Multimode Fiber Optic Patch Cable Overview


We know that fiber optic patch cables play a very important role in the connection between devices and equipment. When talking about fiber optic patch cables, we usually divide them into multimode fiber optic patch cables and singlemode fiber optic patch cables according to the modes of the cable. What is multimode fiber optic patch cable? How many types of multimode patch cables are there? And what is the difference between multimode and singlemode patch cables? What are the applications of multimode patch cables? This text will solve those questions one by one.


Multi-mode fiber patch cables are described by the diameters of their core and cladding. There are two different core sizes of multi-mode fiber patch cords: 50 microns and 62.5 microns. Both 62.5 microns and 50 microns patch cable feature the same glass cladding diameter of 125 microns. Thus, a 62.5/125µm multi-mode fiber patch cable has a 62.5µm core and a 125µm diameter cladding; and a 50/125µm multi-mode fiber patch cable has a 50µm core and a 125µm diameter cladding. The larger core of multi-mode fiber patch cords gathers more light and allows more signals to be transmitted, as shown below. Transmission of many modes of light down a multi-mode fiber patch cable simultaneously causes signals to weaken over time and therefore travel short distance.

singlemode fiber vs multimode fiber

Types of Multimode Fiber Optic Patch Cable

Multimode fiber optic cables can be divided into OM1, OM2, OM3, and OM4 based on the types of multimode fiber. The letters “OM” stands for optical multimode. OM1 and OM2 belong to traditional multimode fiber patch cable, while OM3 and OM4 belong to the new generation fiber patch cable which provides sufficient bandwidth to support 10 Gigabit Ethernet up to 300 meters. The connector types include LC, FC, SC, ST, MU, E2000, MPO and so on. Different type of connector is available to different equipment and fiber optic cable.

By the materials of optic fiber cable jackets, multimode fiber patch cord can be divided into four different types, PVC, LSZH, plenum, and armored multimode patch cable. PVC is non-flame retardant, while the LSZH is flame retardant and low smoke zero halogen. Plenum is compartment or chamber to which one or more air ducts are connected and forms part of the air distribution system. Because plenum cables are routed through air circulation spaces, which contain very few fire barriers, they need to be coated in flame-retardant, low smoke materials. Armored fiber patch cable use rugged shell with aluminum armor and kevlar inside the jacket, and it is 10 times stronger than regular fiber patch cable.

Difference Between Singlemode and Multimode Patch Cables

Multimode and singlemode fiber optic patch cables are different mainly because they have different sizes of cores, which carry light to transmit data. Singlemode fiber optic patch cables have a core of 8 to 10 microns. Multimode fiber patch cable allows multiple beams of light passing through, while singlemode fiber cable allows a single beam of light passing through. As modal dispersion happens in multimode fiber cable, the transmission distance is relevantly nearer than singlemode fiber cables. Therefore, multimode fiber optic patch cable is generally used in relevantly recent regions network connections, while the singlemode fiber cable is often used in broader regions.

Applications of Multimode Fiber Optic Patch Cable

Multi-mode fiber patch cables are used to connect high speed and legacy networks like Gigabit Ethernet, Fast Ethernet and Ethernet. OM1 and OM2 cables are commonly used in premises applications supporting Ethernet rates of 10Mbps to 1Gbps, which are not suitable though for today’s higher-speed networks. OM3 and OM4 are best multimode options of today. For prevailing 10Gbps transmission speeds, OM3 is generally suitable for distance up to 300 meters, and OM4 is suitable for distance up to 550 meters.


Fiber optic patch cords are designed to interconnect or cross connect fiber networks within structured cabling systems. Typical fiber connector interfaces are SC, ST, and LC in either multimode or singlemode applications. Whether to choose a singlemode or multimode fiber patch cable, it all depends on applications that you need, transmission distance to be covered as well as the overall budget allowed.

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Select Best Ethernet Cable (Cat5/5e/6/6a) for Your Network

There is no doubt that wire connections that based on Ethernet cables usually have faster speed yet lower latency than Wi-Fi connections. And owing to the advanced technology, modern Ethernet cable can communicate at even faster speeds. When to install a network for your home, office or business, you may come across these questions: With various types of network cables available, what do I really need? Is it a Cat5, 5e, 6 or 6a, shielded or unshielded, UTP or STP? Thus, we are supposed to answer these frequently asked questions in the article.

Ethernet Cables Overview

Based on different specifications, Ethernet cables are standardized into sequentially numbered categories (“cat”) like Cat4, Cat5, Cat6 and etc. Each cable with a higher number is a newer standard, and these cables are backwards compatible. Sometimes the category can be further divided by clarification or testing standards, such as Cat5e and Cat6a. According to these different categories, it is easier for us to know what type of cable we need for a specific application.

Cat5e, Cat6, Cat6a cables

Cat5 (Category 5) cable serves as an older type of Ethernet network cable. It is designed to support theoretical speeds of 10 Mbps and 100 Mbps. Cat5 cable is capable of operating at gigabit speeds as well, especially when the cable is shorter, however, this cannot be guaranteed. Currently, Cat5 cable is rarely seen in the store, but there are still some with an older router, switch, or other networking device.

