Category Archives: Optical Solutions

How to Handle Challenges of CWDM Testing?


CWDM technology has proven itself to be a cost-effective and simplified method for network managers to optimize the existing infrastructure. The adoption of CWDM system into metro and regional network is constantly on the rise and it also extends the reach to the access networks. CWDM is becoming more widely accepted as an important transport architecture owing to its lower power dissipation, smaller size, and less cost. This article will focus on the challenges concerning CWDM testing, and provide several methods to help overcome them.

Basic Configurations of CWDM Network

CWDM configuration is usually based on a single-fiber pair: one fiber is for transmitting and the other for receiving. The following figure shows the most basic configuration of optical network with 4 channel CWDM MUX/DEMUX: it often delivers eight wavelengths, from 1471 nm to 1611 nm, with 20 nm apart. A CWDM architecture is quite simple. It only has passive components like multiplexers and demultiplexers, without any active elements such as amplifiers. However, using CWDM as a means of increasing bandwidth also brings network characterization and deployment challenges, which will be discussed in the following section.

cwdm basic configuration

Challenges and Solutions for CWDM Testing

The challenges of CWDM testing mainly lie in three phases: construction and installation, system activation and upgrade or troubleshoot. Here we provide solutions for each.

Challenge One: Construction and Installation

During construction and installation process, it is essential to conduct physical-layer tests on the fiber from the head-end to the destination. Single-ended testing with an OTDR is definitively an advantage as it optimizes labor resources. In this case, the objectives are to characterize the entire link (not only the fiber) to include the add-drop multiplexers (OADM) and to guarantee continuity up to the final destination. However, testing at standard OTDR wavelengths, such as 1310 nm and 1550 nm, cannot be done in such conditions as these wavelengths are filtered out at either OADM, never reaching the end destination. Then how to test such a link?

cwdm otdr testing

Solution: Adopting a specialized CWDM OTDR. With CWDM-tuned wavelength, the CWDM OTDR is capable of performing an end-to-end test by dropping each test wavelength at the correspondent point on the network, allowing the characterization of each part of the network directly from the head-end. Which is considered time and labor saving since one don’t have to access. It also helps to speed up the deployment process as the technician will test all drop fibers from a single location.

Challenge Two: System Activation

Since CWDM architecture is rather basic which contains no active components like amplifiers, the only things that can prevent proper transmission in a CWDM system are transmitter failure, sudden change in the loss created in an OADM or manual errors, bad connections for example. To deal with these problems, one has to look at the signal being transmitted.

Solution: A CWDM channel analyzer is ideal to handle this challenge. It works to quickly determine the presence or absence of each of the 16 wavelengths and their power levels. Many CWDM OADM have tap ports, which means that there is a port where a small portion of the signal is dropped. Taps are typically 20 dB weaker than the main signal. If these taps are not present, a CWDM analysis should be performed. It consists of unplugging the end user to use the main feed for the analysis. To be ready for all possibilities, a CWDM channel analyzer should cover a power range going as low as –40 dBm, while being able to test the entire wavelength range in the shortest time as possible.

Challenge Three: Upgrade or Troubleshoot

In the maintenance and troubleshoot phrase, when the network is live and a new wavelength is added, one should figure out two questions: is the link properly set up? And is my wavelength presents and well?

out-of-band testing of cwdm

Solution: Two approaches are available to check if a link is set up properly: a CWDM OTDR approach or an out-of-band approach. The CWDM OTDR approach is relatively simple when a new customer is added. With CWDM OTDR, one can perform CWDM testing without having to wait for the customer or to go to the cell tower sites. The wavelength can be turned on at the head-end. Which speed testing process greatly.

The OTDR and channel analyzer combo are also useful when a single customer has issues. The channel analyzer will reveal if the channel is indeed present and within power budget. If not, the CWDM OTDR can be used to test at that specific wavelength or an out-of-band 1650 nm OTDR test can be performed from the customer’s site to detect any anomalies on the link, all without disconnecting the head-end since the OADM will filter out the 1650 nm, therefore not affecting the remainder of the network.


CWDM testing challenges may be inevitable during each phase of the deployment, but with specialized equipment, these challenges can be overcomed completely. Tools including a CWDM OTDR, a CWDM channel analyzer and an out-of band OTDR are proved effective and valuable to reduce downtime and increase bandwidth at a minimum cost.

5 Concepts Help Easily Get WDM System

The Wavelength Division Multiplexing (WDM) system is a passive, optical solution for increasing the flexibility and capacity of existing fiber lines in high-speed networks. By adding more channels onto available fibers, the WDM System enables greater versatility for data communications in ring, point-to-point, and multi-point topologies for both enterprise and metro applications. Do you know about WDM system? 5 concepts provided in this blog may help you easily get it.

Optical Transmission
Optical transmission is the conversion of a digital stream of information to light pulses. The light pulses are generated by a laser source (LED or vessel) and transmitted over an optical fiber. The receiver converts the light pulses back to digital information.

