Coherent CFP2-ACO / CFP2-DCO WDM optical modules (100G / 200G) and their application in DWDM systems

The first press releases about the appearance of coherent CFP modules (coherent CFP optical pluggable modules) began to appear about 5-6 years ago. Then their use in optical sealing systems was new and was essentially a niche solution. Now, after six years, these modules have tightly entered the world of telecom and continue to gain popularity. What they are, how they differ and what solutions based on them offer (and of course the pictures under the spoilers) - all this under the cut. To read the article, you will need an understanding of the basic principles of DWDM systems.

A brief digression into the past

Historically, for optical pluggable modules with a transmission speed of 100G, the CFP form factor became the first form factor, it also became the first form factor for CFP-WDM solutions. At that time, there were two solutions on the market:

1. CFP from Menara (now part of IPG photonics) that allows transmitting 4 separate 28Gbps channels in a standard DWDM 50GHz frequency grid using pulse modulation. I did not get a strong distribution, although in principle I had an interesting potential for building metro networks. Further in the article we do not consider such modules.



2. CFP from the pioneers - Acacia press release , built on the most advanced at that time coherent detection technology using DP-QPSK modulation.




Such a module replaced the classic linear DWDM interface on a classic transponder operating in the C-band, which can be amplified, multiplexed, etc.

Now the principles of building coherent networks have become the de facto standard for building in the industry and this will not surprise anyone, and the density and range of optical compression systems has grown many times over.

Module components

Their first (Acacia) module was a type of CFP-ACO. A brief reference is given below on how the coherent CFP modules actually differ. But for this, you first need to make a small offtopic and tell a little about what DSP is, which is largely the heart of this technology.

So how do they differ?

Coherent optical modules are distinguished from each other by the location of the DSP:

• СFP-ACO - Only the optical part is located on the module. All electronics are located on the card (board; board) of the equipment where this module is inserted. At that time, there simply were no technologies to place the DSP inside the optical module. In fact, these are first-generation modules.
• CFP-DCO - in this case, the DSP is located in the optical module itself. The module is a complete “boxed solution”. These are second generation modules.

Externally, the modules have the exact same form factor. But they have different fillings, consumption (DCO is approximately twice as large) and heat generation. Accordingly, solution manufacturers have a certain flexibility - ACO gives a deeper integration of solutions, DCO allows you to get a solution "out of the box", using such an optical module as a lego cube to build your solution. A separate point - in the vast majority of cases, the work of a pair of DSP is possible exclusively from the same manufacturer. This imposes certain limitations and potentially makes DCO modules much more attractive for interopability tasks .

Solution Evolution

As progress does not stand still and MSA is constantly developing new standards, the last form factor in which DSP managed to be located is CFP2.


Form factor (CFP2) now prevails on all finished commercial products. You probably saw these connectors on telecom equipment and many are confused that these connectors are much more familiar to most QSFP28. Now you know one of the ways to use them (but it is better to make sure that the equipment can work with CFP2-ACO / DCO).


In addition to compact sizes, modulation methods are also being improved. In all CFP2-ACO / DCO products I know, not only DP-QPSK modulation is supported, but also QAM-8 / QAM-16. That is why these modules are called 100G / 200G. The customer himself can choose the modulation that suits him based on the tasks. In the near future, modules supporting speeds of up to 400G per optical channel should appear.


However, in the vast majority of cases, Ultra long haul (ULH) solutions use classic non-modular linear interfaces, which allow for greater range, better OSNR and higher modulation levels. Therefore, the main field of application of coherent modules are mainly merto / regional networks. If you look here , you can see that they probably

DSP Manufacturers

The global manufacturers of coherent DSPs that sell them to third-party companies are:

• Acacia
• Ciena
• INPHI
• NTT

Manufacturers CFP2-ACO / DCO

Manufacturers of coherent ACO / DCO modules:

• Acacia CFP2-ACO; CFP2-DCO; CFP-DCO
• Oclaro (at the time of writing, absorbed by Lumentum)
• Lumentum CFP2-ACO and CFP2-DCO
• NeoPhotonics CFP-DCO
• Finisar CFP2-ACO; CFP4-ACO
• Menara CFP2-DCO

Given that some of these companies are in a state of appraisal of the proposed mergers and acquisitions, it seems to me that the market for suppliers of such solutions will narrow. The production of such modules is a complex technological production, so for now I think it will not be possible to buy them from China suppliers for a long time.

Impact on the industry

The appearance of such modules has led to a small transformation of the ecosystem of the solutions offered on the market.

• At first

Manufacturers began to use them in classic (transponder) DWDM solutions, as conventional linear interfaces. Having received a bonus modularity, flexibility and cost reduction (by the way, such solutions are often chosen as Alien Wavelength).

For instance:

• BTI UFM6 (Juniper)
• Packetlight PL2000xx
• Coriant Groove G30 (Infinera)
• Huawei TN18LSC
• Ciena 5430
• Fujitsu 1FINITY

• Secondly

manufacturers already supplying telecom equipment - switches and routers, expanded the range and added support for such modules, further bringing us closer to the so-called IPoDWDM systems . For instance:

• Juniper (MX / QFX / ACX)
• Cisco (NCS / ASR)
• Nokia (SR)
• Arista (7500R)
• Edge-Core (Cassini AS7716-24SC)

All of the manufacturers listed in the equipment line already have boards for routers or switches that support coherent CFP2 modules.

• Separately

It is worth mentioning interesting trends in the global community, for example, the TIP project, one of the focuses of which is the development of open optical networks . The construction of such networks will allow integrating equipment into open source control systems, making the interaction between manufacturers of optical systems more transparent and open. In addition, on the devices themselves (both on transponders using DCO modules, and on ROADM / EDFA), it is planned to use software from various suppliers (for example, Ipinfusion ). Therefore, the trend of recent years remains the unification of the component base of solutions and the uniqueness of software development, in which a fairly large stake has been made on opensource.

Thank you for your attention, I hope this article turned out to be interesting and useful to you. You can ask additional questions in the comments or in person. If you have something to add on this topic, I will be very happy.