Cat5e (Category 5 enhanced cabling) cable is known as an improved version of Cat5 cabling. And with the enhanced signal carrying capacity, it is faster than Cat5 cable. Cat5e was made to support Ethernet, Fast Ethernet, and Gigabit Ethernet speeds over short distances and is backward compatible with Cat5. Meanwhile, it decreases the chance of crosstalk, the interference you sometimes inevitable to get between wires inside the cable. Cat5e cable also features improved durability because of improvements in the quality of the PVC protective jacket. It is more than suitable for most data cabling requirements.

Cat6 (Category 6) cable is the next step up from Cat5e. and it was specifically designed to consistently deliver 1 Gigabit Ethernet. When it comes to interference, Cat6 cable has even stricter specifications. Since the improvement in interference makes no big difference in regular usage, there is no need to rush out to Cat6 upgrade. However, when you propose to buy a new cable, you could try Cat6 because it is an improvement over the former types.

Cat6a (Cat6 augmented) is designed to 10 Gigabit speeds and is backward compatible with all the existing standards. Besides, it can be used in industries utilizing high-performance computing platforms to support very high bandwidth-intensive applications. Server farms, storage area networks, data centers and riser backbones are common 10G/Cat6a applications.

Categories of Ethernet Cables Signal Carrying Capacity Typical Uses
Cat5 Ethernet and Fast Ethernet Home, Home Office, Small Office
Cat5e (enhanced) Ethernet, Fast Ethernet, and Gigabit Ethernet (short distance) Home, Small Office, Gaming Consoles, Computer Networks
Cat6 Ethernet, Fast Ethernet, and 1 Gigabit Ethernet (consistent) Large Networks, Data Centers, Offices, Cat6 Certified Networks
Cat6a (Augmented) Ethernet, Fast Ethernet, and 10 Gigabit Ethernet Large Data Centers, Large Offices, Server Farms, Future Proofing New Equipment
Factors to Consider When Choosing Ethernet Cables

Through the revolution of Ethernet cables, we know that each newer standard brings higher possible speeds and reduced crosstalk. But how those categories distinct from each other? When to use unshielded, shielded, stranded, or solid cable? The following three factors are necessary to consider.

Unshielded (UTP) vs. Shielded (STP)

All Ethernet cables are twisted thus the shielding is used to further protect the cable from interference. Network cable typically comes in two basic types: STP (Shielded Twisted Pair) and UTP (Unshielded Twisted Pair).

UTP: UTP cable is comprised of four pairs of carefully twisted pairs of copper wire, insulated with carefully chosen material to provide high bandwidth, low attenuation and crosstalk. UTP can easily be used for cables between your computer and the wall, and it is also the most common type of cabling used in desktop communications applications.

STP: As for STP cable, cable pairs (not individual wires) are shielded by a metallic substance, and then all four pairs are wrapped in yet another metallic protector. This is done in the purpose of preventing interference via the usage of three techniques known as shielding, cancellation and wire twisting. The problem is that STP is harder to install. You will use STP for areas with high interference and running cables outdoors or inside walls.

UTP vs STP cablesPVC Jacket vs. Plenum Rated

PVC: The most common kind of network cable is PVC. PVC is usually used as the covering for patch cables, and often for bulk cables. The problem is that PVC covered will releases toxic smoke when burning. In this case, most local fire codes prohibit PVC covered cable from being used in air handling spaces. But it is accepted to use PVC cable in wall installations. To be on the safe side, you should check your local fire codes.

Plenum: Plenum rated cable has a covering that burns without toxic smoke. In construction, plenum refers to the separate space provided for air circulation, heating, and venting. In a standard commercial building, the plenum is the space between the drop ceiling and the structural ceiling. While in residential installations, the plenum could be in a few places such as the floor when floor level air circulation is used.

PVC vs. Plenum

Stranded vs Solid Core

By solid and stranded Ethernet cables, it means the actual copper conductor in the pairs. The differences lie in that solid cable uses a single piece of copper for the electrical conductor, while stranded uses a series of copper cables twisted together. There are two main applications for each type you should know about.

Stranded vs. Solid Core

Stranded cable is more flexible and should be used at your desk, or anywhere you may move the cable around often. It is much better for patch cables where flexibility is very important.

Solid cable is not as flexible but it is also more durable, which makes it ideal for permanent installations as well as in walls and ceilings. Termination will be easier and more reliable with solid core cable. Besides, it has very good attenuation properties thus easier to send a signal over. As such, solid core is best for long runs.


As the core and backbone of any network, network cables matter to overall communication and efficiency. Cat5e can be used for most home and office applications, and Cat6 and Cat6a to establish a large network such as high speed servers and data centers. However, your final decision should be based on your need and network demand, and remember to take the above factors into consideration.

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How to Build a Passive DWDM Network?

DWDM technology has been regarded as an ideal solution for long haul optical transmissions. Usually the common passive system is CWDM but not DWDM. However, passive DWDM network also can offer perfect performance in some cases. This post focuses on the process of building a passive DWDM network, which includes the selection of related products, loss calculation and other factors needed to consider.

Passive DWDM Network Basis

In general, “passive” in DWDM optical networks means there are no powered parts inside, which is opposed to an active system that has a powered element like EDFA (erbium doped amplifier). In a passive DWDM network, the line functions only due to the use of optical transceiver. Passive DWDM systems have a high channel capacity and potential for expansion. The drawback is that passive DWDM networks only suit long runs applications.

passive DWDM

Passive systems have the same wavelength channel capacity as active systems. Though passive DWDM network has a limited transmission distance, it is more cost-saving and simpler compared with active DWDM systems. Because it doesn’t need active components like optical amplifiers or OEO transponder. And passive DWDM network is easy to control due to its physical cabling that the wavelength is tied to the optic.