Optical Transmission

Wavelength Division Multiplexing
WDM is based on the fact that optical fibers can carry more than one wavelength at the same time. The lasers are transmitting the light pulses at different wavelengths that are combined via filters to one single output fiber. The device used to combine wavelengths is called multiplexer and the device used to separate wavelengths is called demultiplexer, which are the two most basic component in WDM system.

Wavelength Division Multiplexing

Optical Amplifiers
An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. Optical amplifiers boosts the attenuated wavelengths and are more cost efficient than electrical repeaters. Without amplifiers the reach is limited to 80-100km before electrical regeneration. Amplifier stations typically each 80-100km.

Depending on signal types and fiber characteristics, amplifiers are used in DWDM networks and increases the reach of the optical signals up to 3000 km. Amplifiers are an basic building block for a powerful DWDM network.

Optical Amplifiers

Transponders provides wavelength conversion from client to WDM signal. A transponder maps a single client to a single WDM wavelength. The digital framing of a line signal from a transponder provides service monitoring, management connectivity and increased reach. The broad range of available transponders enables cost efficient solutions for both CWDM & DWDM.


Optical Add Drop Multiplexer
The main function of an optical multiplexer is to couple two or more wavelengths into the same fiber. If a demultiplexer is placed and properly aligned back-to-back with a multiplexer, it is clear that in the area between them, two individual wavelengths exist. This presents an opportunity for an enhanced function, one in which individual wavelengths could be removed and also inserted. Such a function would be called an Optical Add Drop Multiplexer (OADM). OADM is used for increased flexibility in the optical paths. Services can be redirected upon failure or capacity constraints and capacity can be increased dynamically per node.


Multiplexer and demultiplexer are the most basic component in WDM system. If your transmission distance is more than 100 km, an optical amplifier is necessary. If your client wavelength isn’t available for WDM applications, you may need a transponder to convert it to WDM available wavelength. Want to achieve a more flexible, just choose to use a OADM. Besides these, sometimes, a dispersion compensation module is also needed to fix the form of optical signals that are deformed by chromatic dispersion and compensates for chromatic dispersion in fiber that causes the light pulses to spread and generate signal impairment. Do you get WDM system? Just start to build your own WDM system now!

Full CWDM Mux Demux and CWDM SFP Transceivers Solutions

CWDM systems have channels at wavelengths spaced 20 nanometers (nm) apart, compared with 0.4 nm spacing for DWDM. This allows the use of low-cost, uncooled lasers for CWDM. In a typical CWDM system, laser emissions occur on full eighteen channels at eighteen defined wavelengths: 1610 nm, 1590 nm, 1570 nm, 1550 nm, 1530 nm, 1510 nm, 1490 nm, 1470 nm, 1450 nm, 1430 nm, 1410 nm, 1390 nm, 1370 nm, 1350 nm, 1330 nm, 1310 nm, 1290 nm, 1270 nm. Besides, for CWDM systems an industry standard color coding scheme is used. The latches of the transceivers match the colored port indicators on the passive units therefore guaranteeing simple setup. Following color codes and wavelength are valid for CWDM.


Full CWDM Channels (18 Channels) Mux Demux Solution

The WDM system uses a multiplexer at the transmitter to combine several wavelengths together, each one carry different signal with bite-rate up to 10G and a demultiplexer at the receiver to split them apart. Both mux and demux are passive, requiring no power supply. The 18 Channels CWDM mux demux covers all channels of 1270nm to 1610nm in 20nm increments. Without replacing any infrastructure, it totally support data rates up to 180 Gbps by being completely protocol transparent. The main fields of applications are the use in SDH (STM-1, STM-4, STM-16, STM- 64), IP (Fast Ethernet, Gigabit Ethernet, 10 Gigabit) ATM and storage (1G, 2G, 4G, 8G, 10G Fibre Channel) networks. Connectors, located on the front of the CWDM mux demux modules, are labeled and use the same color-coding that is used to indicate the wavelength of the individual CWDM SFP transceivers (shown in the figure below).


When fiber availability is limited, CWDM mux demux could increase the bandwidth on the existing fiber infrastructure. By using 18ch CWDM mux demux mentioned above and the CWDM SFP transceivers, up to 180 Gbps could be supported on a fiber pair.


Full CWDM SFP Transceivers Solution

CWDM SFP transceiver is based on the SFP form factor which is a MSA standard build. The max speed of this product is 1.25G and they are also available as 2.5G and of course the popular CWDM 10G SFP transceivers. The CWDM SFP transceiver has a specific laser which emits a “color” defined in the CWDM ITU grid. The CWDM ITU grid is defined from 1270 to 1610nm and has steps of 20nm. So the available wavelength is 1270nm, 1290nm, 1310nm, 1330nm, 1350nm, 1370nm, 1390nm, 1410nm, 1430nm, 1450nm, 1470nm, 1490nm, 1510nm, 1530nm, 1550nm, 1570nm, 1590nm and C. Besides, our CWDM SFP transceivers are similarly color-coded as the CWDM mux demux to help you match the right link connection (shown in the figure below).


