jumper.

The fiber optic patch cable is constructed from the core, the cladding, the coating, strengthening fibers and the cable jacket. Transparency of the core permits transmission of optic signals with little loss over great distances; the cladding causes light to be confined to the core of the fiber; the coating’s low refractive index reflects light back into the core, minimizing signal loss; the protective cable jacket minimizes physical damage to the core and coating. And on both end, there are connectors. (shown in the following figure.) For multi-core cable, the core measures 50 um to 65 um in diameter, approximately the thickness of a human hair; while the core of single-core cable is 8 um to 10 um in diameter.

Fiber optic patch cable

Fiber optic patch cable is characterized by:

  • Low insertion loss
  • High return loss
  • Good repeatability
  • Good interchange
  • Excellent environmental adaptability.

There are various types of fiber optic patch cables and they can be classified mainly by the types of cables and connectors.

Fiber Optic Patch Cables with Different Cable Types

Single-mode fiber is generally yellow with a blue connector, and it has a longer transmission distance.

Multimode fiber is generally orange or grey with a cream or black connector, and it has a shorter transmission distance.

Armored fiber optic patch cable uses a layer to protect the fiber inside from being bitten or other damage.

Bend insensitive fiber optic patch cable is widely used in FTTH and it is not sensitive to stress and bending.

Mode conditioning patch cable is a kind of double multimode patch cable and has a small length of single-mode fiber at the beginning of transmission length.

Fiber Optic Patch Cables with Different Connector Types

Fiber optic patch cable can be terminated with various types of connectors, such as LC, SC, ST, FC, MTRJ, E2000, MU and MPO/MTP. In addition, the connectors on both end can be the same or different. Therefore, the following part will focus on different types of connectors.

LC Connector

LC connector has a push and latch structure, with plastic shell and accurate 1.25mm ceramic ferrule. LC connector is in small size and has good performance. It is very popular and widely used for dense installation.

LC connector

SC Connector

SC stands for Subscriber Connector or Square Connector or Standard Connector. It is a kind of push and pull connector. SC connector has a locking tab which can make accurate alignment through ceramic ferrule. It features low cost, simplicity as well as good durability and it’s commonly used in data communication and telecommunication fiber optic market.

SC connectoe

ST Connector

ST stands for Straight-Tip and ST fiber optic cable has a bayonet rotary locking mechanism. There is a 2.5mm diameter ferrule on ST connector, the same as SC connector’s.

ST connectoe

FC Connector

FC connector is a kind of bolt type connector. FC stands for Fixed Connector which has a metal shell and bolt connection structure. The ferrule and sleeve on FC connector are the same with SC connector’s.

FC connector

MT-RJ Connector

MT-RJ connector which is developed from MT and RJ connectors. MT-RJ stands for Mechanical Transfer Registered Jack. There are plastic cover and ferrule on MT-RJ connector and it is characterized by the connection with two fibers, that is, two fibers are connected in one MT-RJ connector. MT-RJ connector has female type and male type. The difference between these two types is that the male type is constructed with two ferrules on one connector.

MT-RJ connector

E2000 Connector

E2000 connector has a spring-compressed valve and push-pull locking device to protect ferule from dust and wear. When inserting the connector, push-pull locking device will fully lock; when pulling it out, the spring-compressed valve will close automatically.

E2000 connector

MU Connector

MU connector has a plastic shell and push-pull locking mechanism. MU connector is small in size and has a ferrule with 1.25mm diameter. And MU connector is used in advanced optical transmission and exchange, user system or high speed data application.

MU connector

MPO/MTP Connector

MPO connector is high-density fiber optic connector and uses precise modeled MT ferrule. In single MPO patch cable, there are several fiber counts, such as 12 fibers, 24 fibers and 36 fibers. MTP is the optimized version of MPO. MTP adopts push-pull locking mechanism and it’s easy to insert and pull out.

MTP connector

Fiber optic patch cables are widely used in various fields, such as the connections to CATV (Cable Television), telecommunication networks, computer fiber networks and fiber test equipment. Applications include communication rooms, FTTH (Fiber to The Home), LAN (Local Area Network), FOS (fiber optic sensor), Fiber Optic Communication System, Optical fiber connected and transmitted equipment, Defense combat readiness, etc.