Category Archives: WDM Optical Network

How to Light a DWDM Ring Beyond 10G?

Network layout nowadays is no longer limited by old rules created for early Ethernet networks. The technology and infrastructure devices available currently allows for different network topologies, including bus, star, ring and mesh networks. Each of them has its benefits and drawbacks and can be combined to suit application needs. This article emphasizes on the DWDM ring network configuration, illustrating the approaches to build a fiber ring beyond 10G.

What Is a DWDM Fiber Ring?

A fiber ring refers to the network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node. A ring configuration is designed to withstand a single failure. If there happens to be a failure, the system automatically reconfigure itself.

Similarly, 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.


How to Create a DWDM Fiber Ring Beyond 10G?

Assuming to build a higher than 10G optical ring using two strands of dark fibers, all nodes in this ring configuration are less than 10km apart and there are 8 nodes in total. Here we illustrate the options for achieving a DWDM ring beyond 10G.

20G Fiber Ring

For a 20G ring, the configuration is rather simple. There is no need for an OADM or Mux/Demux, it is recommend to use an Ethernet switch with two SFP+ ports and a pair of BIDI SFP+ optics.

Items Description
S5800-48F4S High Performance Data Center Switch (48*1GE+4*10GE)
10GBASE-BX SFP+ Generic Compatible 10GBASE-BX SFP+ 1270nm-TX/1330nm-RX 10km DOM Transceiver
10GBASE-BX SFP+ Generic Compatible 10GBASE-BX SFP+ 1330nm-TX/ 1270nm-RX 10km DOM Transceiver
40G Fiber Ring

There are three options for creating a 40G DWDM ring.

1. Use a switch with QSFP+ ports, and using QSFP+ optics in accordance. This can be the most cost-effective option for 40G if you have no future plan for more than 40G on the ring.

Items Description
S5850-48S6Q High Performance Data Center Switch (48*10GE+6*40GE)
40GBASE-LR4 Generic Compatible 40GBASE-LR4 and OTU3 QSFP+ 1310nm 10km LC Transceiver for SMF

2. Use four 10G SFP+ optics and a CWDM OADM. You could even scale up to 18 channels giving you a 180G ring if you were use all 18 CWDM channels and had that large of a OADM or Mux/Demux. First four channels with lower cost SFP+ optics, wavelength 1270nm through 1310nm. Then the next 14 channels 1350nm to 1610nm adopts SFP+ with relatively higher cost. You would need a SFP+ port per channel on both ends, and a passive CWDM OADM.

Items Description
CWDM OADM Single Fiber/ Dual Fiber CWDM OADM, East and West
10GBASE-LR SFP+ Generic Compatible 10GBASE-LR SFP+ 1310nm 10km DOM Transceiver
10GBASE-ER SFP+ Generic Compatible 10GBASE-ER SFP+ 1550nm 40km DOM Transceiver

3. Use 10G DWDM SFP+ optics and a DWDM OADM. You can choose less expensive 100Ghz optics that have up to 40 or 44 channels, or the expensive 50Ghz optics that can reach up to 80 or 88 channels.

Items Description
DWDM OADM Single Fiber/ Dual Fiber DWDM OADM, East and West
10G DWDM SFP+ Generic C40 Compatible 10G DWDM SFP+ 100GHz 1545.32nm 40km DOM Transceiver
10G DWDM SFP+ Generic H50 Compatible 10G DWDM SFP+ 50GHz 1537nm 40km DOM Transceiver
100G Fiber Ring

As for a 100G fiber ring, you can count on Ethernet switches that have 100G QSFP28 uplink ports, along with 100G QSFP28 optics. This would allow a 100G connection each way around the ring.

Items Description
S5850-48S2Q4C Carrier Grade 100G-uplink Switch (48*10GE + 2*40GE + 4*100GE)
100GBASE-LR4 Generic Compatible QSFP28 100GBASE-LR4 1310nm 10km Transceiver

Fiber ring enables more reliability and survivability: if a single link failure should occur – the traffic can simply be sent the other way around the ring. With the pervasiveness of Ethernet technology, the ring architecture is widely adopted to construct a Metropolitan Area Network (MAN), Metro-Ethernet service and school district that uses municipal fiber pathways. Several options for creating fiber ring beyond 10G are presented, along with the optical components needed. Hope this could be informative enough.