We can make the CWDM SFP transceivers compatible with every brand (Cisco, HP, H3C, Juniper, Huawei, Brocade, Arista). A lot of brands have vendor locking and only with the proper coding. Fiberstore is specialized in this rebranding or recoding. We have many different switches and routers in our test lab to test the coding. We also use different Optical Spectrum Analyzers to ensure the CWDM SFP transceiver is emitting the right color and has the correct power budget. The CWDM SFP transceiver is used in combination with passive CWDM mux demux, and we can provide you a complete solution and advice on which equipment fits best in your project. Please give us your project details and we will provide the most efficient and economical solution.

1270nm SFP 1290nm SFP 1310nm SFP 1330nm SFP 1350nm SFP 1370nm SFP
1390nm SFP 1410nm SFP 1430nm SFP 1450nm SFP 1470nm SFP 1490nm SFP
1510nm SFP 1530nm SFP 1550nm SFP 1570nm SFP 1590nm SFP 1610nm SFP

Use Cisco Compatible DWDM SFP+ to Connect DWDM Transport to Your Cisco 10G Switches

Dense Wavelength Division Multiplexing (DWDM) enables carrier’s networks to accommodate many hundreds of aggregated services of any sub-rate protocol without installing additional dark fiber. DWDM SFP+ transceiver is mainly manufactured for carriers and large enterprises that need a scalable, flexible, cost-effective system for multiplexing, transporting and protecting high-speed data, storage, voice and video applications. The Cisco compatible 10G DWDM SFP+ transceiver modules are fiber line cards for a wide variety of Cisco switches, routers, and other equipment. They allow enterprises and service providers to provide scalable and easy-to-deploy 10-Gbps LAN, WAN, and optical transport network (OTN) services in their networks.

According to DWDM ITU (ITU-T G.694.1) channels, Cisco DWDM SFP+ transceivers are provided with 40 channels, from C20 1561.41nm to C59 1530.33nm (shown in the table below).

PN. ITU Channel PN. ITU Channel PN. ITU Channel
DWDM-SFP10G-61.41 C20 1561.41 nm DWDM-SFP10G-50.12 C34 1550.12 nm DWDM-SFP10G-38.98 C48 1538.98 nm
DWDM-SFP10G-60.61 C21 1560.61 nm DWDM-SFP10G-49.32 C35 1549.32 nm DWDM-SFP10G-38.19 C49 1538.19 nm
DWDM-SFP10G-59.79 C22 1559.79 nm DWDM-SFP10G-48.51 C36 1548.51 nm DWDM-SFP10G-37.40 C50 1537.40 nm
DWDM-SFP10G-58.98 C23 1558.98 nm DWDM-SFP10G-47.72 C37 1547.72 nm DWDM-SFP10G-36.61 C51 1536.61 nm
DWDM-SFP10G-58.17 C24 1558.17 nm DWDM-SFP10G-46.92 C38 1546.92 nm DWDM-SFP10G-35.82 C52 1535.82 nm
DWDM-SFP10G-57.36 C25 1557.36 nm DWDM-SFP10G-46.12 C391546.12 nm DWDM-SFP10G-35.04 C53 1535.04 nm
DWDM-SFP10G-56.55 C26 1556.55 nm DWDM-SFP10G-45.32 C40 1545.32 nm DWDM-SFP10G-34.25 C54 1534.25 nm
DWDM-SFP10G-55.75 C27 1555.75 nm DWDM-SFP10G-44.53 C41 1544.53 nm DWDM-SFP10G-33.47 C55 1533.47 nm
DWDM-SFP10G-54.94 C28 1554.94 nm DWDM-SFP10G-43.73 C42 1543.73 nm DWDM-SFP10G-32.68 C56 1532.68 nm
DWDM-SFP10G-54.13 C29 1554.13 nm DWDM-SFP10G-42.94 C43 1542.94 nm DWDM-SFP10G-31.90 C57 1531.90 nm
DWDM-SFP10G-53.33 C30 1553.33 nm DWDM-SFP10G-42.14 C44 1542.14 nm DWDM-SFP10G-31.12 C58 1531.12 nm
DWDM-SFP10G-52.52 C31 1552.52 nm DWDM-SFP10G-41.35 C45 1541.35 nm DWDM-SFP10G-30.33 C59 1530.33 nm
DWDM-SFP10G-51.72 C32 1551.72 nm DWDM-SFP10G-40.56 C46 1540.56 nm
DWDM-SFP10G-50.92 C33 1550.92 nm DWDM-SFP10G-39.77 C47 1539.77nm

In fact, mot all Cisco switches can be supported for DWDM SFP+ transceivers. According to Cisco 10-Gigabit Ethernet Transceiver Modules Compatibility Matrix, there are 72 types of Cisco switches are available to support DWDM SFP+ transceivers. But only 19 of them can support be supported all 40 channels DWDM SFP+ transceivers (shown in the table below).