How to Build a Passive DWDM Network?

Building a passive WDM network, no matter passive CWDM or DWDM network, is not an easy task. There are many factors that need to be taken into consideration. Now in the following part, I will give an example of a client to illustrate how to build a passive DWDM network.

Targeted Passive DWDM Network Overview & Design

Situation: there are four optical rings DWDM links using single mode fiber cable. The distance of each ring is 10km. And each ring has up to 21 outdoor cabinets.

Requirements: all equipment should be passive (no power/cooling required); all outdoor cabinets will serve business customers with direct fiber cable. (PON splitters 1:8 at least); the ring should be designed with redundancy standards. And the goal is to serve our customers with high quality protected data services via fiber optic cables.

Here is a simple graph showing the passive DWDM network structure (cabinets have been omitted in this graph).

DWDM network

Selection of products. According to the requirement of the customer, these products are needed in the connection.

Product Description
DWDM MUX/ DEMUX 32 Channels Single Fiber DWDM MUX/ DEMUX
DWDM OADM Single Fiber DWDM OADM, Splice Pigtailed ABS Module
DWDM SFP 1000BASE-DWDM SFP 100GHz 120km DOM Transceiver
Fiber optic patch cord 10m Duplex Fiber Optic Patch Cord

Loss calculation. Each connector introduces loss in optical connections. Considering the changes of some components, the loss calculation is a little different from the one I mentioned in the article How to Calculate DWDM System Loss in Long Haul Transmission, which just shows the calculation of part connections in a link. In this connection, the total loss=fiber optic mux loss+ fiber loss+connectors loss+ OADM loss. According to the components used, the total loss is 32dB.

Deployment. After determining the products and power budget of the whole links, the next step is to deploy all components in the links. And learning some tips like avoiding end face contamination, or not bending fiber cables, will be helpful.


This post just gives a simple illustration to build a passive DWDM network. In fact, in actual DWDM network, there are various factors to consider. For instance, transmission distance, data rate, power budget, selection of optical components, etc. And even in final deployment, other problems may also arise. Therefore, quality products and professional team are important when designing passive DWDM networks. FS.COM, as a professional optical components and solutions supplier, can provide you reliable support for your DWDM networks. Welcome to visit FS.COM for more detailed information.

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Effectively Manage Power Cord in Your Rack

Power cords are extensively adopted in data centers and server rooms to deliver power to various electronic loads and computer equipment. Judging solely from their appearance, you may find that there exist a confusing array of power cords with various plugs and receptacles. Not to mention that the application of each also varies largely. So how to identify power cords and get them organized within your IT rack? This article may solve your problem.

What to Know About Power Cord?

The connection of electronic equipment to the AC power supply is achieved by power cord, which has detachable connectors on both ends. There are three parts involved in a power cord: a cable plug (male connector) that can be inserted into AC outlet to provide power, a receptacle (female connector) to be attached to equipment, and a cord that connects these two parts. In this section, power cords with various connector types are presented, with a detailed analysis of their names, appearance and applications.

power cord

IEC 60320 Power Cord

The International Electrotechnical Commission (IEC) has published international standards IEC 60320 for power cords. You can find IEC 60320 C13 to C14 connector on almost all personal computers and monitors. It has a rating of 10 amps and the female connector end is noted as C13 while the male connector end is noted as C14. The IEC 60320 C19 to C20 connectors are rated for 16 amps and again have a female connector end (C19) and a male connector end (C20). C19 to C20 connectors are commonly used for devices such as some servers and UPS systems. The details of IEC C13 to C14 power cord and C19 to C20 power cord are presented below.

IEC 60320 C13-C14 & C19-C20

NEMA Power Cord

Established by the National Electrical Manufacturers Association (N.E.M.A.), NEMA describes various connectors used on power cords throughout North America and some other countries. NEMA devices range in amperages from 15-60, and in voltages from 125-600. The most common NEMA connectors are the 5-15 and 5-20 designations. The first number indicates the plug configuration. This includes the number of poles and wires and the voltage. The second number in the code indicates the amp rating of the device, and is followed by an “R” for receptacle, or a “P” for a plug. For example: 5-15R is a 125V, 2-pole, 3-wire receptacle rated at 15 amps and is the most commonly found power outlet in houses in the U.S.

NEMA 5-15p to 5-15r

Amps vs Wire Gauge

There is a direct correlation between cable length, amperage and wire gauges. The following list is a basic breakdown of the relationship of amperage vs wire gauge. These are only basic guidelines, so as the length of the cord is increased either the amps will decrease or the wire gauge will have to be increased.

Amperage Recommended Wire Gauge
7a 20 AWG
10a 18 AWG
13a 16 AWG
15a 14 AWG
20a 12 AWG
Wire Color-Coding

For safety and convenience reasons, wire color-coding standards were developed for the jackets of the individual conductors inside power cords. Below is a list of the US and European color-coding standards. Please note that these apply to most power cords in the US and Europe. Color-coding may vary in certain applications.

Wire USA Color EU Wire Color
Live Wire Black Brown
Negative Wire White Blue
Ground Wire Green Yellow/Green

Safety Issues: connectors of power cords are made differently for various utilization voltages, with the purpose of preventing equipment designed for one voltage to be inadvertently connected to another. Using power cords with either higher or lower voltage than the equipment designed voltage is harmful-it may damage the equipment or present a fire hazard.

