Co-Packaged Optics to play an important role in data center switches

The commercialization of co-packaged optics (CPO) has been long anticipated but is becoming increasingly desirable as data needs accelerate. Co-Packaged Optics are an advanced heterogeneous integration of optics and silicon on a single packaged substrate aimed at addressing next generation bandwidth and power challenges.

As the bandwidth of data center switches increases, a disproportionate amount of power is becoming dedicated to the switch – optics interface. Reducing the physical separation between these two components by co-packaging enables system power savings which is essential to continued bandwidth scaling.

CPO brings together a wide range of expertise in fiber optics, digital signal processing (DSP), switch ASICs, and state-of-the-art packaging and test to provide disruptive system value for the data center and cloud infrastructure.

The companies and institutions working on CPO have made great strides in developing suitable electronic components. But hundreds of meters of fiber will be packed into the switch box for the first time, and faceplate connections will have unprecedented densities. As a result, the design and development of optical system solutions will also be critical elements in the success of CPO.  Optical components with performance tailored to the CPO application and effective solutions for managing the fiber in the switch box are vital in optimizing the complete optical system. Three aspects of CPO deployment, in particular, hinge on the properties of the fiber and the optical interfaces: optical power loss, the trade-off between minimizing bend loss and controlling for MPI and maintaining the polarization state if external lasers are used.

Image Courtesy of Broadcom


Data centers face substantial challenges as they scale, particularly in reducing power dissipation and cost per bit. CPO will play a significant role in helping to meet those challenges.  In today’s data center switches, external fiber optic connections that carry data terminate on pluggable transceivers on the housing faceplate. The optical data stream is coupled to the electrical signals at that interface.

With a CPO realization of a 51.2 Tbps switch, the substrate connects a central regulator ASIC to 16 optoelectronic (O/E) tiles on the substrate perimeter. These tiles are connected to optical fiber signal cables that run to the switch box faceplate and receive power from external lasers that they modulate to produce the outgoing optical signal stream.

They communicate between the transceiver and the switch application-specific integrated circuit (ASIC) via copper traces on printed circuit boards. Under the CPO paradigm, as the optoelectronic conversion is pushed back from the faceplate to the switch substrate, long electrical traces are replaced with virtually loss-free optical fiber.

With CPO, the fiber path continues past a connector at the faceplate and into the switch box, ending at photonic integrated circuits (PICs) on optical tiles attached to the switch substrate. This shift presents the novel challenge of routing and connecting hundreds of optical fibers within a compact and crowded space, creating a need to minimize the footprint of the optics while still achieving performance and reliability targets.

CPO will soon be a reality that relies on a system of complex, interconnected components working well together. For optimum overall performance, these components must be designed with the specific requirements of CPO in mind, which for the optical subsystem include efficient and unobtrusive deployment within a crowded switch box, low power losses, absence of MPI impairments, and good reliability. Some CPO realizations also need optical polarization state control.

The familiar fiber and connectivity products, while having impressive attributes, are not optimum for the CPO application, and there is great scope for enhancing the performance of the optics by moving beyond default solutions to those specifically designed for the role.

Minimizing the optics footprint could mean routing fiber on the shortest path – consistent with the fiber properties – between the optical tile and its associated faceplate connector, but this would lead to at least eight different cable lengths for a 51.2 Tbps switch with 16 optical tiles and mirror symmetry. This proliferation of parts might be undesirable from a manufacturing point of view. If a reduced set of cable lengths were to be used, then the “constant length” routing would have to accommodate excess cable in some paths.

Image Courtesy of LightWave 


With space inside the switch box at a premium, the risk of mechanical interference with other components should be reduced as much as possible. When building switch boxes containing hundreds of fibers, it will be essential to have them deployed predictably while minimizing trouble spots like crossings and avoiding issues such as cable buckling.

This management goal will be greatly facilitated by using tightly bent fiber to follow short paths between the faceplate and chip. With typical telecommunications-grade single-mode fiber, too much light may be lost at these bends, but we can mitigate this by using bend-insensitive fiber designs.  However, in using such designs, care will be required to control multipath interference (MPI).

Power can be coupled and propagated in more than one fiber mode at each optical interface in the switch box (e.g., connectors, FAUs). Given the short fiber lengths likely to be used in CPO, power in higher-order modes (HOMs) will not be extinguished before the following interface, where the multiple modes will interfere with each other – the phenomenon known as MPI – ultimately causing wavelength-dependent power at the detector. At some wavelengths, that power reduction could be up to twice in decibels, arising from the independent losses at each interface.

Thus, unmitigated MPI could complicate some benefits of using fiber with low bend-loss. For these systems, a bend-insensitive fiber that also suppresses MPI in very short fiber lengths would need to be designed. One potential approach is to reduce the fiber cut-off wavelength to increase HOM loss substantially.

