Coherent CFP WDM (100G / 200G) and their application in DWDM systems

The first press releases about the emergence 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 firmly entered the world of telecom and continue to gain popularity. What they are, how they differ and what solutions based on their offer (and of course the pictures under the spoilers) - all this is under the cut. To read the article you will need an understanding of the basic principles of DWDM systems.

A brief excursion into the past

Historically, for optical pluggable modules with a transfer rate of 100G, the CFP form factor was the first, and 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 the IPG photonics) allows you to send 4 separate 28Gbps channels to the line in a standard DWDM 50GHz frequency grid using pulse modulation. Not widely spread, although in principle it had an interesting potential for building metro networks. Further in the article we do not consider such modules.
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2. CFP from the pioneers - Acacia press release , built on the most advanced at the time of coherent detection technology using DP-QPSK modulation.




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

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

Module components

Their first (Acacia) module was a CFP-ACO type. Below is a brief reference to the actual differences between coherent CFP modules. But for this, you first need to make a small offtopic and tell a little about what DSP is, which is in many ways the heart of this technology.

So how are they different?

Coherent optical modules distinguish each other from the DSP layout:

• FP-ACO - Only the optical part is located on the module. All electronics are located on the board (card; board) of the equipment where this module is inserted. At that time, there simply wasn’t any technology to accommodate 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 a completely identical form factor. But they have different fillings, consumption (DCO is approximately twice as large) and heat generation. Accordingly, decision makers have a certain flexibility - ACO provides deeper integration of solutions, DCO allows you to get a solution out of the box, using such an optical module as a cube Lego to build your solution. A separate moment - in the overwhelming majority of cases, the work of a pair of DSPs is possible exclusively for the same manufacturer. This imposes certain limitations and potentially makes DCO modules much more attractive for interopability tasks .

Evolution of the solution

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


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


In addition to compact size, modulation methods are also being improved. In all CFP2-ACO / DCO products known to me, not only DP-QPSK modulation is supported, but also QAM-8 / QAM-16. That is why these modules are called 100G / 200G. The customer 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 overwhelming majority of cases for Ultra long haul (ULH) solutions classic non-modular linear interfaces are used, which allow for longer range, better OSNR and higher modulation levels. Therefore, the main area of ​​application for coherent modules is mainly merto / regional networks. If you look here , you can see that they probably

DSP manufacturers

The global coherent DSP manufacturers who sell them to third-party companies are:

• Acacia
• Ciena
• INPHI
• NTT

CFP2-ACO / DCO Manufacturers

Manufacturers of ACO / DCO coherent modules:

• Acacia CFP2-ACO; CFP2-DCO; CFP-DCO
• Oclaro (at the time of writing, absorbed 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 and proposed mergers and acquisitions, the market for suppliers of such solutions, it seems to me, will narrow. The production of such modules is a complicated technological production, so for now, I think it will not be possible to buy them from the suppliers of the Middle Kingdom for a long time.

Impact on the industry

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

• First of all

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

For example:

• 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 example:

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

All of the listed manufacturers 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 is 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 optical system manufacturers 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 vendors (for example, Ipinfusion ). Therefore, the trend of recent years is the unification of the component base of solutions and the uniqueness of software development, in which a sufficiently large bet is made on the opensource.

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