Switches Series Models
Cisco Nexus 3000 Series N3K-C3016Q-40GE, N3K-C3064PQ-10GE, N3K-C3064TQ-10GT, N3K-C3064PQ-10GX
Cisco Nexus 3100 Series N3K-C3132Q-40GE, N3K-C3132Q-40GX, N3K-C3132Q-XL, N3K-C3132Q-V, N3K-C3172PQ-10GE, N3K-C3172TQ-10GT, N3K-C3172PQ-XL, N3K-C3172PQ-XL, N3K-C3172TQ-XL, N3K-C31108PC-V, N3K-C31108PC-V
N3K-C31108TC-V, N3K-C31128PQ-10GE
Cisco Nexus 3200 Series N3K-C3264Q, N3K-C3232C
Cisco Nexus 3500 Series N3K-C3548P-10G , N3K-C3524P-10G, N3K-C3548P-10GX, N3K-C3524P-10GX

To build a complete DWDM network in your system, except for switches and DWDM SFP+ transceivers, you also usually need a DWDM mux/demux module. At present, DWDM mux/demux modules are available in 2 channels to 96 channels. Since Cisco DWDM SFP+ transceivers are available in 40 channels (from C20 1561.41nm to C59 1530.33nm ), now I will take 40 channels C20-C59 DWDM mux/demux module (show in the figure below) for example to explain how it works.

40 channels DWDM mux demux

Front panel of above 40 channels C20-C59 DWDM mux/demux module are shown in the figure below. Connectors, located on the front of the DWDM mux/demux modules, are labeled and use the same channel that is used to indicate the wavelength of the individual DWDM transceivers.

DWDM muxdemux
Use a pair of 40 channels C20-C59 DWDM mux/demux modules, 40 signals can be transmitted over one fiber pair, which greatly reduces the cabling cost.

40 DWDM muxdemux
Now, let’s use Cisco compatible DWDM SFP+ to connect DWDM transport to your Cisco 10G switches!

Cisco Compatible DWDM SFP+

CWDM Mux/Demux User Guide

When we demand for higher bandwidth, we often choose to install new fiber. However, that is an expensive solution. Then what should we do? Now this article will give you a less expensive solution—using CWDM Mux/Demux with CWDM transceivers, which may allow you to maximize capacity and increase bandwidth on existing fiber route by multiplexing several distinct signals or protocols over a single or duplex-fiber connection. The passive optical CWDM Mux/Demux usually utilizes a thin-film filter and circulator technology. They are available in various wavelength combinations based on the entire wavelength spectrum (1270nm–1610nm in 20nm increments) defined by the ITU G.694.2 CWDM standard. Accordingly, CWDM transceivers are also available in 1270nm–1610nm (20nm spacing).

Since CWDM Mux/Demux can support 18 wavelengths include 1270, 1290, 1310, 1330, 1350, 1370, 1390, 1410, 1430, 1450, 1470, 1490, 1510, 1530, 1550, 1570, 1590 and 1610 nano-meters. Therefore, in the market, the channels of CWDM Mux/Demux varies from 2 channels to 18 channels. In this article, we may introduce these 4 channels CWDM Mux/Demux in detail. Using methods of other channel CWDM Mux/Demux can all reference 4 channels CWDM Mux/Demux.4 channels CWDM Mux/Demux is available in any four wavelengths from 1270nm–1610nm (20nm spacing). At present, CWDM Mux/Demux is available in dual fiber and single fiber two types. In the following passages, I will take 4 channels 1510-1570nm dual fiber CWDM Mux/Demux and 4 channels 1470-1590nm single fiber CWDM Mux/Demux for example to tell you how to use them in your network.

4 Channels 1510-1570nm Dual Fiber CWDM Mux/Demux User Guide
To install a  4 channels 1510-1570nm dual fiber CWDM Mux/Demux in your network, you need a pairs of  4 channels 1510-1570nm dual fiber CWDM Mux/Demux. For dual fiber link  CWDM Mux/Demux, the Mux/Demux are always the same (shown in the following picture).

CWDM Mux/Demux User Guide

Just shown as the following picture. To install a  4 channels 1510-1570nm dual fiber CWDM Mux/Demux in your network, you just need a pair of 4 channels 1510-1570nm dual fiber CWDM Mux/Demux, a 1510nm SFP, 1530nm SFP1550nm SFP and a 1570nm SFP.

4 Channels 1510-1570nm Dual Fiber CWDM MuxDemux

4 Channels 1470-1590nm Single Fiber CWDM Mux/Demux User Guide
To install a  4 channels 1470-1590nm single fiber CWDM Mux/Demux in your network, you also need a pairs of  4 channels single fiber CWDM Mux/Demux. But for single fiber Mux/Demux, they are not the same. If you install a  4 channels 1470-1590nm single fiber CWDM Mux/Demux on one end, you may need to install a 4 channels 1490-1610nm single fiber CWDM Mux/Demux on the other end (shown in the following picture).

CWDM Mux/Demux User Guide

Just shown as the following picture. To install a  4 channels 1470-1590nm single fiber CWDM Mux/Demux in your network, you need a 4 channels 1470-1590nm single fiber CWDM Mux/Demux and 4 channels 1490-1610nm single fiber CWDM Mux/Demux pair. And a 1470nm SFP, 1510nm SFP, 1550nm SFP and 1590nm SFP for 4 channels 1470-1590nm single fiber CWDM Mux/Demux. A 1490nm SFP, 1530nm SFP, 1570nm SFP, 1610nm SFP for  4 channels 1490-1610nm single fiber CWDM Mux/Demux.