Even if MPI is reduced to insignificance, the coupling losses at those interfaces matter, too. The redesigned bend-insensitive fiber must maintain low coupling loss to Corning® SMF-28® Ultra or other fiber used in the data center to connect switches. This imposes constraints on the mode-field diameter of the CPO signal fiber.

To permit practical, low-cost provisioning of the switch box optical cables, the fiber management approach must include some means to accommodate length variations introduced by the cable manufacturing process. One strategy is to tie down the cable at points along its path and allow it to take a relatively unconstrained path between these tie-down points. The smaller the radius of curvature of that path, the less a bundle of cables will spread out for a given length variation.

An alternative is to provide specific accumulator structures to contain excess cable length. To keep such structures unobtrusive, the fiber should tolerate deployment in very tight loops, as small as 10-mm in diameter, retaining its low-bend loss and high reliability. These attributes are required of fiber that lends itself to “shortest path” and “constant length” routing.


CPO will soon be a reality that relies on a system of complex, interconnected components working well together. For optimum overall performance, these components must be designed with the specific requirements of CPO in mind, which for the optical subsystem include efficient and unobtrusive deployment within a crowded switch box, low power losses, absence of MPI impairments, and good reliability. Some CPO realizations also need optical polarization state control.

The familiar fiber and connectivity products, while having impressive attributes, are not optimum for the CPO application, and there is great scope for enhancing the performance of the optics by moving beyond default solutions to those specifically designed for the role.


Coherent Optics: Synergistic for telecom, Data Center Interconnect (DCI) and inter-satellite Networks

Heavy Reading: Coherent Optics for 400G transport and 100G metro edge

Broadcom, Cisco and Facebook Launch TIP Group for open source software on 6 GHz Wi-Fi

The Telecom Infra Project (TIP) has formed a new group to speed the introduction of commercial Wi-Fi devices for the 6 GHz band. Broadcom, Cisco and Facebook are leading the creation of the Open Automated Frequency Coordination (Open AFC) Software Group.

The purpose of this new TIP project group is to develop a common reference open source software for an AFC system. The AFC will be used by unlicensed devices in the newly available 6 GHz band to operate outdoor and increased range indoor while ensuring incumbent services are protected.

The US, EU, Canada, and Brazil, among others, have approved or are finalizing the approval of 6 GHz unlicensed spectrum use, opening up a huge bandwidth for Wi-Fi services.

By 2025, the Wi-Fi Alliance estimates that the 6 GHz Wi-Fi will deliver USD 527.5 billion in incremental economic benefits to the global economy [1]. Standard outdoor power operations will be a key part of the value proposition of 6 GHz Wi-Fi and is critical for enabling more affordable wireless broadband for consumer access.

The FCC is the first regulator to enable its use under an AFC, ISED Canada authorized standard power with AFC in May 2021, with others expected to follow. The AFC will enhance Wi-Fi to provide a consistent wireless broadband user experience in stadiums, homes, enterprises, schools, and hospitals.

“The 6 GHz Wi-Fi momentum is unmistakable. In the year following the historic FCC ruling to open up the band for unlicensed access, we already have an entire ecosystem of Wi-Fi 6E devices delivering gigabit speeds indoors. As we work towards closing the digital divide and further realizing the value of the 6 GHz band, AFC-enabled standard power Wi-Fi operation becomes critical. As Wi-Fi 7 comes along, AFC will turbocharge the user experience by enabling over 60 times more power for reliable, low latency, and multi-gigabit wireless broadband both indoors and outdoors. With this vision in mind, Broadcom is excited to join hands with Cisco and Facebook to create the TIP Open AFC Software Group aimed at enabling a cost effective and scalable AFC system,” said Vijay Nagarajan, Vice President of Marketing, Wireless Communications & Connectivity Division, Broadcom.

“The creation of the TIP Open AFC Software Group represents the immense momentum behind unlicensed spectrum and the potential it holds to deliver innovation,” said Rakesh Thaker, VP of Wireless Engineering, Cisco. “Many of the applications and use cases we’re just beginning to dream up with the introduction of Wi-Fi 6 and the 6 GHz spectrum will rely on standard power, greater range and reliability. This software group will play an important role in ensuring those applications can become reality, while also protecting important incumbent services. We’re thrilled to join Broadcom and Facebook on this effort, and to share a vision with TIP of providing high-quality, reliable connectivity for all.”

Facebook developed a proof of concept Open AFC system, which will protect 6 GHz incumbent operations and enable faster adoption of standard power operations in the 6 GHz band. This prototype system will be contributed to the TIP community through today’s launch of the Open AFC Software Group, with the goal of enabling the proliferation of standard power devices in the United States to start, with other markets to follow.

