OFC 2024 industry reflections: Part 4
Gazettabyte is asking industry figures for their thoughts after attending the recent OFC show in San Diego. This penultimate part includes the thoughts of Cisco’s Ron Horan, Coherent’s Dr. Sanjai Parthasarathi, and Adtran’s Jörg-Peter Elbers.
Ron Horan, Vice President Product Management, Client Optics Group, Cisco
Several years ago, no one could have predicted how extensive the network infrastructure required to support artificial intelligence (AI) and machine learning (ML) back-end networks in data centres would be. This year’s OFC answered that question. In a word, immense.
By 2025, the optics total addressable market for AI/ML back-end networks is expected to equal the already substantial front-end network optics market. By 2027, the back-end network optics total addressable market is projected to significantly exceed that of the front-end network. Additionally, the adoption of higher speeds and interface densities in the AI/ML back-end network will likely surpass that of the front-end.
Last year, linear pluggable optics (LPO) advocates heralded the power and cost savings associated with removing the digital signal processor (DSP) from an optics module and driving it directly from the host ASIC. Cisco and others have shown, using data and demos, that the overall power and cost savings are significant. However, in the last year, enthusiasm for this disruptive technology has been checked as concerns about link robustness and accountability have surfaced.
Enter linear receive optics (LRO), where the transmit path gets retimed while the high-power module receiver path moves to a linear receiver, which drives directly to the host ASIC. While not as power or cost friendly as linear pluggable optics, it does reduce power and some cost from the module compared to a fully retimed module while providing some diagnostic support for the link.
Only time and significant interoperability testing will determine whether linear pluggable optics or linear receive links will be robust enough to make them deployable at scale. Additionally, today’s linear pluggable and linear receive solutions have only been shown at 100 gigabits per lane. It is unclear whether 200 gigabits per lane for both approaches can work. Many think not. If not, then 100 gigabit per lane linear pluggable and linear receive optics may be a one-generation technology that is never optimal. The LPO-MSA, an industry effort that included many of the industry’s key companies, was announced before OFC to specify and resolve interoperability and link accountability concerns.
The overall concern about reducing power in the data centre was a strong theme at the show. The linear pluggable optics/ linear receive optics theme was born from this concern. As optics, switches, routers, and GPU servers become faster and denser, data centres cannot support the insatiable need for more power.
However, end users and equipment manufacturers seek alternative ways to lower power, such as liquid cooling and immersion. Liquid cooling uses liquid-filled pipes to remove the heat, which can help cool the optics. Liquid immersion further amplifies the cooling approach by immersing the optics, along with the host switch or GPU server, directly into an inert cooling fluid or placing them just above the fluid in the vapour layer. The ultimate result is to operate the optics at a lower case temperature and save power. It seems each customer is approaching this problem differently.
Last year’s OFC produced the first optics with 200 gigabit per optical lane technology. These solutions assumed a gearbox to a host interface that used 100-gigabit electrical channels. While some early adopters will use systems and optics with this configuration, a more optimal solution using 200 gigabits per lane electrical channels between the host and optics will likely be where we see 200 gigabits per lane optics hit their stride. This year’s show revealed a broader set of optics at 200 gigabit per lane rates. The technology maturity was markedly improved from last year’s early feasibility demos.
This is an exciting time in the optics industry. I look forward to learning what technologies will be introduced at OFC 2025.
Dr. Sanjai Parthasarathi, Chief Marketing Officer, Coherent
The progress in making 200-gigabit VCSELs ready for 200-gigabit PAM-4 optical transmission was a pleasant surprise of the event.
We at Coherent presented a paper on our lithographic aperture VCSEL, while Broadcom’s presentation outlined the technical feasibility of 200-gigabit PAM4 links. While both mentioned that more work is needed, the historic success of VCSEL-based links in short-reach interconnects suggests that the arrival of 200G-capable VCSELs will significantly impact the datacom market.
The feasibility of linear pluggable optics has likely delayed the market acceptance of co-packaged optics. There seems to be widespread consensus that LPO can reduce cost and power while retaining all the advantages of pluggable transceivers – a vibrant ecosystem, deployment flexibility, and a clear distinction of link accountability.
Jörg-Peter Elbers, senior vice president, advanced technology, standards and IPR, Adtran.
At this year’s OFC, discussions were much hotter than the weather. Who would have anticipated rain, winds and chilly temperatures in an always-sunny San Diego?