Single-Fiber CWDM Mux Demux Application

The Latest Generation of PON – NG-PON2

To meet the large demand for high capacity transmission in optical access systems, 10G-PON (10G Passive Optical Network) has already been standardized by IEEE (Institute of Electrical and Electronics Engineers) and ITU (International Telecommunication Union). To enable the development of future optical access systems, the most recent version of PON known as NG-PON2 (Next-Generation Passive Optical Network 2) was approved recently, which provides a total throughput of 40 Gbps downstream and 10 Gbps upstream over a single fiber distributed to connected premises. The migration from GPON to 10G-PON and NG-PON2 is the maturity of technology and the need for higher bandwidth. This article will introduce the NG-PON2 technology to you.


What Is NG-PON2?
NG-PON2 is a 2015 telecommunications network standard for PON which was developed by ITU. NG-PON2 offers a fiber capacity of 40 Gbps by exploiting multiple wavelengths at dense wavelength division multiplexing (DWDM) channel spacing and tunable transceiver technology in the subscriber terminals (ONUs). Wavelength allocations include 1524 nm to 1544 nm in the upstream direction and 1596 nm to 1602 nm in the downstream direction. NG-PON2 was designed to coexist with previous architectures to ease deployment into existing optical distribution networks. Wavelengths were specifically chosen to avoid interference with GPON, 10G-PON, RF Video, and OTDR measurements, and thus NG-PON2 provides spectral flexibility to occupy reserved wavelengths in deployments devoid of legacy architectures.

How Does NG-PON2 Work?
If 24 premises are connected to a PON and the available throughput is equally shared then for GPON each connection receives 100 Mbps downstream and 40 Mbps upstream over a maximum of 20 km of fiber. For 10G-PON, which was the second PON revision, each of the 24 connections would receive about 400 Mbps downstream and 100 Mbps upstream. The recently approved NG-PON2 will provide a total throughput of 40 Gbps downstream and 10 Gbps upstream over a maximum of 40 km of fiber so each of the 24 connections would receive about 1.6 Gbps downstream and 410 Mbps upstream. NG-PON2 provides a greater range of connection speed options including 10/2.5 Gbps, 10/10 Gbps and 2.5/2.5 Gbps. NG-PON2 also includes backwards compatibility with GPON and 10G-PON to ensure that customers can upgrade when they’re ready.

NG-PON2 Work Principle

NG-PON2 Advantages
The NG-PON2 technology is expected to be about 60 to 80 percent cheaper to operate than a copper based access network and provides a clear undeniable performance, capacity and price advantage over any of the copper based access networks such as Fiber to the Node (FTTN) or Hybrid Fiber Coax (HFC). At present, three clear benefits of NG-PON2 have been proved. They are a 30 to 40 percent reduction in equipment and operating costs, improved connection speeds and symmetrical upstream and downstream capacity.

Reduced Costs
NG-PON2 can coexist with existing GPON and 10G-PON systems and is able to use existing PON-capable outside plant. Since the cost of PON FTTH (Fiber to the Home) roll out is 70 percent accounted for by the optical distribution network (ODN), this is significant. Operators have a clear upgrade path from where they are now, until well into the future.

Improved Connection Speeds
Initially NG-PON2 will provide a minimum of 40 Gbps downstream capacity, produced by four 10 Gbps signals on different wavelengths in the O-band multiplexed together in the central office with a 10 Gbps total upstream capacity. This capability can be doubled to provide 80 Gbps downstream and 20 Gbps upstream in the “extended” NG-PON2.

Symmetrical Upstream and Downstream Capacity
Both the basic and extended implementations are designed to appeal to domestic consumers where gigabit downstream speeds may be needed but more modest upstream needs prevail. For business users with data mirroring and similar requirements, a symmetric implementation will be provided giving 40/40 and 80/80 Gbps capacity respectively.

With the introduction of NG-PON2, there is now an obvious difference between optical access network and copper access network capabilities. Investment in NG-PON2 provides a far cheaper network to operate, significantly faster downstream and upstream speeds and a future-proof upgrade path all of which copper access networks do not provide, thus making them obsolete technologies. Telephone companies around the world have been carrying out trials of NG-PON2 and key telecommunication vendors have rushed NG-PON2 products to market.


From O to L: the Evolution of Optical Wavelength Bands

In optical fiber communications system, several transmission bands have been defined and standardized, from the original O-band to the U/XL-band. The E- and U/XL-bands have typically been avoided because they have high transmission loss regions. The E-band represents the water peak region, while the U/XL-band resides at the very end of the transmission window for silica glass.

Optical Wavelength Bands

Intercity and metro ring fiber already carry signals on multiple wavelengths to increase bandwidth. Fibers entering the home will soon do the same. Now there are several types of optical telecom systems have been developed, some based on time division multiplexing (TDM) and others on wavelength division multiplexing (WDM), either dense wavelength division multiplexing (DWDM) or coarse wavelength division multiplexing (CWDM). This article may represent the evolution of optical wavelength bands mainly by describing these three high-performance systems.

