How Much Do You Know About 100G DWDM Transceiver?

The pace of the development of network technology has never stopped, from Fast Ethernet to Gigabit Ethernet, 10G Ethernet, 40G Ethernet and 100G Ethernet. To keep up with the pace, many data centers has deployed 100G network. We know that there are many types of 100G transceivers, such as 100G CFP/CFP2/CFP4, CXP and 100G QSFP28. Recently, new 100G DWDM technology has been the choice for 100G network applications over long distance. There are two types of 100G DWDM transceivers—Coherent 100G DWDM transceiver and PAM-4 (Pulse Amplitude Modulation) 100G DWDM transceiver. How much do you know about them? This article is going to give an introduction to 100G DWDM transceiver.

Coherent 100G DWDM Transceiver

Coherent 100G DWDM transceiver refers to coherent CFP transceiver. DWDM CFP transceivers can achieve long-distance data transmission in applications, when previously only SR4/LR4 options were available. It is an important feature enhancement to provide DWDM connectivity in a CFP transceiver for transporting 100G traffic over long distances. What’s more, coherent DWDM transceivers cost less than ER4 and ZR4 CFP transceivers. Now on the market, there are two types: CFP DCO (Digital Coherent Optic) and CFP2 ACO (Analog Coherent Optic).

CFP DCO has a high speed DSP (digital signal processing) chip built in which makes the coherent CFP a real workhorse. The DSP provides the electronic dispersion compensation and this eliminates the need of separate DCMs (dispersion compensation modules) of CFP. As a result, coherent CFP is able to support transmission distance of more than 1000km between sites.

The available CFP2 coherent DWDM transceivers are analog. Judging from the size, CFP2 ACO is half the width of CFP. Apart from this, another difference between CFP2 ACO and CFP is that CFP2 ACO does not has a DSP. In order to take the full advantages of the coherent features, CFP2 ACO requires a separate DSP on the host board. Though the DSP increases the power consumption and cost, it means that there is no need to add DSPs to the board.

PAM-4 100G DWDM Transceiver

PAM-4, adopted by the IEEE, is expected to be the most cost-effective and efficient enabler of 100G and beyond in the data center. PAM-4 makes more efficient use of electronic and optical components by packing two bits for every symbol sent over the fiber. Single-lambda 100G PAM-4 offers the simplest architecture, lowest component count, the most streamlined data path, higher reliability and an easy upgrade path to 400G Ethernet and beyond. And it enables the lowest-cost 100G transceiver. The 100G DWDM transceiver utilizes PAM-4 solution in QSFP28 form factor. For those who want to build an embedded DWDM network, they can use this transceiver directly in the switch. It is a very simple and cost-effective solution, but there is one tradeoff: it needs amplification to get out of the blocks and dispersion compensation to go beyond 5-6km. As a result, a separate DWDM multiplexer with an amplification system and dispersion compensation is required to connect data canters together. In addition, there is one thing to note: before the QSFP28 PAM-4 transceiver is added to an existing DWDM network, the network must prepare right DCM (dispersion compensation module) and amplification system in place.


Utilizing DWDM technology in the transceiver offers a simple and cost-effective solution. For coherent 100G DWDM transceiver, it is suitable for applications which needs longer reach; while for PAM-4 100G DWDM transceiver, it meets the needs of data center operators, such as Microsoft, that intend to turn up 4Tb/s of transmission capacity in a point-to-point fashion between data centers in a 70km metro-distributed network. Which one to choose depends on the specific deployment requirements.

Know More About 100GBASE-PSM4 QSFP28 Transceiver

There is an interesting phenomenon that multimode fibers are more expensive than single-mode fibers but the transceivers are the reverse. That is because the multimode core diameter is large and easy to align with VCSEL lasers and detectors while the single mode fiber cable is very hard to build and align transceiver components with and requires very expensive alignment equipment. Therefore, multi-mode transceivers are less expensive than single-mode transceivers. Now the 100G Ethernet network has been widely applied in data centers and there are various types of 100G fiber optic transceivers available on the market. Is there a type of 100G single-mode transceiver which can provide a low-cost solution for long-reach data center optical interconnects? The answer is Yes. The 100GBASE-PSM4 (parallel single-mode 4-lane) QSFP28 transceiver can do that.