AI infrastructure created the most buzz at OFC. Accelerated compute clusters for generative AI are expected to drive massive demands for high-speed interconnects inside cloud-scale data centres. Consequently, 800-gigabit, 1.6-terabit, and future 3.2-terabit pluggable optical transceivers for front-end and back-end data centre fabrics stirred a lot of interest. Progress on co-packaged optics was also exciting, yet the technology will only go into deployments where and when pluggable transceivers hit unsurmountable challenges.
Silicon Photonics, indium phosphide, thin-film lithium niobate and VCSEL-based optics compete for design slots in a very competitive intra-data centre market, leading to new partnerships across the pluggable transceiver value chain. Linear receive optics and linear transmit & receive pluggable optics offer opportunities to reduce or eliminate DSP functions where electrical signal integrity permits.
While green ICT (information and communications technology) received a lot of attention at the conference, comments at the OFC Rump Session on this topic were somewhat disenchanting: time-to-market and total-cost-of-ownership drive deployment decisions at hyperscale data centres; lower energy consumption of optics is welcome but not a sufficient driver for architectural change.
On the inter-data centre side, a range of companies announced or demonstrated 800G-ZR/ZR+ transceivers at the show. More surprising was the number of transceiver vendors – including those not traditionally active in this market domain – who have added 400G-ZR QSFP-DD transceivers to their product portfolio. This indicates that the prices of these transceivers may decline faster than anticipated.
As for the next generation, industry consensus is building up behind a single-wavelength 1.6T ZR/ZR+ ecosystem using a symbol rate of some 240 gigabaud. There was a period in which indium phosphide and silicon photonics seemed to have taken over, and LiNbO3 appeared old-fashioned. With the move to higher symbol rates, LiNbO3 – in the form of thin-film Lithium Niobate – is celebrating a comeback: “Lithium Niobate is dead – long live Lithium Niobate!”
The OIF’s largest ever interop demo impressively showed how 400G-ZR+ modules can seamlessly interoperate over long-haul distances using an open-line system optimized for best performance and user-friendly operation. Monitoring and controlling such pluggable modules in IPoWDM scenarios can create operational and organizational challenges and is the subject of ongoing debates in IETF, TIP and OIF. A lean demarcation unit device can be a pragmatic solution to overcome these challenges in the near term. In the access/aggregation domain, the interest in energy-efficient 100G-ZR solutions keeps growing.
As the related OFC workshop showed, growing is also the support for a coherent single-carrier PON solution as the next step in the PON roadmap after 50Gbps very high-speed PON (VHSP).
Overall, there was excitement and momentum at OFC, with the conference and show floor returning to pre-Covid levels.
This is a good basis for the 50th anniversary edition of ECOC, taking place in Frankfurt, Germany, on September 22-26, 2024.
ECOC '22 Reflections - Final Part
Gazettabyte has been asking industry and academic figures for their thoughts after attending ECOC 2022, held last month in Basel, Switzerland. In particular, what developments and trends they noted, what they learned, and what, if anything, surprised them.
In the final part, Dr. Sanjai Parthasarathi of Coherent, Acacia’s Tom Williams, ADVA’s Jörg-Peter Elbers and Fabio Pittalà of Keysight Technologies share their thoughts.
Dr. Sanjai Parthasarathi, Chief Marketing Officer, Coherent
The ECOC event represents an excellent opportunity for us – a vertically-integrated manufacturer selling at all levels of the value chain – to meet with customers, end-customers and partners/ suppliers.
There was a refreshing sense of optimism and excitement for optical communications, driven by relentless bandwidth growth, despite the macroeconomic backdrop.
The roadmap for optical transceivers is dictated by the electrical interface used for Ethernet switch chips. We have seen that play out yet again for 100-gigabit electrical lanes used for 25-terabit and 50-terabit Ethernet switches.
Several transceiver suppliers demonstrated products with 100 gigabit-per-lane electrical interfaces in quad and octal form factors. The optical lane of a transceiver typically begins at the same speed as the electrical lane and then progresses to a faster rate. This transition should be expected for 800-gigabit transceivers as well.
While 100 gigabit-per-lane transceivers, such as the 800G-DR8 and the 2x400G-FR4 devices, there were devices demonstrated that enable the transition to optical 200-gigabit lanes. It was satisfying to see a warm response for the demonstration of Coherent’s 200-gigabit electro-absorption modulated laser (EML) and Semtech’s 200-gigabit EML driver. I am confident that direct detection will play a predominant role in 800-gigabit and 1.6-terabit data centre links.
