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Dear 802.3df TF Participants,
The July Plenary meeting had detailed presentations on 800G 10km PMD approaches, enabling further discussion of Cost and Power.
Cost
The key PMD cost driver is the ASIC. A ZR Coherent ASIC is significantly higher cost and power than the same rate IMDD PHY ASIC (see email below). During the meeting, it was shown how to reduce ZR complexity by restricting reach to 10km, which requires a new ASIC. Unfortunately the resulting PHY volume is now three orders of magnitude lower than IMDD’s, instead of ZR’s two orders of magnitude lower, negating any comparative per die cost savings. Even more unfortunately, CMOS development cost, including masks, given projected PMD lifetime volumes raises serious questions about Economic Feasibility of a dedicated 10km ASIC.
Power
Eric’s presentation includes TX Loss, which enables comparison of Coherent and IMDD laser DC power.
TX Technology
TX Loss
Link Loss
TX + Link Loss
Effective Loss
after RX LOUnit
SiPh MZM Coherent
23
6.3
29.3
14.6
dB
InP EML IMDD
5
6.3
11.3
11.3
dB
Loss Difference
3.3
dB
A 40% efficiency of the TEC stabilizing the Coherent laser, results in the Coherent source requiring 5 times more DC power than the IMDD lasers.
Similar cost and power insights are likely behind the proposal from Chris Doerr, who understands Coherent as well as anyone, or better. For his PHY and TX, he proposes standard IMDD ASIC and EMLs, respectively.
Thank you
Chris
From: Chris Cole
Sent: Tuesday, April 05, 2022 5:18 PM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx
Cc: jdambrosia@xxxxxxxxx
Subject: RE: [802.3_B400G] Meeting Material Posted
Dear Task Force Participants,
During the 3/29/22 meeting, we started debating IMDD and Coherent alternatives for campus reach PMD.
In Transport, the debate was settled long ago as soon as the feasibility of Coherent was established. It’s obvious that eliminating DCFs and reducing the number of EDFAs is a good idea.
In Datacom, the CD, PMD and Sensitivity advantages of Coherent are not clear benefits, and Coherent is not an automatic choice. We have to do the hard work of analyzing technical and market trade-offs. Unfortunately, the 3/29/22 discussion was not a good start, so a reset is in order.
We know that when there is an FR interface, LR is not going to ship in the millions; it will ship in the tens of thousands. Similarly, we know that ZR interfaces don’t ship in the millions. Using LightCounting Vendor Survey Results through Q4 2021, 100G/200G Coherent volume was ~1⁄2 million over the last five years, which is less than 2% of the 100G IMDD Datacenter volume over the same time period.
This means neither an IMDD nor Coherent LR solution will have a dedicated DSP ASIC. IMDD 800G LR4 will use the same DSP ASIC as FR4 and DR4, because these will ship in the many millions. Coherent 800G LR1 will use the same DSP ASIC as ZR or ZR+ because those will ship in the tens and possibly hundreds of thousands. The IMDD DSP ASIC will be much lower cost than the ZR DSP ASIC because its volume will approach two orders of magnitude higher, like at 100G. We don’t have to speculate about the cost ratio of DSP ASICs at 800G; we have the answer at lower rates.
The specs on IMDD LR4 optics are more stringent than FR4, which raises cost. The Coherent LR TX source doesn’t have to be tunable, which lowers cost. However this fixed laser is nothing like an IMDD source, it has to be cooled and held to a precise wavelength otherwise it won’t match the RX LO.
The most interesting argument in favor of Coherent is that if nothing is done, the standard ZR solution works for LR, without the need for another code. This has both R&D and OpEx advantages.
Since the debate between IMDD and Coherent is likely to be replayed many times, let’s set a good example for the future by how we conduct it in .3df.
Thank you
Chris
From: John D'Ambrosia <jdambrosia@xxxxxxxxx>
Sent: Sunday, March 27, 2022 4:48 PM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx
Subject: [802.3_B400G] Meeting Material Posted
All,
Presentation material for our Task Force meeting on 29 March has been posted - https://www.ieee802.org/3/df/public/22_03/index.html [ieee802.org].
Please note that Mr. Williams presentation has undergone legal review by IEEE legal. Mr. Law and I will provide guidance regarding this presentation prior to Tom presenting, and ask that all comments are held to that time.
As a reminder, All interim teleconference meeting participants should review the following documents prior to participation in an interim meeting teleconference:
· IEEE SA patent policy
· IEEE SA Copyright Policy
· IEEE SA Participation Policy
All of these policies may be found at http://ieee802.org/3/policies.html [ieee802.org].
Regards,
John D’Ambrosia
Chair, IEEE P802.3df Task Force
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