40G vs 100G: Which One Is Worth the Investment?

Today, the trend for high-speed data transmission and high-bandwidth is overwhelming. Some years ago, people had witnessed upgrading from 10Mbps Ethernet to 100Mbps Ethernet. And the migration from 1G to 10G was happened not very long ago. But now, whether you believe it or not, prepared or not prepared, 40G and 100G have already on the way. To upgrade to 40G or skip it and directly migrate to 100G has become a question for many data center mangers and IT engineers. Here, in this article, you may find some clue you want.

The Rise of 100G

To begin with, it has to be made clear that the market trend is 100G Ethernet, which will eventually become the mainstream in the future. The strong demand in 100G Ethernet is being driven by cloud services and hyper-scale data centers. And there is a demand for lower-priced 100G pluggable transceivers from data center customers. Currently, the market transition to 100GE is in full swing, fueled primarily by the seemingly insatiable need for networking bandwidth by hyper-scale data centers and cloud services. As it has been shown in the picture below, 100G Ethernet transceivers will exceed 15 million units a year.

100G market

This tremendous growth in deployments by a small number of key customers, together with a large number of suppliers competing for these orders, will undoubtedly drive down the cost of 100GE modules rapidly. It is predicted that the cost of 100G transceiver is expected to decline by 75% in the next couple of years. In the meantime, Facebook has publicly set a target cost of $100 for a 100G transceiver with a reach of less than 2km. While the Facebook target appears to be years away, we believe that a 70% cost reduction in 2 years is possible. By that time, the 100G transceivers will be more affordable.

Why not 40G?

If you ask me why 40G Ethernet will be obsolete? The short answer is “cost”. From the technical point, The primary issue lies in the fact that 40G Ethernet uses 4x10G signalling lanes. On UTP, 40G uses 4 pairs at 10G each. Early versions of the 40G standard used 4 pairs, but rapid advances in manufacturing developed a 4x10G WDM on a single fiber optic pair. Each 40G SFP module contains a silicon chip that performs multiplexing so that the switch see 40 gigabits in and 40 gigabits out. It’s similar to Coarse Wave Division Multiplexing when using fiber. When you buy a 40G cable or QSFP, you are paying for the cost of the chip and software, plus the lasers, etc. When using 25/50/100G, the “lane speed” is increased to 25 gigabits per second. For 100G Ethernet, there are four 25G signalling lanes. It’s cheaper to buy 100G with four lanes rather than 40G with a four-lane MUX.


Scale up to 100G with FS 100G Optics Solution

As one of the leading providers in optical communication , FS provides customers with 100G optics that are manufactured at the highest quality of standards in the industry, including QSFP28, CFP, CFP2, CFP4, 100G patch panels, 100G switches, etc. Part of the products are listed as follow:

Model ID Description    Price


Juniper JNP-QSFP-100G-SR4 Compatible 100GBASE-SR4 850nm 100m Transceiver

   US$  269


Cisco Compatible QSFP28 100GBASE-SR4 850nm 100m Transceiver

   US$  269


Juniper Networks CFP-100GBASE-SR10 Compatible 100GBASE-SR10 850nm 150m Transceiver

   US$  1,500

100G Ethernet are racing to market and will finally takeover the 40G market. Don’t hesitate to migrate your network to the 100G Ethernet to embrace the future technology.

Introduction to WDM Transponders

With the development of wavelength-division multiplexing (WDM) technology, the network traffic volume is increasing and the demand for more network bandwidth is also on the rise. By converting the operating wavelength of the incoming bitstream to an ITU-compliant wavelength, WDM transponder serves as a key component in WDM system. As an important technology in the fiber optical network, WDM is moving beyond transport to become the basis of all-optical networking. And how to optimize WDM network has always been a hot topic. The transponder is a device to optimize the performance of WDM network, which plays an important in the whole system of WDM network. This article will introduce you the information on WDM transponders.

What Is a WDM Transponder?

Also called as an OEO (optical-electrical-optical) transponder, a WDM transponder is an optical-electrical-optical wavelength converter, which has been widely adopted in a variety of networks and applications. The picture below shows us how a bidirectional transponder works. In this picture, the transponder is located between a client device and a DWDM system. And we can see clearly that, from left to right, the transponder receives an optical bitstream operating at one particular wavelength (1310 nm), and then converts the operating wavelength of the incoming bitstream to an ITU-compliant wavelength and transmits its output into a DWDM system. On the receive side (right to left), the process is reversed. The transponder receives an ITU-compliant bit stream and converts the signals back to the wavelength used by the client device.