Tips for Manage Power Cords Within Racks

Power cords and data cords, such as fiber optic cables or copper cables, are inevitably co-exist within an IT rack. It is necessary to get them organized for better network performance and aesthetic appeals. We offer three tips here to achieve efficient power cord management.

Tip One: Separate power and data cables

We know the fact that EMI can deteriorate the performance of cables. Separating power and fiber optic cables contributes to minimize the effects of EMI, prevent erratic or error-prone data transfer and reduce human error. It you must cross power and data cables in some specific environments, try to cross them perpendicular to each other to minimize EMI. It is suggested to bundle data cables on one rear side of the IT rack and distribute power cables at the other rear side of the IT rack. Use high quality fiber optic cables is also beneficial to minimize EMI.

separate power cord and data cord

Tip Two: Use colored power cords

Good identification and administration of power cord are essential. Using colored power cords is a good practice to simplify the management of equipment inside the rack. Colored power cord allows for easy identification of power paths, simplified manageability of main and redundant power sources and efficient installation, giving your server room a clean and organized appearance.

colored power cord

Tip Three: Label power cords

Labeling both ends of the power cord is an integral part of the infrastructure installation and testing process, and is simply a good investment. It will save you much time and energy when finding the target power cord, and distinguishing one from another.


Power cord serves as an integrate part to provide the necessary power supply to your network. In this article, we have guide you through the basic knowledge associated with power cords, as well as some tips for efficient power cord management in IT racks. Hope it could help you to identify and choose the ideal power cord.

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How to Place EDFA for DWDM Distance Extension?

Erbium doped fiber amplifier (EDFA) is the latest state-of-the-art solution for amplifying optical signals in optical transmission systems. It has become a key enabling technology and the dominant amplification device deployed in optical networks. Together with DWDM technology, EDFA has made it possible to transmit data over long distance. Broadly speaking, optical amplifiers may be used within an optical network as boosters, in-line amplifiers and pre-amplifiers. This article guides you to optimize your DWDM network reach by setting EDFA amplifiers in proper position.

What Is EDFA and How Does it Work?

EDFA works to directly amplify any input optical signal, eliminating the need to convert the signal into the electrical domain, thus offering the potential to reduce bandwidth transport costs. Since fiber attenuation limits the reach of a non-amplified fiber span to approximately 200 km, wide area purely optical networks cannot exist without an optical amplifier. Currently, EDFA has gained in more popularity because of features such as polarization independent gain, low noise, low cost and very low coupling losses.

edfa basic configuration

The basic form of EDFA consists of a length of EDF, a pump laser, and a WDM system for combining the signal and pump wavelength so that they can propagate simultaneously through the EDF. The most common configuration of EDFA is the forward pumping configuration using 980nm pump energy. Which offers the best overall design with respect to performance and cost trade-offs.

Different Positions and Functions of EDFA in DWDM Links

Within a DWDM system, EDFA can be placed in three different places for power compensation: used as booster optical amplifiers on the transmitter side to provide high input power to the fiber span, as in-line amplifiers to compensate for fiber loss in the transmission, and as preamplifiers at the receiver end to boost signals to the necessary receiver levels.

edfa in DWDM network

A booster optical amplifier operates at the transmission side of the link, working to amplify aggregated optical input power for reach extension. Booster EDFA is designed to enhance the transmitted power level or to compensate for the losses of optical elements between the laser and optical fibers. It is usually adopted in a DWDM network where the multiplexer attenuates the signal channels. Booster optical amplifier features high input power, high output power, and medium optical gain.

booster optical amplifier

An in-line amplifier is generally set at intermediate points along the transmission link in a DWDM link to overcome fiber transmission and other distribution losses. Optical line amplifier is designed for optical amplification between two network nodes on the main optical link. In-line amplifiers are placed every 80-100 km to ensure that the optical signal level remains above the noise floor. It features medium to low input power, high output power, high optical gain, and a low noise figure.

optical line amplifier

A pre-amplifier operates at the receiving end of a DWDM link. Pre-amplifiers are used for optical amplification to compensate for losses in a demultiplexer located near the optical receiver. Placed before the receiver end of the DWDM link, pre-amplifier works to enhance the signal level before the photo detection takes place in an ultra-long haul system, hence improving the receive sensitivity. It features medium to low input power, medium output power, and medium gain.


How to Set up EDFA for DWDM Network Extension?

By placing booster optical amplifier, optical line amplifier and pre-amplifier in different position of a DWDM link, the possible network reach extension can be achieved.

Booster for 10 Gbps point-to-point connections up to 170 km

Distances of optical transmission systems can be extended by using EDFA. Three different EDFA types can be used depending on the required distance and existing locations. Simply by putting a booster optical amplifier at the beginning of a DWDM link, up to 170 km can be accomplished in a point-to-point connection.

Booster for 10 Gbps up to 170 km

Pre-amplifier ensures up to 250km reach without any in-line amplifier

As the booster amplifier set at the beginning extends the link reach to 170 km, with the additional use of a pre-amplifier at the end of a transmission, the achievable distance of the entire system can be increased up to 250 km.

Pre-amplifier ensures up to 250km reach

Single in-line amplifier for 400km transmission even With100 Gbps

Installing an EDFA at one repeater site, a distance of up to 400 km can be realized. And this can be further extended if more repeater sites are used to place optical line amplifier. All three types of amplifiers are already designed to support 100 Gbps bandwidth for realizing up to 1000 km in a point-to-point connection. For this purpose multiple repeater sites and a Forward-Error-Correction (FEC) integrated in the used optics are required.