Despite the great interest in co-packaged optics, nearly all the working demonstrations at the show used pluggable transceiver modules. Industry colleagues are preparing for pluggable transceiver modules using the next 200-gigabit electrical interface. Indeed, at ECOC, there was an OIF-CEI 224G demo by Keysight and Synopsys.
One key topic at the show concerned whether ‘coherent lite’ or direct detect is the preferred solution for data centres and edge aggregation. The debate remains open and no one solution fits all. It will depend on the specific application and architecture. A broad portfolio supported by different technology platforms frees you to select the best approach to serve the customer’s needs.
I saw the industry responding to the need for disaggregation and innovative solutions for access and telecom. Coherent’s 100G ZR announcement is one such example, as well as the extra performance of high-power 400ZR+ coherent transceivers.
We started this trend and we now see others announcing similar solutions.
Arista’s demo, which featured 400ZR connections over a 120km data centre interconnect (DCI) link, enabled by our pluggable optical line system in a QSFP form factor, received much attention and interest.
Tom Williams, Senior Director of Marketing for Acacia, now part of Cisco.
Many of us are still of a mindset where any opportunity to get together and see industry friends and colleagues is a great show.
My focus is very much on the success of 400-gigabit pluggable coherent solutions.
We’ve been talking about these products for a long time, back to the initial OIF 400ZR project starting in late 2016. Since then, 400ZR/ZR+ has been a hot topic at every conference.
The commercial success of these solutions, and the impact that they’re having on network architectures, has been gratifying. These products have ramped in volumes not seen by any previous coherent technology.
The industry has done a great job at 400 gigabits, striking the right balance of power and performance. Now, we’re looking at 800 gigabits and working through some of the same questions. Discussions around 1.6 terabits have even started.
Much work is still required but what we heard from customers at ECOC is that the trend toward pluggable coherent will likely continue.
Jörg-Peter Elbers, Senior Vice President, Advanced Technology, Standards and IPR at ADVA
‘Never say never’ captures well ECOC’s content. There was no one groundbreaking idea but topics discussed in the past are back on the agenda, either because of a need or the technology has progressed.
Here are several of my ECOC takeaways:
- The 130 gigabaud (GBd) class of coherent optics is coming, and the generation after that – 240GBd – is on the horizon.
- Coherent optics continue to push towards the edge. Will there be a Very-High Speed Coherent PON after 50G High-Speed PON?
- Whether co-packaged optics or front-pluggable modules, electro-photonic integration is rapidly advancing with some interesting industry insights shared at the conference.
- Quantum-safe communication is becoming part of the regular conference program.
- Optical Satcom is gaining traction. Optical ground-to-space links are promising yet challenging.
Fabio Pittalà, Product Planner, Broadband and Photonics – Center of Excellence, Keysight Technologies
This was my first ECOC as an employee of Keysight. I spent most of my time at the exhibition introducing the new high-speed Keysight M8199B Arbitrary Waveform Generator.
There were a lot of discussions focusing on technologies enabling the next Ethernet rates. There is a debate about intensity-modulation direct detection (IMDD) versus coherent but also what modulation format, symbol rate or degree of parallelisation.
While the industry is figuring out the best solution, researchers achieved important milestones by transmitting the highest symbol rate and the highest net bitrate.
Nokia Bell-Labs demonstrated record-breaking transmission of 260-gigabaud dual-polarisation quadrature phase-shift keying (DP-QPSK) over 100km single-mode fibre.
Meanwhile, NTT broke the net bitrate record by transmitting more than 2 terabit-per-second using a probabilistic-constellation-shaped dual-polarisation quadrature amplitude modulation (DP-QAM) over different data centre links.
II-VI expands its 400G and 800G transceiver portfolio
II-VI has showcased its latest high-speed optics. The need for such client-side modules is being driven by the emergence of next-generation Ethernet switches in the data centre.
The demonstrations, part of the OFC virtual conference and exhibition held last month, featured two 800-gigabit and two 400-gigabit optical transceivers.
“We have seen the mushrooming of a lot of datacom transceiver companies, primarily from China, and some have grown pretty big,” says Sanjai Parthasarathi, chief marketing officer at II-VI.
But a key enabler for next-generation modules is the laser. “Very few companies have these leading laser platforms – whether indium phosphide or gallium arsenide, we have all of that,” says Parthasarathi.
During OFC, II-VI also announced the sampling of a 100-gigabit directly modulated laser (DML) and detailed an optical channel monitoring platform.
“We have combined the optical channel monitoring – the channel presence monitoring, the channel performance monitoring – and the OTDR into a single integrated subsystem, essentially a disaggregated monitoring system,” says Parthasarathi.