Overview of 100GBASE-PSM4 QSFP28 Transceiver

The 100GBASE-PSM4 QSFP28 transceiver supports 100G link over eight single-mode fibers (four fibers for transmit and four fibers for receive) with data transmission distance up to 500 meters. It uses four parallel lanes for each signal direction and each lane carries 25G optical signal. In addition, the 100GBASE-PSM4 QSFP28 transceiver is structured with MTP/MPO interface, so it is usually used with single-mode fiber ribbon cable with MTP/MPO connector.

100GBASE-PSM4 QSFP28 transceiver
Working Principle of 100GBASE-PSM4 QSFP28 Transceiver

The figure below shows the working principle of the 100GBASE-PSM4 QSFP28 transceiver. The transmitter side accepts electrical input signals compatible with common mode logic (CML) levels, wile the receiver side converts parallel optical input signals via a photo detector array into parallel electrical output signals. The receiver module outputs electrical signals are also voltage compatible with CML levels. All data signals are differential and support a data rate up to 25Gbps per channel.

working principle of 100GBASE-PSM4 QSFP28 transceiver
Applications of 100GBASE-PSM4 QSFP28 Transceiver

The 100GBASE-PSM4 QSFP28 transceiver can be used for 100G to 100G connection. As the following figure shows, two 100GBASE-PSM4 QSFP28 transceivers are plugged into Host IC, then these two transceivers are connected by MTP/MPO patch cord and MTP/MPO patch panel.

100G to 100G connection with 100GBASE-PSM4 QSFP28 transceiver

From an optical transceiver module structure viewpoint, PSM uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. Therefore, the 100GBASE-PSM4 QSFP28 transceiver can be used for 100G to 4x25G connection. As the following figure shows, the 100GBASE-PSM4 QSFP28 transceiver and four 25G-LR SFP28 transceivers are connected by MTP-LC breakout cable.

100G to 4×25G connection with 100GBASE-PSM4 QSFP28 transceiver

The 100GBASE-PSM4 QSFP28 transceiver meets the requirement for low-cost 100G connections at reaches of 500 meters in applications that fall in between the IEEE multi-wavelength 10 kilometers 100GBASE-LR4 single-mode fiber approach and its multimode-fiber based 100GBASE-SR10 short reach specifications. It can support a link length of 500 meters over single mode fiber cable, which is sufficient for data center interconnect applications.

Cabling Solutions for 100G QSFP28 Transceiver

Since the demand for high speed data transmission keeps growing, 100G Ethernet has been widely deployed in data center. Designed for high port density with small compact size and low power consumption, 100G QSFP28 transceivers domain the 100G transceiver module market. There are four 100G QSFP28 transceiver types popular on the market—100GBASE-SR4 QSFP28 transceiver, 100GBASE-PSM4 QSFP28 transceiver, 100GBASE-CWDM4 QSFP28 transceiver and 100GBASE-LR4 QSFP28 transceiver. And in this article, I will share cabling solutions for 100G QSFP28 transceiver with you.

We know that the above four 100G QSFP28 transceiver types can be divided into two categories according to the interface: 100GBASE-SR4 QSFP28 and 100GBASE-PSM4 QSFP28 are with MTP/MPO interface, while 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28 are with duplex LC interface (shown as the figure below). Therefore, the cabling solutions are different respectively.

100G QSFP28 transceiver

Cabling Solution for 100G QSFP28 with MTP/MPO Interface

This kind of 100G QSFP28 transceiver is usually used with 100g MPO cable. For example, 100GBASE-SR4 QSFP28 can support 100G optical links over eight fibers and it can be connected with a 12-fiber MTP/MPO patch cable (four fibers for transmit, four fiber for receiver, leaving four fiber unused). Similar to 100GBASE-SR4 QSFP28, 100GBASE-PSM4 QSFP28 is also used with 12-fiber MTP/MPO patch cable. However, 100GBASE-SR4 QSFP28 utilizes multimode cable for 100 meters data transmission distance while 100GBASE-PSM4 QSFP28 utilizes single-mode cable for 500 meters optical links. Take 100GBASE-SR4 QSFP28 for example, the following figure shows that two 100GBASE-SR4 QSFP28 transceivers are connected with a multimode 12-fiber MTP trunk cable.