Broadcom and Cisco have committed to driving the industry forward in developing Open AFC to ensure that the code continues to be developed to meet the needs of the industry and regulators, such that an AFC operator could take the code and build upon it for rapid certification.

The vast majority of Wi-Fi use is indoors, but there are situations where people will want to use Wi-Fi outdoors. The use of AFC provides the flexibility for outdoor deployments in open air stadiums and similar venues.

“Bringing AFC technology to the TIP Open AFC Software Group is a huge milestone for the unlicensed spectrum community,” said Dan Rabinovitsj, vice president for Facebook Connectivity. “We are excited to see the contributions and innovations by Open AFC and we look forward to celebrating the widespread adoption of the 6 GHz band, which will rapidly accelerate the performance and bandwidth of Wi-Fi networks around the world”.

David Hutton, Chief Engineer of TIP, said: “The industry is coming together to support 6 GHz for unlicensed use for Wi-Fi and TIP will be providing the forum to contribute to make this happen, supporting regulatory efforts by ensuring that AFC systems are developed under a common code base that is available to all industry stakeholders.”

Closing Comment:

We wonder why this new WiFi 6GHz group is in TIP rather than the WiFi Alliance.  From the WiFi Alliance Certified 6:

“Wi-Fi Alliance is leading the development of specifications and test plans that can help ensure that standard power Wi-Fi devices operate in 6 GHz spectrum under favorable conditions, avoiding interference with incumbent devices.”

In this author’s opinion, there are way too many alliances/ fora/ consortiums that produce specifications that are to be used with existing standards.  In this case (IEEE 802.11ax) there is potential overlap amongst amongst groups, which leads to inconsistent implementations that inhibit interoperability.


Nokia and Broadcom collaborate on new 5G ReefShark SoC’s

Nokia and Broadcom said today that they are cooperating to develop advanced system-on-chip (SoC) processors, for integration with Nokia’s 5G Powered by ReefShark portfolio. The new SoC products use Nokia wireless technology and Broadcom expertise in application-specific integrated circuit (ASIC) technologies.

The added performance brought by custom silicon solutions is crucial in realizing the capabilities and benefits of 5G and delivering on its requirements. This new alliance extends the range of Nokia ReefShark chipsets available for 5G networks and improves the performance and energy footprint of 5G networks. While collaborating with Broadcom, Nokia continues to expand its silicon capabilities and improve the penetration of Reef Shark products in its AirScale radio access network (RAN) portfolio.

Nokia, Broadcom Collaborate to Develop New Custom SoC Processors

ReefShark is based on 3GPP (Release 15) 5G New Radio specifications, which help offset deployment costs and TCO, while fulfilling architecture-driven network requirements.

ReefShark reduces size, cost and energy consumption at each cell site, while simultaneously boosting the intelligence and performance of massive MIMO antennas.

ReefShark boosts baseband compute capacity through plug-in units fitted into the commercially available Nokia AirScale system module. AirScale is software upgradeable to full 5G functionality, and these plug-in units triple throughput from Nokia’s already market-leading 28 Gbps today, to up to 85 Gbps per module.


The new chipsets are designed for deployment in several building blocks of Nokia’s AirScale radio access system. Reef Shark-based items enable operators to benefit from a smaller size and power consumption but a boost in capacity and overall performance, with a lower total cost of ownership.

Tommi Uitto, President of Mobile Networks, Nokia:

“This important collaboration highlights our continued commitment to developing our “5G Powered by ReefShark” chipset portfolio and ensures that our 5G solutions deliver a best-in-class performance to our customers.”

Frank Ostojic, SVP and GM, ASIC Products Division, Broadcom:

“Nokia and Broadcom’s collaboration accelerates silicon innovation and enables operators and end users to realize the unprecedented benefits of 5G.”


About Broadcom
Broadcom Inc. (NASDAQ: AVGO) is a global technology leader that designs, develops and supplies a broad range of semiconductor and infrastructure software solutions. Broadcom’s category-leading product portfolio serves critical markets including data center, networking, enterprise software, broadband, wireless, storage and industrial. Our solutions include data center networking and storage, enterprise, mainframe and cyber security software focused on automation, monitoring and security, smartphone components, telecoms and factory automation. For more information, go to

About Nokia
We create the technology to connect the world. Only Nokia offers a comprehensive portfolio of network equipment, software, services and licensing opportunities across the globe. With our commitment to innovation, driven by the award-winning Nokia Bell Labs, we are a leader in the development and deployment of 5G networks.

Our communications service provider customers support more than 6.4 billion subscriptions with our radio networks, and our enterprise customers have deployed over 1,300 industrial networks worldwide. Adhering to the highest ethical standards, we transform how people live, work and communicate. For our latest updates, please visit us online and follow us on Twitter @nokia.

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