Single in-line amplifier for 400km with100 Gbps


Appropriate deployment of EDFA as booster, in-line amplifier and pre-amplifier in a DWDM link contributes to optimize network performance for extending the reach. Which also increases data capacity required for current and future optical communication system. Hope the discussion in this article is informative enough to get a better understanding of EDFA optical amplifier.

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DWDM Topology Design: How to Make it Right?

Network expansion spurs the demand for faster data transmission and higher capacity over the network. In this case, DWDM emerges as a cost-effective solution to handle these issues, working efficiently to combine multiple wavelengths together and sent them over one single fiber. With the ability to carry up to 140 channels theoretically, higher capacity can be achieved by DWDM technology. This article guides you through some basics of DWDM topology.

Common DWDM Topology Overview

DWDM networks are grouped into four major topological configurations: DWDM point-to-point with or without add-drop multiplexing network, fully connected mesh network, star network, and DWDM ring network with OADM nodes and a hub. The requirements of each DWDM topology differ, and based on various application, it may involve different optical components. Besides these four common DWDM topology, there also exists hybrid network topology, consisting of stars and/or rings that are interconnected with point-to-point links.

Configurations of DWDM Topology

This section illustrates the four basic DWDM topology configurations, help to understand the major differences and applications of them.

Point-To-Point Topology

Point-to-point topology is typically found in long-haul transport, which demands for ultra high speed (10-40Gb/s), ultra high aggregate bandwidth, high signal integrity, great reliability, and fast path restoration capability. The transmitter and receiver within this DWDM topology can be several hundred kilometers away, and the number of amplifiers between the two end points is generally less than 10. Together with add-drop multiplexing, point-to-point DWDM topology enables the system to drop and add channels along its path. A DWDM point-to-point system includes lasers, an optical multiplexer and demultiplexer, fibers, optical amplifiers, and an optical add-drop multiplexer.

point-to-point dwdm topology

Ring-Configuration Mesh and Star Networks

Basically, a DWDM ring network includes a fiber in a ring configuration that fully interconnects nodes. Two fiber rings are even presented in some systems for network protection. This ring DWDM topology is commonly adopted in a local or a metropolitan area which can span a few tens of kilometers. Many wavelength channels and nodes may be involved in DWDM ring system. One of the nodes in the ring is a hub station where all wavelengths are sourced, terminated, and managed, connectivity with other networks takes place at this hub station. Each node and the hub have optical add-drop multiplexers (OADM) to drop off and add one or more designated wavelength channels. As the number of OADMs increases, signal loss occurs and optical amplifier is needed here.

dwdm ring network

In the ring DWDM topology, a hub station works to manage channel assignment so that a fully connected network of nodes with OADM is accomplished. The hub also makes it possible to connect other networks. A DWDM mux/demux can be connected to an OADM node to multiplex several data sources. The following picture demonstrates a simple DWDM ring topology with a hub and two nodes (A and B).

dwdm ring topology with hub

Transmit and Receive Directions of DWDM Hub

In the previous part, we’ve mentioned DWDM hub, which serves as a very essential parts in a DWDM system. Here we further explain the transmit and receive direction of a DWDM hub, proving system solutions for your reference.

Transmit Direction

A DWDM hub accepts various electrical payloads, such as communications transport protoco/Internet Protocol (TCP/IP), asynchronous transfer mode (ATM), STM, and high-speed Ethernet (l Gb/s, 10 Gb/s). Each traffic type (channel) is sent to its corresponding physical interface, where a wavelength is assigned and is modulated at the electrical-to-optical converter. The optically modulated signals from each source are then optically multiplexed and launched into the fiber.

dwdm hub in the transmit direction

Receive Direction

When a hub receives a WDM signal, it optically demultiplexes it to its component wavelengths (channels) and converts each optically modulated signal to a digital electrical signal. Each digital signal then is routed to its corresponding electrical interface: TCPIIP, ATM, STM, and so on However, that each channel requires its own clock recovery circuitry because all channels may be at different bit rates.

dwdm hub in the receive direction


The network topology of your DWDM system depends on various factors, including the number of nodes, maximum traffic capacity, scalability, number of fiber links between nodes and so on. Attentions also should be attached to the network components involved in the DWDM system. Hope this article could help to get more understanding towards DWDM technology.

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IP/WDM vs. IP/OTN: Which One to Choose?

The unceasingly demand for Internet-based services makes carrier IP networks a more critical social infrastructure. Operators are required to offer higher speeds, larger capacities and higher reliability network. There emerge two solutions to tackle this issue: IP/WDM and IP/OTN. IP/WDM consists of core routers connected directly over point-to-point WDM links, whereas IP/OTN connects the core routers through a reconfigurable optical backbone (OTN) consisting of electro-optical cross-connects (OXCs) interconnected in a mesh WDM network. This article guides you to choose between them.