Cabling Solutions for 100GBASE-SR4 QSFP28 Transceiver

The following figure shows that with the use of multimode MTP-LC 8f fanout patch cord, one 100GBASE-SR4 QSFP28 transceiver can be connected with four 25GBASE-SR SFP28 transceivers.

100GBASE-SR4 with four 25GBASE-SR SFP28

Cabling Solution for 100G QSFP28 with Duplex LC Interface

Structured with duplex LC interface, 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28 are usually used with single-mode patch cables with LC duplex connectors. When upgrading the network, we often meet the problem that we have to replace all the fiber patch cables. However, you do not have to worry about this issue if your transceivers are 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28. Common single-mode duplex LC patch cable can meet the cabling requirement of these two transceivers. The following figure shows that two 100GBASE-CWDM4 QSFP28 transceivers are connected with a single-mode duplex LC patch cable.

Cabling Solutions for 100GBASE-CWDM4 QSFP28 Transceiver


For 100G QSFP28 with MTP/MPO interface, you can choose MTP/MPO cable, but remember that 100GBASE-SR4 QSFP28 utilizes multimode cable while 100GBASE-PSM4 QSFP28 utilizes single-mode cable; for 100G QSFP28 with duplex LC interface, you can use duplex LC patch cable for long distance transmission. I hope after reading this article, you can get something helpful.

Originally published at

Overview of 100G Transceivers

There was a time when 10G to 40G migration was a hot spot, and as the only available 40G transceiver, 40G QSFP+ has occupied the major position in the market. However, the pace of development has never stopped and the demand for higher speed data transmission keeps growing. And now, many data center managers set their sight on 100G Ethernet. As an important component in 100G optical links, 100G transceivers gradually gain great popularity among data center managers. But unlike 40G transceiver, 100G transceiver has several types, such as CFP/CFP2/CFP4, CXP and QSFP28. How much do you know about them? This article is going to give an overview of 100G transceivers.


The letter “C” in CFP/CFP2/CFP4 stands for 100. The CFP transceiver is specified by MSA between competing manufacturers and it can support 100Gbps over both single-mode and multimode fiber. The electrical connection of a CFP uses 10 x 10G lanes in each direction (RX, TX) while the optical connection can support both 10 x 10G and 4 x 25G variants of 100G interconnects. With improvement in higher performance and higher density, CFP2 and CFP4 appeared. While electrical similar, they specify a form factor of 1/2 and 1/4 respectively in size of CFP. CFP, CFP2 and CFP4 modules are not interchangeable, but would be inter-operable at the optical interface with appropriate connectors.


Here is a table for you which shows five typical transceiver types. We can get that CFP-SR10-100G is structured with 24-fiber MTP connector interface, so it can be used with multimode MTP 24 to MTP 24 100g trunk cable to support 100G optical links over short distance; designed with LC duplex interface, CFP-LR4-100G, CFP-ER4-100G, CFP2-LR4-100G and CFP4-LR4-100G are used with LC duplex patch cable to support 100Gbps data rate over long distance.

CFP CFP2 CFP4 transceiver information


The CXP was created to satisfy the high-density requirements of the data center, targeting parallel interconnections for 12x QDR InfiniBand (120G), 100G, and proprietary links between systems collocated in the same facility. The CXP is 45 mm in length and 27 mm in width, making it slightly larger than an XFP. It includes 12 transmit and 12 receive channels in its compact package. This is achieved via a connector configuration similar to that of the CFP.


Similar to 40G QSFP+, 100G QSFP28 also offers four independent transmit and receiver channels, but each channel is capable of 25Gbps data rate for an aggregate data rate for 100Gbps. With an upgraded electrical interface to support signaling up to 25Gbps signals, the 100G QSFP28 makes it as easy to deploy 100G network as 10G networks. When compared to any of the other alternatives, the 100G QSFP28 increases density and decreases power and price per bit, but It has to noted that 100G QSFP28 has the same physical size as 40G QSFP+. Just like 40G QSFP+, 100G QSFP28 can be both deployed for short data transmission distance over multimode fiber and long data transmission distance over single mode fiber. For example, 100GBASE-PSM4 QSFP28 can be used with MTP single mode cable to support 100G data rate with link length up to 500 meters.

