OFC in San Diego-A review
A lot of phonons bounced off the walls at OFC discussions on how to continue reducing the power consumption of optics: from long haul coherent systems to interconnects in AI Clusters.
Several equipment manufacturers announced their achievements over the last two weeks. Cisco (Acacia) was the first to reach 1.2T/wavelength performance in a product, announcing CIM8 modules more than a year ago, and the company disclosed first shipments of CIM8 in January 2023. Fujitsu, Infinera and Nokia introduced their 1.2T/wavelength solutions, while Ciena announced its 1.6T/wavelength technology in February 2023, as summarized in the table below.
Coherent Terabit Announcements and Product Status
|DSP technology||5 nm CMOS||5 nm CMOS||3 nm CMOS||5 nm CMOS||5 nm CMOS|
|Modulator technology||Silicon Photonics||Silicon Photonics||InP and/or
|Availability||Early 2023||Q4 2023||H1 2024||H1 2024||H1 2023|
Ciena chose to skip 5nm CMOS so their WaveLogic6 DSP will be based on 3nm technology, which is just becoming available. The company is developing 200Gbaud optical chips using InP and TFLN material in parallel. One solution may be a better option for the pluggables and another for board-mounted modules. We will have to wait and see.
Fujitsu, Infinera and Nokia selected 5nm CMOS for their new DSP and 140Gbaud for their optical chips, following Cisco’s strategy. Just like Cisco, Nokia is using silicon photonics technology, but Infinera continues to explore the limits of InP. LightCounting did not yet have a chance to interview Fujitsu on their design of their optics.
Reducing power consumption is the main benefit of these new coherent solutions, as illustrated in the figure below. If this chart attracts the attention of “green extremists”, 100G/wavelength technology may be outlawed. The contribution of DWDM optics to climate change is debatable, but the power savings enabled by the latest solutions are impressive.
Improvements in spectral efficiency are a lot more modest. Three of 1.6T/wavelength channels with 200Gbaud optics are probably just as wide in spectrum as four of 1.2T/wavelength channels with 140Gbaud optics, delivering 4.8T in total bandwidth. There must be some separation between each of the channels and the math is a bit more complicated than it looks. Careful measurements of spectral efficiency are a lot more complicated, offering the vendors many options to argue with in favor of their solutions. All the solutions must be around 8bit/Hz by now – very close to the Shannon limit.
Coherent will have a live demo of 100G coherent ZR modules with power consumption below 5W, designed with the QSFP28 form factor in mind. We will see if this really works. If it does, coherent technology may be an option for intra-datacenter connections at some point.
Lucidean – a new start-up will be discussing their plans for commercializing DSP-free coherent technology at OFC this year. If this approach is successful, we may not need 3nm CMOS.
There will be several other start-up companies making their debut at OFC 2023: Alfalume, Casela Technologies, Nubis Communications and Xscape Photonics are just some of them which have been spotted by LightCounting so far. There will be more for all of us to discover at OFC.
The start-up companies mentioned above are developing components and modules for co-packaged optics (CPO) – the hottest topic in the industry now. Success of CPO is not guaranteed, but even just the idea of CPO has re-energized the industry and especially the enthusiasts of pluggable optical transceivers, led by Andy Bechtolsheim.
Two months after Broadcom announced plans for 3.2T CPO engines in January 2021, Andy surprised all of us at OFC 2021 by introducing the OSFP-XD form factor designed with 3.2T pluggable transceivers in mind. Andy may have more surprises for us this year, He will be giving numerous presentation at OFC, including one in a panel moderated by LightCounting: Optics in Future AI Systems (Tuesday, March 7th, 10:45-11:45 at Theater II on the show floor).
Direct drive CPO, demonstrated by Broadcom at OFC 2022, offers significant reductions in power consumption, as illustrated in the figure below.
Most of the reduction in energy per bit demonstrated by Broadcom comes from DSP-free (direct drive) optical engines. There are rumors that DSP- free (linear drive) pluggable transceivers can match CPO performance. It sounds too good to be true, but we expect to see its first test results next week. Linear drive technology will certainly be a new hot topic at OFC 2023.
LightCounting is organizing a 2-hour webinar on Linear Drive technology on March 21st at 5pm PST. We will have an excellent line up of speakers on hand to sort out all the OFC announcements on this topic. Please register here if you are interested in joining us.
AI Clusters are starved for connectivity bandwidth. If the optics have a play, it has to consider non-standard approaches, along the lines of the CPOs, developed by Ayar Labs and IBM, also included in the figure above.
Removing the DSP is a step in the right direction, but innovation will not stop there. Technology development is not a sprint, it is a marathon. An iron man marathon for some, half marathon for others, but a marathon nevertheless.
Based on a blog by Dr. Vladimir Kozlov, founder and CEO, LightCounting
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