WDM transponder

The Application of a WDM Transponder

According to its function, the application of a WDM transponders can be classified into the following types.

  • Wavelength Conversion. It is known to us that when a CWDM Mux/Demux or DWDM Mux/Demux is added into a WDM network, there is a requirement to convert optical wavelengths like 850nm, 1310nm and 1550nm to CWDM or DWDM wavelengths. Then the OEO transponder comes to assist. The OEO transponder receives, amplifies and re-transmits the signal on a different wavelength without changing the signal content.
  • Fiber Mode Conversion. Multimode fiber optic cables (MMF) are often used in short distance transmission, while single-mode fiber optic cables (SMF) are applied in long optical transmission. Therefore, in some network deployment, considering the transmission distances, MMF to SMF or SMF to MMF conversions are needed. WDM transponders can convert both multimode fiber to single-mode fiber and dual fiber to single fiber.
  • Signal Repeating. In long haul fiber optic transmission, WDM transponder also can work as repeaters to extend network distance by converting wavelengths (1310nm to 1550nm) and amplifying optical power. The OEO converters convert the weak optical signals from the fiber into electrical signals, and regenerate or amplify, then recover them into strong optical signals for continuous transmission.
WDM Transponder and FMT Solution

At FS, OEO transponders are made into small plug-in cards to be used on the FMT platform. FMT platform makes devices like EDFA, OEO, DCM, OLP and VOA into plug-in cards and provides standard rack units as well as free software to achieve better management and monitoring. In addition, FMT series products like OEO, DCM and OLP also have higher performance than that of old ones. FMT series OEO transponder can convert optical signals into DWDM wavelengths, reducing the fault risk caused by high power consumption of DWDM fiber optic transceiver. Since the OEO transponder is made into small plug-in card in the FMT platform, it only occupies one slot in the special designed chassis when installed, thus saving a lot of space. In addition, all these FMT plug-in cards, including OEO, in a rack unit share the same power source and support hot plug & play operation. And they can be inserted or removed flexibly in the racks for DWDM networking.



Since the OEO transponder plays an important role in WDM network, such as receiving, amplifying and re-transmitting the signal on a different wavelength, adding an OEO transponder into the WDM network is very essential. The OEO transponders in our FMT series are made into small plug-in cards with high quality to ensure good transmission performance. For more information on our FMT system, please visit

Brief Introduction to EDFA

In fiber optic communication systems, problems arise from the fact that no fiber material is perfectly transparent. The visible-light or infrared beams carried by a fiber are attenuated as they travel through the material. This necessitates the use of optical amplifiers. And EDFA (Erbium Doped Fiber Amplifier) is a representative one in the optical amplifier. There is one saying that EDFA is the most popular optical amplifier in optical network communications. Next, we will begin with the definition of EDFA.

The Definition of EDFA

An EDFA, also called optical amplifier or an erbium-doped fiber amplifier or erbium amplifier, is an optical or IR (Infrared Radiation) repeater that amplifies a modulated laser beam directly, without opto-electronic and electro-optical conversion. The device uses a short length of optical fiber doped with the rare-earth element erbium. When the signal-carrying laser beams pass through this fiber, external energy is applied, usually at IR wavelengths. This so-called pumping excites the atoms in the erbium-doped section of optical fiber, increasing the intensity of the laser beams passing through. The beams emerging from the EDFA retain all of their original modulation characteristics, but are brighter than the input beams.

Three Major Applications for Optical AmplifierThree Major Applications for Optical Amplifier

The above picture illustrates the three major applications for optical fiber amplifiers: booster, in-line amplifier, and pre-amplifier. These applications are described in more details below:

Booster Amplifier

Booster amplifiers are placed directly after the optical transmitter. In this application, booster amplifier is adopted to compensate for the losses of optical elements between the laser and optical fibers so that the increased transmitter power can be used to go further in the link.

In-line Amplifier

In-line amplifiers or in-line repeaters are placed along the transmission link to compensate for the losses incurred during propagation of optical signal. They take a small input signal and boost it for re-transmission down the fiber. Here it should also be pointed out that to control the signal performance and the noise added by the EDFA is important, because noise added by amplifier will limit the system length.