100G QSFP28 transceiveres


Now is the time of 100G Ethernet and 100G transceivers are indispensable to complete the 100G optical links. As there are various types of 100G transceivers available on the market, it is necessary to choose the best suitable one for your network deployment.

Focus on 100G QSFP28 Transceiver

To satisfy the increasing demand for high speed data transmission, network technology has been developed rapidly, from Fast Ethernet, Gigabit Ethernet to 10G, 40G, and even 100G Ethernet. And we know that 40G network technology has been widely applied for a long time. But now, the time of 100G is coming. Though for many data centers, 40G is enough for them now, the pace of development is unpredictable. In addition, some data centers have been already migrated to 100G and a range of 100G fiber optic transceivers are available on the market, among which 100G QSFP28 transceivers are considered to be the preference choice. This article will focus on 100G QSFP28 transceiver and help you choose a suitable 100G QSFP28 transceiver for your network deployment. First, let’s come to the basic knowledge of four 100G QSFP28 transceiver types.

100GBASE-SR4 QSFP28 Transceiver

100GBASE-SR4 QSFP28 transceiver offers four independent full-duplex transmit and receiver channels, each capable of running up to 25Gpbs data rate per channel. Like 40GBASE-SR4 QSFP+ transceiver, 100GBASE-SR4 QSFP28 transceiver is structured with 12 fiber MPO connector interface and it can support 100G data transmission with link length up to 70 meters over OM3 and 100 meters over OM4.

100GBASE-PSM4 QSFP28 Transceiver

100GBASE-PSM4 is defined by MSA and it uses four independent parallel lanes for each signal direction, with each lane carrying 25G data transmission. Terminated with 12 fiber MPO connector interface, it can support 100G data transmission with link length up to 500 meters over single-mode fiber.

100GBASE-CWDM4 QSFP28 Transceiver

100GBASE-CWDM4 QSFP28 transceiver complies with the requirement of CWDM4 MSA. Based on CWDM technology, the 100GBASE-CWDM4 QSFP28 transceiver uses four lanes of 25Gbps. On the transmit side, the four 25G optical signals are multiplexed while on the receive side, the four 25G optical signals are de-multiplexed. Terminated with duplex LC interface, it can support 100G data transmission with link length up to 2 kilometers over single-mode fiber.

100GBASE-LR4 QSFP28 Transceiver

100GBASE-LR4 QSFP28 transceiver uses the WDM technologies for four 25G lanes transmission and the four 25G optical signals are being transmitted over four different wavelengths. Like 40GBASE-LR4 QSFP+ transceiver, the 100GBASE-LR4 QSFP28 transceiver has duplex LC interface and it can support 100G dual-way data transmission with link length up to 10 kilometers over single-mode fiber.

Which One to Choose?

From the above content, we can easily find that among four types of 100G QSFP28 transceivers, there are not only differences but also similarities. For example, 100GBASE-SR4 QSFP28 and 100GBASE-PSM4 QSFP28 are with MTP/MPO interface, while 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28 are with LC interface; 100GBASE-SR4 QSFP28 is suitable for for short distance over multimode fiber, while 100GBASE-PSM4 QSFP28, 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28 are suitable for long distance over single-mode fiber. Which one to choose depends on your specific requirements for network deployment. To better distinguish these four 100G QSFP28 transceiver types, here is a table for you.

four 100G QSFP28 transceiver types


100G QSFP28 transceiver is designed for high port density with small compact size and low power consumption. As 100G Ethernet is an inevitable trend, 100G QSFP28 transceiver is the key for 100G migration. Therefore, it is necessary to have a basic knowledge about 100G QSFP28 transceiver. Apart from this, before you carry out your network deployment, choosing a suitable transceiver is essential.

Originally published at