Dense Wavelength Division Multiplexing
DWDM systems were developed to deal with the rising bandwidth needs of backbone optical networks. The narrow spacing (usually 0.2 nm) between wavelength bands increases the number of wavelengths and enables data rates of several Terabits per second (Tbps) in a single fiber.

These systems were first developed for laser-light wavelengths in the C-band, and later in the L-band, leveraging the wavelengths with the lowest attenuation rates in glass fiber as well as the possibility of optical amplification. Erbium-doped fiber amplifiers (EDFAs, which work at these wavelengths) are a key enabling technology for these systems. Because WDM systems use many wavelengths at the same time, which may lead to much attenuation. Therefore optical amplification technology is introduced. Raman amplification and erbium-doped fiber amplifiers are two common types used in WDM system.


In order to meet the demand for “unlimited bandwidth,” it was believed that DWDM would have to be extended to more bands. In the future, however, the L-band will also prove to be useful. Because EDFAs are less efficient in the L-band, the use of Raman amplification technology will be re-addressed, with related pumping wavelengths close to 1485 nm.

Coarse Wave Division Multiplexing
CWDM is the low-cost version of WDM. Generally these systems are not amplified and therefore have limited range. They typically use less expensive light sources that are not temperaturestabilized. Larger gaps between wavelengths are necessary, usually 20 nm. Of course, this reduces the number of wavelengths that can be used and thus also reduces the total available bandwidth.


Current systems use the S-, C- and L-bands because these bands inhabit the natural region for low optical losses in glass fiber. Although extension into the O and E-band (1310 nm to 1450 nm) is possible, system reach (the distance the light can travel in fiber and still provide good signal without amplification) will suffer as a result of losses incurred by use of the 1310 nm region in modern fibers.

Time Division Multiplexing
TDM systems use either one wavelength band or two (with one wavelength band allocated to each direction). TDM solutions are currently in the spotlight with the deployment of fiber-to-the-home (FTTH) technologies. Both EPON and GPON are TDM systems. The standard bandwidth allocation for GPON requires between 1260 and 1360 nm upstream, 1440 to 1500 nm downstream, and 1550 to 1560 nm for cable-TV video.

To meet the rise in bandwidth demand, these systems will require upgrading. Some predict that TDM and CWDM (or even DWDM) will have to coexist in the same installed network fibers. To achieve this, work is underway within the standardization bodies to define filters that block non-GPON wavelengths to currently installed customers. This will require the CWDM portion to use wavelength bands far away from those reserved for GPON. Consequently, they will have to use the L-band or the C- and L-bands and provided video is not used.


In each case, sufficient performance has been demonstrated to ensure high performance for today’s and tomorrow’s systems. From this article, we know that the original O-band hasn’t satisfied the rapid development of high bandwidth anymore. And the evolution of optical wavelength bands just means more and more bands will be called for. In the future, with the growth of FTTH applications, there is no doubt that C- and L-bands will play more and more important roles in optical transmission system. Fiberstore offer all kinds of products for WDM optical network, such as CWDM/DWDM MUX DEMUX and EDFA. For more information, please visit

Erbium Doped Fiber Amplifier (EDFA) Used in WDM System

The capacity of fiber optical communication systems has undergone enormous growth during the last few years in response to huge capacity demand for data transmission. With the available wavelength division multiplexing (WDM) equipment, commercial system can transport more than 100 channels over a single fiber. However, increasing the number of channels in such systems will eventually result in the usage of optical signal demultiplexing components with greater values of optical attenuation. Besides, when transmitted over long distances, the optical signal is highly attenuated. Therefore, to restore the optical power budget, it is necessary to implement optical signal amplification. This article may mainly tell you  why EDFA is used in WDM system and how does it work.

Why Use EDFA in WDM System?

EDFA stands for erbium-doped fiber amplifiers, which is an optical amplifier that uses a doped optical fiber as a gain medium to amplify an optical signal. EDFA has large gain bandwidth, which is typically tens of nanometers and thus actually it is enough to amplify data channels with the highest data rates. A single EDFA may be used for simultaneously amplifying many data channels at different wavelengths within the gain region. Before such fiber amplifiers were available, there was no practical method for amplifying all channels between long fiber spans of a fiber-optic link. There are practically two wavelength widows C-Band (1530nm-1560nm) and L-Band (1560nm-1600nm). EDFA can amplify a wide wavelength range (1500nm-1600nm) simultaneously, which just satisfies the DWDM application, hence it is very useful in WDM for amplification.

How Does EDFA Work ?

The basic configuration for incorporating the EDFA in an optical fiber link is shown in the picture below. The signals and pump are combined through a WDM coupler and launched into an erbium-doped fiber (EDF). The amplified output signals can be transmitted through 60-100km before further amplification is required.