Basics of WDM Technology

WDM technology is nothing new for us since it is rather prevalent especially for long haul data transmission. Its ability to provide potentially unlimited transmission capacity remains to be the most featured benefits. Either by simply upgrading the equipment or by increasing the number of lambdas on the fiber, network capacity can be obtained. It is the best choice for applications where channel density/bandwidth is of high priority. Aside from the bandwidth advantage, it also possesses these compelling merits.

wdm technology

  • Transparency—Being a physical layer architecture, WDM can transparently support both TDM and data formats such as ATM, Gigabit Ethernet, ESCON, and Fibre Channel with open interfaces over a common physical layer.
  • Scalability—WDM can leverage the abundance of dark fiber in many metropolitan area and enterprise networks to quickly meet demand for capacity on point-to-point links and on spans of existing SONET/SDH rings.
  • Dynamic provisioning—Fast, simple, and dynamic provisioning of network connections enable high-bandwidth services in days rather than months.
OTN Network Explanation

ITU-T defines OTN as a set of optical network elements (ONE) connected by optical fiber links, being able to provide functionality of transporting, multiplexing, switching, management, supervision and serviceability of optical channels carrying client signals. OTN was designed to optimize existing resources of a transport network. It is a digital wrapper that provides an efficient and globally accepted way to multiplex different services onto optical light paths. The advantages of OTN consist of the following aspects.

OTN network

  • It has the facility to work with DWDM and SDH equipment within banded or mesh networks.
  • Transmits SDH services, without termination of the signal at each network element, the signal transport is transparent including the clock and byte header.
  • Easily combine multiple networks and services on a common infrastructure entirely in the optical domain and transparent to the format and the speed of the signal carrying client, allowing you to create a multi-platform client.
  • The OTN services offering is gully software programmable via a single line card, so that the protocols, connectivity and functionality can be reprogrammed remotely as they change services or customers.
IP/WDM vs. IP/OTN: How to Choose From?

Before we go any further, let’s first look at the basic architecture of each. In the IP/WDM architecture, core routers are connected directly over point-to-point WDM links, whereas in the IP/OTN architecture, they are connected through a reconfigurable optical backbone (OTN) consisting of electro-optical cross-connects (OXCs) interconnected in a mesh WDM network. (See the figure below). We assume that each Point of Presence (PoP) or CO (Central Office) consists of four IP routers. It is clear that in IP/WDM, the routers are connected directly to the WDM systems, which connect them to neighboring PoPs. On the other hand, in IP/OTN, there is an intermediate element (OXC) which is responsible for connecting IP routers from different PoPs.

IP over WDM vs. IP over OTN

The major differences of these two approaches include the following aspects:

1. In IP/WDM, traditional transport functions such as switching, grooming, configuration and restoration are eliminated from the SONET/SDH layer and moved to the IP layer which is supposed to be enhanced by MPLS. Alternatively, the optical layer is the one that deals with the aforementioned, exploiting the intelligence of OXCs.

2. IP/OTN solution is more scalable than IP/WDM since the core of the network is based on the more scalable OXCs rather than IP routers.

3. IP/OTN is more flexible to traffic changes than IP/WDM.

4. IP/OTN, the optical transport layer provides the restoration services in a fast and scalable way (optical shared mesh restoration), whereas in IP/WDM restoration is achieved by IP rerouting which is a slow process and may lead to instability in the network.

5. When comparing the cost, IP/WDM appears to be a more cost-prohibitive solution than the IP/OTN architecture. Furthermore, as years go by and total traffic increases, the cost difference between both architectures is more severe.


From what we presented in the article, it is clear that IP/OTN is a more cost-efficient solution. And the savings increase rapidly with the number of nodes and traffic demands between them. Furthermore, IP/OTN is superior over IP/WDM in other qualitative terms like scalability, availability and resiliency. FS.COM endeavors to provide cost-effective and feasible optical network solutions. For more information, please visit

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CWDM Network: Technology Overview and Common Applications

Fiber exhaust is an inevitable problem constantly faced by carriers since the demand for higher speed bandwidth never ceases. The ever-improving wavelength division multiplexing (WDM) technology nowadays is increasingly used to boost network capacity, enabling carriers to deliver more services over their existing fiber infrastructure. CWDM, as one form of the mature WDM technologies, is a perfect fit for access networks and metro/regional networks. This article addresses the CWDM fundamentals and its common applications, and how CWDM helps to maximize network capacity effectively.

CWDM Technology at a Glance

Coarse wavelength division multiplexing (CWDM) came into prominence as a cost-effective alternative to maximize network capacity in the access, metro and regional network segments. It gains in more popularity in area with a relatively moderate traffic growth due to its simple deployment and low cost. ITU-T G.694.2 defines 18 wavelengths for CWDM transport ranging from 1270 to 1610 nm, spaced at 20 nm apart. But 8 wavelength in the 1470-1610nm band is mostly used since there exist high attenuation in the 1270-1450 nm band. This technology shines out in access network deployments by obtaining the advantages of flexible add-drop capacity and network design simplicity.

CWDM wavelength

Common Applications of CWDM

After going through the basics of CWDM technology, this section will further explain its common applications. CWDM is primarily deployed in two areas: metropolitan and access networks. Let’s see how they could benefit from applying it.

Fiber Exhaust Relief

Fiber exhaust appears to be a severe problem that carriers endeavor to solve, especially for some metropolitan networks where data traffic increases continuously. Adding CWDM to the original optical network presents a cost-efficient and simple approach to this problem. In this case, carriers can add new services over a existing single optical fiber, while not interrupting service for existing customers. This solution is ideally suited for carriers that desires to increase the already installed network capacity without new fiber construction.