Pre-amplifiers are placed just before the receiver to increase the signal level before the photodetection takes place in an ultra-long haul system so as to improve receiver sensitivity. By placing a pre-amplifier, a much larger signal can be presented to the receiver, thus easing the demands of the receiver design.

Top EDFA Products Overview

By now, you should have a basic idea of what an EDFA is and what it is used for, next I will introduce you some truly excellent EDFA products on the market.

22dBm Output Booster DWDM EDFA C-band 24dB Gain, 1U Rack Mount
16dBm Output Mid-stage DWDM EDFA C-band 26dB Gain, Plug-in Card for FMT Multi-Service Transport System
17dBm Output Mid-stage DWDM EDFA C-band 17dB Gain, Plug-in Card for FMT Multi-Service Transport System

Of the various technologies available for optical amplifiers, EDFA technology is the most advanced, and consequently the vast majority of optical amplifiers are designed based on this technology. In addition, the combination of reliable performance and relatively low cost allows EDFA to be widely deployed in modern optical networks.

Optical Facility Protection for WDM Network

Wavelength-division multiplexing (WDM) is nothing new to us. It is a technology that multiplexes multiple optical signal on a single optical fiber by using different wavelengths of laser light. The multiple transmission paths involved in WDM network effectively relieve fiber exhaustion and extend link capacity, but they also make facility protection more essential than ever, because solid facility protection is the key to the availability of the link and the data being transmitted. This article introduces two methodologies that proven to be valid for optical link protection: electrical switching and optical switching.

Why Facility Protection is Essential to WDM Network?

With the explosion of information, the demand for extremely high-capacity data transmission began to soar. Enterprises and companies were asked to deliver greater volumes of traffic at much higher rates. Which spurs the need to store data in different facilities and to transport these data over different paths, so that if any network failure or downtime occurs, they can soon recover and keep the business running. In a properly protected WDM network, customers will have two or more sites that are connected to each other by diver paths, ensuring the availability and reliability of the network all the time. But fiber may break for many reasons including damage from the physical environment and human faults. Thus facility protection becomes vitally important.

Effective Facility Protection Methods for WDM Network

There are basically two methods for optical facility protection: one is electrical switching which adopts a cross connect to duplicate and select the working or protecting path, with two independent optics involved per each path and two Mux/Demux. And the other is optical switching, unlike electrical switching, it typically uses an optical switch to select the working or protected path.

Electrical Switching

In electrical switching, each service is simultaneously transmitted and received from two dark fibers. The signal from the device on the left side is transmitted to both working and protecting fiber, then it is delivered to the end device on the right side.

facility protection with electrical switching

So how the cross connect duplicates the Tx signals and selects the working and protecting path (Rx) for the receiving signal? In fact, the Tx signal is sent through the cross connect and duplicated through both transponders. On the Rx direction, the cross connect switches the signal to the receiving optical power of the transponder.

electrical switching details

Optical Switching

An optical switch is involved in this method to duplicate the data to the working and protecting fiber with an optical splitter, and selecting the operating fiber according to the optical power signals of all the services. One of the distinct differences between optical switching and electrical switching is that it simply offers no protection for the WDM optic.

facility protection with optical switching

Electrical Switching vs. Optical Switching: How to Choose?

When applied for optical facility protection, both methods have their benefits and drawbacks. For electrical switching, the WDM optic is better protected since it uses two uplink transponders per service – one for working and the other for protecting. Since protection is delivered per service, once a single service needs to be switched, the other service won’t be disturbed. Moreover, electrical switching is suited for any network topologies, and no power budget loss is associated with this method. However, electrical switching generally adopted more WDM optics and an additional Mux/Demux, hence fewer services are available through each unit, and it inevitably increases total costs.

While for optical switching which does not offer protection for WDM optic, more ports are available to transport services on each unit. Besides, no additional Mux/Demux is required in this method, so the overall cost of the solution can be decreased. The drawbacks of this method are that the optical switch lowers the optical power budget of the link. And optical switching is not suited for ring topologies for the fact that add and drop functionality is not available per wavelength.


Optical facility protection impacts the link availability, performance and reliability to a large extent. Your choice on facility protection method should always base on your specific needs, and taking power budget, network topology and cost into consideration. I hope this article would be helpful for you to make an informed decision.