Erbium-doped fiber is the core technology of EDFA, which is a conventional silica fiber doped with erbium ions as the gain medium. Erbium ions (Er3+) are having the optical fluorescent properties that are suitable for the optical amplification. When an optical signal such as 1550nm wavelength signal enters the EDFA from input, the signal is combined with a 980nm or 1480nm pump laser through a wavelength division multiplexer device. The input signal and pump laser signal pass through erbium-doped fiber. Here the 1550nm signal is amplified through interaction with doped erbium ions. This can be well understood by the energy level diagram of Er3+ ions given in the following figure.


Where to Buy EDFA for Your WDM System ?

To ensure the required level of amplification over the frequency band used for transmission, it is highly important to choose the optimal configuration of the EDFAs. Before you buy a EDFA, keep in mind that the flatness and the level of the obtained amplification, and the amount of EDFA produced noise are highly dependent on each of the many parameters of the amplifier. Fiberstore provide many kinds of EDFAs, especially the DWDM EDFAs (shown in the picture below), which have many output options (12dBm-35dBm). Besides, they are very professional in optical amplifiers. Whatever doubts you have, they can give a clear reply.


Do You Know about Serial-to-Fiber Media Converters?

Due to the easiness of setup and low cost, serial devices are used around the world of industrial systems. However, the longer the copper cable, the more data corruption due to the electromagnetic (EMI) and radio frequency (RFI) interference. The fiber connection provides the benefits of noisy immunity and distance. Therefore, serial over fiber is the best solution to overcome these problems, and this text will give a brief introduction of serial-to-fiber media converters.

What Is a Serial-to-Fiber Media Converter?

Serial-to-Fiber Media ConvertersSerial-to-fiber media converters, sometimes also called fiber optic modem (FOM), is a device which provides electrical to optical conversion of electronic communication and data signals for transmission using tactical fiber optic cable assemblies. The converter simultaneously receives incoming optical signals and converts them back to the original electronic signal allowing for full duplex transmission. Together with the tactical fiber optic cables, the converter provides a rugged, secure, and easy deployable optical link. The serial-to-fiber media converter is available in both single and multi-channel configurations and supports both point-to-point and multi-point configurations.

Three Common Serial Interfaces

In order to get one step closer to understanding the serial-to-fiber media converters, common serial interfaces must be explained before. RS-232, RS-422, and RS-485 are the most popular serial interfaces in the industrial application. Each interface provides unique benefits for device communication. RS-232 is the most common serial interface and ships as a standard component on most Windows-compatible desktop computers. RS-422 is the serial connection used on Apple computers. RS-485 is a superset of RS-422 and expands on the capabilities. For your easy reference, a quick comparison chart listed below demonstrates the key differences of these three commonly used serial interfaces for industrial applications.

Specifications RS-232 RS-422 RS-485
Speed Full-duplex Full-duplex Half-duplex
Distance 15M@9600bps 1.2KM@9600bps 1.2KM@9600bps
Pins TxD, RxD, RTS, CTS, DTR, DSR, DCD, GND TxA, TxB, RxA, RxB, GND DataA, DataB, GND
Cable Cost High Medium Low
Topology Point-to-point Point-to-point Multidrop
Software Compatibility High Medium Lowest
Troubleshooting Easy Hard Hard

How Does It Work?

In terms of serial-to-fiber media converters, there are two kinds of connection mode: pair and ring. The working principles of them are different.
Pair Connection Mode
The Pair Connection simply extends the point-to-point transmission distance of the serial connection. Two serial-to-fiber converters can be connected over a fiber cable between a computer and a serial device. These two locations can be up to 12 miles (20 km) apart. Beware the flow control signals for RS-232 cannot be transmitted over fiber. The DTR/DSR and RTS/CTS need to be shortened for RS-232 application.

Pair Connection Mode serial-to-fiber media converter

Ring Connection Mode
If multiple serial devices need to be connected, the Ring Connection mode provides a cost-effective solution. The serial-to-fiber converters can inter-connect to the neighboring converters and form a closed fiber-to-serial ring. Data packets are transmitted by one converter to the other and so on until the signal returns to the converter that sent the original signal. When using the Ring Connection mode, the total length of the fiber connection is up to 62 miles (100 km). The only drawback is the failure of one fiber connection will cause the entire system to fail.

Ring Connection Mode serial-to-fiber converter


Now in the market, serial to fiber converters are available in several types depending upon the protocol selected, including RS-232 to Fiber Converter, RS-485 to Fiber Converter, RS-422 to Fiber Converter, RS-485/422 to Fiber Converter, and RS-485/422/432 to Fiber Converter. The applications of RS-232 and RS-485 converters are described as follows.
RS-232 Application
This serial to fiber Converter can be connected with RS485/RS422/RS232 port of computer or other devices, solve the problem of traditional RS485/RS422/RS232 communication conflict between distance and rate. RS-232 fiber converters can operate as asynchronous devices, support speeds up to 921,600 baud, and support a wide variety of hardware flow control signals to enable seamless connectivity with most serial devices. In this example, a pair of RS-232 converters provides the serial connection between a PC and Terminal Server allowing access to multiple data devices via fiber.

RS-232 serial-to-fiber converters
RS-485 Application
In this example application a pair of RS-485 converters provide the multi-drop connection between the Host equipment and the connected multi-drop devices via fiber.