CWDM increases capacity

Enterprise LAN and SAN Connection

When interconnecting geographically dispersed Local Area Networks (LANs) and Storage Area Networks (SANs), CWDM rings and point-to-point links offer an optimum option. It is beneficial to integrate multiple Gigabit Ethernet, 10 Gigabit Ethernet and Fiber Channel links over a single fiber for CWDM point-to-point applications or for ring applications.

CWDM ring

Adoption in Metro Networks With Lower Cost

4 channel CWDM system offers an ideal solution for smaller metro/regional markets which demand for moderate traffic growth. This configuration can expand the available capacity four times over an existing network, enabling less deployment cost than the commonly adopted 8 channel system. Meanwhile, the scalability of this 4 channel system also allows carriers to upgrade to 8 channel systems when the need occurs.

Central Office to Customer Premise Interconnection

Coarse WDM system is also well-fitted for metro-access applications such as Fiber to the Building (FTTB). Let’s take the most widely used 8 channel CWDM network for example, it is capable of delivering 8 independent wavelength services from the Central Office (CO) to multiple business offices located in the same building.

CWDM for FTTH application

Combining With PON

Passive Optical Network (PON) is a point-to-multipoint optical network to deliver bandwidth to the last mile. It is cost-effective because it uses passive devices (splitters for example) instead of expensive active electronics. The issue exists in PON is that the amount of bandwidth they can support is rather limited. Since CWDM serves to multiple bandwidth, when combining it with PON, each additional lambda becomes a virtual point-to-point connection from a central office to an end user. If one end user in the original PON deployment needs his own fiber, adding CWDM to the PON fiber creates a virtual fiber for that user. Once the traffic is switched to the assigned lambda, the bandwidth taken from the PON is now available for other end users, so the access system can maximize fiber efficiency.


CWDM has clearly become the preferred method for increasing the bandwidth of metro/regional and optical access networks quickly, simply and at lowest cost. And it has proven to be sufficiently robust and reliable for upgrading the optical network to accommodate future growth. Hope this article could help to get a better understanding of coarse WDM technology.

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Implementing Passive CWDM to Upgrade Access PONs

Coarse Wavelength Division Multiplexing (CWDM) has proven itself to be a preferred approach to elevate the bandwidth of optical access networks, offering quicker and simpler installation and lower overall cost. Passive CWDM, which requires no electrical power at all, is considered reliable and robust to deploy in the most demanding environment. It generally offers lower cost and more flexible installation and network expansion. This article demonstrates how to use passive CWDM technology to upgrade access PONs.

Why Passive CWDM for Access PONs?

Passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components. CWDM multiplexing components are compact enough to easily retrofit into existing fiber splice cassettes for installation into street cabinets or other forms of outside enclosure. Besides, it also processes the following merits:

  • Predictably low equipment and operating cost
  • Quick and efficient network upgrade
  • Simplicity of specification and simplicity of deployment
  • Sufficiently flexible solutions that facilitate expansion
  • Open standards, nothing proprietary
CWDM and Add/Drop With Access PONs

For PON networks, be it in the ring or point-to-point structures, not all capacity is needed at a single optical node. Therefore, data transported over certain channels may be added/dropped from the fiber as required. And it may be implemented at any CWDM node at any location in the field. The picture below illustrates how to achieve this. This is generally cost effective and simple to perform. A passive CWDM upgrade simply eliminates the need for deployment of additional network equipment.

cwdm add drop with access pons

The advantages of the PON architecture above lies in the low CAPEX, low OPEX and no electrical power required. And that it can be quickly and inexpensively upgraded when additional bandwidth demands arise.

How to Upgrade Access PONs With Passive CWDM?

With the prevalence of FTTH networks, access networks between the central office (CO) and the subscribes must be upgraded to keep pace with the hunger bandwidth. The figure below shows a typical PON architecture, with an optical line terminal (OLT) located in the CO to transmit traffic to approximately 16 to 32 residential drop points, and PON splitters located at fiber distribution hubs between the OLTs and subscribers’ optical network terminals (ONTs), enabling one OLT port and laser transceiver to be shared across many drop points.

generic pon network using remote olts

Passive CWDM enables better fiber capacity utilization and supports far greater data traffic as the bandwidth demands from the ONTs increase. It permits network operators to implement many more optical nodes over multiple locations with minimal capital investment and virtually no additional operating cost. The following case presents how to use passive CWDM for access PONs upgrade.

Case: In this case, existing subscribers intend to upgrade to higher value-added bandwidth services. The 622 Mb/s downstream capacity between the CO and the OLT, appropriately 20 Mb/s to each subscriber is proven insufficient, which must to increase.

limited fiber capacity in pon

Solution: The adequate bandwidth requires a downstream CO/OLT link bandwidth of 2.5 Gb/s. Multiplying the number of bidirectional channels traveling between the CO and OLT by four demands four CWDM wavelengths. The upgraded passive CWDM based network (shown below) relives the fiber exhaust and boosts the bandwidth of the CO/OLT link. This installation requires four channel-specific (color coded) transceivers plugging into the router/switch, the associated patch cables, the rack-mounted CWDM module and the snap in passive CWDM cassette located in the OLT.

passive cwdm adds capacity in pon

Benefits: The passive CWDM upgrade can be accomplished within hours, while the cost concerning material, labor, equipment and training is far less than that of laying a new fiber cable. Which is both energy-saving and cost-efficient.

Using CWDM to Expand EPON Bandwidth

Passive CWDM is also beneficial to Ethernet PON (EPON). Let’s see how it works in EPON through the case below.