An optical time-domain reflectometer (OTDR) is used to characterise fibre.
High-speed client-side transceivers
II-VI demonstrated two 800-gigabit datacom products.
One is an OSFP form factor implementing 800-gigabit DR8 (800G-DR8) and the other is a QSFP-DD800 module with dual 400-gigabit FR4s (2x400G-FR4). The DR8 uses eight fibres in each direction, each carrying a 100-gigabit signal. The QSFP-DD800 supports two FR4s, each carrying four, 100-gigabit wavelengths over single-mode fibre.
“These are standard IEEE-compliant reaches: 500m for the DR8 and 2km for the dual FR4 talking to individual FR4s,” says Vipul Bhatt, senior strategic marketing director, datacom at II-VI.
The 800G-DR8 module can be used as an 800-gigabit link or, when broken out, as two 400-gigabit DR4s or eight individual 100-gigabit DR optics.
II-VI chose to implement these two 800-gigabit interfaces based on the large-scale data centre players’ requirements. The latest switches use 25.6-terabit Ethernet chips that have 100-gigabit electrical interfaces while next-generation 51.2-terabit ICs are not far off. “Our optics is just keeping in phase with that rollout,” says Bhatt.
During OFC, II-VI also showcased two 400-gigabit QSFP112 modules: a 400-gigabit FR4 (400G-FR4) and a multi-mode 400-gigabit SR4 (400G-SR4).
The SR4 consumes less power, is more cost-effective but has a shorter reach. “Not all large volume deployments of data centres are necessarily in huge campuses,” says Bhatt.
II-VI demonstrated its 800-gigabit dual FR4 module talking to two of its QSFP112 400-gigabit FR4s.
Bhatt says the IEEE 802.3db standard has two 400G-SR4 variants, one with a 50m reach and the second, a 100m reach. “We chose to demonstrate 100m because it is inclusive of the 50m capability,” says Bhatt.
II-VI stresses its breadth in supporting multi-mode, short-reach single-mode and medium-reach single-mode technologies.
The company says it was the electrical interface rather than the optics that was more challenging in developing its latest 400- and 800-gigabit modules.
The company has 100-gigabit multi-mode VCSELs, single-mode lasers, and optical assembly and packaging. “It was the maturity of the electrical interface [that was the challenge], for which we depend on other sources,” says Bhatt.
100-gigabit PAM-4 DML
II-VI revealed it is sampling a 100-gigabit PAM-4 directly modulated laser (DML).
Traditionally, client-side modules for the data centre come to market using a higher performance indium phosphide externally-modulated laser (EML). The EML may even undergo a design iteration before a same-speed indium phosphide DML emerges. The DML has simpler drive and control circuitry, is cheaper and has a lower power consumption.
“But as we go to higher speeds, I suspect we are going to see both [laser types] coexist, depending on the customer’s choice of worst-case dispersion and power tolerance,” says Bhatt. It is too early to say how the DML will rank with the various worst-case test specifications.
Parthasarathi adds that II-VI is developing 100-gigabit and 200-gigabit-per-lane laser designs. Indeed, the company had an OFC post-deadline paper detailing work on a 200-gigabit PAM-4 DML.
Optical monitoring system
Optical channel monitoring is commonly embedded in systems while coherent transceivers also provide performance metrics on the status of the optical network. So why has II-VI developed a standalone optical monitoring platform?
What optical channel monitors and coherent modules don’t reveal is when a connector is going bad or fibre is getting bent, says Parthasarathi: “The health and the integrity of the fibre plant, there are so many things that affect a transmission.”
Operators may have monitoring infrastructure in place but not necessarily the monitoring of the signal integrity or the physical infrastructure. “If you have an existing network, this is a very easy way to add a monitoring capability,” says Parthasarathi.
“As we can control all the parts – the optical channel monitoring and the OTDR – we can configure it [the platform] to meet the application,” adds Sara Gabba, manager, analysis, intelligence & strategic marcom at II-VI. “Coherent indeed provides a lot of information, but this kind of unit is also suitable for access network applications.”
The optical monitoring system features an optical switch so it can cycle and monitor up to 48 ports.
With operators adopting disaggregated designs, each element in the optical network is required to have more intelligence and more autonomy.
“If you can provide this kind of intelligent monitoring and provide information about a specific link, you create the possibility to be more flexible,” says Gabba.
Using the monitoring platform, intelligence can be more widely distributed in the optical network complementing systems operators may have already deployed, she adds.