RS-485 serial-to-fiber converters

Serial to fiber converter can provide transmission distance up to 2 km over multi-mode fiber and up to 60 km over single-mode fiber, which is really helpful for your network. If you want to know more about this converter, you can visit Fiberstore, which designs, manufactures, and sells all kinds of serial to fiber converters.

Introduction of Media Converter

There is no doubt that Ethernet fiber-optic communications provide many advantages over copper based Ethernet communications. These include immunity to noise and further distance capabilities. Systems that require fiber-optic communication can use switches that contain built-in fiber optic ports. However, if your switch does not have built-in fiber optic ports or does not have enough fiber-optic ports, then a media converter will be needed to convert copper based communications to fiber-optic communications. This article will review the different types of media converters and provide information on the wide variety of applications for media converters.

What is a Media Converter?

Media ConverterMedia converters are flexible and cost-effective devices for implementing and optimizing fiber links in all types of networks. Media converters enable you to connect different types of media, such as twisted pair, fiber, and coax, within a network. The most widely used converters are probably the ones used to convert computers UTP Ethernet ports to fiber. This enables you the ability extend your Ethernet network beyond the 100-meter limit imposed by copper cable. Besides, some other converters also convert multi-mode to single-mode, convert analog signals to digital, multiplex several signals over one fiber pair, or perform other signal processing. In a word, as a device to converter one media to another, media converters are really working.

Types of Media Converter

There are a wide variety of media converters available that support different network protocols, data rates, cabling and connector types. Two main kinds of media converters are copper-to-fiber media converter and fiber-to-fiber media converter.

Copper-to-Fiber Media Converters

The most common type of media converter is a device that functions as a transceiver, which is used to convert the electrical signal used in copper UTP network cabling into light waves used in fiber optic cabling. Fiber optic connectivity is necessary when the distance between two network devices exceeds the transmission distance of copper cabling. Copper-to-fiber conversion using media converters enables two network devices with copper ports to be connected over extended distances via fiber optic cabling.

Copper-to-Fiber Media Converter

  • Ethernet Copper-to-Fiber Media Converters
    Supporting the IEEE 802.3 standard, Ethernet copper-to-fiber media converters are used to provide connectivity for Ethernet, Fast Ethernet, Gigabit and 10 Gigabit Ethernet devices. Hence these converters are also usually divided into Fast Ethernet media converter, Gigabit media converter and 10 Gigabit media converter. The diagram below shows a typical application where Ethernet Media Converters connect to Ethernet Switches by way of Multimode fiber and UTP copper cabling.

Ethernet Media Converter

  • TDM Copper-to-Fiber Media Converters
    The most common TDM copper-to-fiber converters are T1/E1 and T3/E3 converters, which provide a reliable and cost-effective method to extend traditional TDM (Time Division Multiplexing) telecom protocols copper connections using fiber optic cabling. T3/E3 and T1/E1 converters usually operate in pairs extending distances of TDM circuits over fiber, improving noise immunity, quality of service, intrusion protection and network security.
  • Serial-to-Fiber Media Converters
    Serial-to-fiber converters provide fiber extension for serial protocol copper connections. They can automatically detect the signal baud rate of the connected Full-Duplex serial device, and support point-to-point and multi-point configurations.

Fiber-to-Fiber Media Converters

Fiber-to-fiber media converters can provide connectivity between multi-mode (MM) and single-mode (SM) fiber, between different power fiber sources and between dual fiber and single-fiber. In addition, they support conversion from one wavelength to another. Fiber-to-fiber media converters are normally protocol independent and available for Ethernet, and TDM applications.

  • Multi-mode to Single-mode Converters
    Enterprise networks often require conversion from MM to SM fiber, which supports longer distances than MM fiber. Mode conversion is typically required when lower cost legacy equipment uses MM ports but connectivity is required to SM equipment, a building has MM equipment, while the connection to the service provider is SM, and MM equipment is in a campus building but SM fiber is used between buildings.

Multi-mode to Single-mode Fiber Converters

  • Dual Fiber to Single-Fiber Converters
    Enterprise networks may also require conversion between dual and single-fiber, depending on the type of equipment and the fiber installed in the facility. Single-fiber is single-mode and operates with bi-directional wavelengths, often referred to as BIDI. Typically BIDI single-fiber uses 1310nm and 1550nm wavelengths over the same fiber strand in opposite directions. The development of bi-directional wavelengths over the same fiber strand was the precursor to Wavelength Division Multiplexing.

Dual Fiber to Single-Fiber Converters

Applications of Media Converter

Media converters do more than convert copper-to-fiber and convert between different fiber types. Media converters for Ethernet networks can support integrated switch technology, and provide the ability to perform 10/100 and 10/100/1000 rate switching. Additionally, media converters can support advanced bridge features which including VLAN, Quality of Service (QoS) prioritization, Port Access Control and Bandwidth Control and really facilitate the deployment of new data, voice and video to end users. Media converters can provide all these sophisticated switch capabilities in a small, cost-effective device.