Case: The figure below shows a common EPON architecture, which serves up to 64 subscribers, all sharing a single 1.25Gbps bidirectional optical Ethernet feed line. The theoretical maximum sustainable data-rate for each is roughly 16 Mb/s. The 16Mb/S downstream capacity should be increased since higher bandwidth services become available.

epon deployment

Solution: A four channel passive CWDM extension effectively multiplies the downstream capacity without affecting the upstream traffic. A rack-mounted CWDM unit in the CO and a miniature hardened CWDM module deployed in the fiber distribution hub increases the revenue earning potential while minimizes OPEX and CAPEX.

passive cwdm in epon

Benefits: In this case, the four channel CWDM upgrade promotes the throughput of the downlink by a factor of four while demanding minimal modification of the existing infrastructure.


A passive CWDM method provides the unique advantages of low CAPEX, minimal OPEX and rather simple yet reliable upgrade planning and implementation. More importantly, passive CWDM also preserves scalability and network flexibility for future network expansion and bandwidth demand changes. Hope this article is informative enough for getting a better understanding towards passive CWDM.

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Hybrid CWDM-DWDM System Boosts Your Network Capacity

Should I choose a medium capacity but more cost-effective CWDM solution, or to adopt the cost-prohibitive DWDM approach with comparably enhanced capacity? This is a problem that consistently faced by WDM technology users. The wrong decision, however, may inevitably lead to bandwidth shortage or even potential bankruptcy derived from unnecessary capacity investment. This article introduces the hybrid CWDM-DWDM solution that combines both CWDM and DWDM technologies within a single system, helping decrease costs and simplify installation while maintain the flexibility to upgrade.

Hybrid CWDM-DWDM System Explanation

Hybrid CWDM-DWDM system utilizes the technology to merge DWDM and CWDM traffic seamlessly at the optical layer. Which allows carriers to add many channels to networks originally designed for the more limited CWDM capacity and reach. In other words, hybrid CWDM-DWDM system is used to empower CWDM system by integrating CWDM and DWDM equipment. Hybrid CWDM-DWDM system deliver true pay-as-you-grow capacity growth and investment protection. It offers a simple, plug-and-play option for creating hybrid system of DWDM channels interleaved with existing CWDM channel plans.

Benefits of Hybrid CWDM-DWDM System

Hybrid CWDM-DWDM system typically provides three benefits for carriers and users:

  • Reduced Cost: CWDM is more cost-effective than DWDM due to the lower cost of lasers and the filters used in CWDM modules. This cost saving becomes quite significant for large deployments.
  • Pay-As-You-Grow: Adding one new channels at a time allows for on-demand service introduction with minimal initial investment—a critical feature in terms of reduced OPEX and CAPEX spending.
  • Investment Protection: Carriers and end-users need always to bear the future growth in mind. With hybrid CWDM-DWDM system, carriers no longer have to choose between CWDM and DWDM—both options can be deployed simultaneously or as part of future growth. This module can be used in either CWDM or DWDM system. Current capital investment can always be used in the upgraded network.
How to Deploy Hybrid CWDM-DWDM System

The CWDM wavelength grid typically has 16 channels spacing at 20 nm intervals, with 8 channels (1470 nm-1610 nm) of them are most commonly used. Within the pass band of these channels, it is capable of adding 25 100 GHz spaced DWDM channels under the 1530nm envelope and 25 more under the 1550nm envelope. However, it is not so practical to add 25 DWDM channels in the pass-band of both the 1530nm and 1550nm CWDM channels. DWDM filter technology does allow 38 additional channels to clear the CWDM archway, which is shown as following.

hybrid CWDM-DWDM systems

To add more DWDM channels to the MUX side of the conventional CWDM system, one need to plug in a DWDM MUX with the appropriate channels under the pass band of the existing CWDM filters. The picture below illustrates the configuration of a CWDM system upgraded with 38 additional 100 GHz spaced DWDM channels. This hybrid CWDM-DWDM system consists of 38 DWDM channels and the existing 6 CWDM channels. The equipment required to go from the first architecture to the second are 2 DWDM MUX/DEMUXs, as well as the additional transmitter and receiver pairs. The additional loss incurred by the upgrade is equal to the additional loss of the DWDM elements and the additional connection points.


Flexible Hybrid CWDM-DWDM System Solution by FS.COM

The most vital elements concerning hybrid CWDM-DWDM system are the CWDM MUX/DEMUX and DWDM MUX/DEMUX. FS.COM developed and introduces FMU series products to facilitate installation and operation of WDM MUX/DEMUX. The prominent feature of this series products is that they combine the MUX/DEMUX into half-U plug-in modules, which can be installed in a 1U rack. As for hybrid CWDM-DWDM system, a FMU CWDM MUX/DEMUX and a DWDM half-U plug-in module can be installed together in a FMU 1U rack chassis, facilitating connections of these two modules while allowing for better cable management and network operation in hybrid CWDM-DWDM system.



Hybrid CWDM-DWDM system generally offers a cost-effective and future-proofing approach for service providers and end-users, by overcoming the obstacles faced by users of WDM technology today, providing a starting platform that scales smoothly and protecting the investment. A user can commence with the more cost-effective CWDM technology and then later add DWDM in the when the capacity is required. FS.COM FMU series WDM solution makes the process even easier and more flexible. For more information, please visit or contact

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