Comment by cycomanic
7 months ago
It's important to note that wavelength channels are not coupled, so modems with different wavelengths don't need to be terribly close together (in fact one could theoretically do wavelength switching so they could be 100s of km apart). So the scaling we need to consider is the scaling of the MIMO which in current modems is 2x2. The difficulty is not necessarily just power consumption (also the power envelope of long haul modems is higher than the DCI modem you link, up to 70W IIRC), but also resourcing on the ASIC, your MIMO part (which needs to be highly parallel) will take up significant floorspace and you need to balance the delays.
The 38kW is not a very high number btw, the switches at the end points of submarine links are quite a bit more power hungry already.
Depending on phase matching criteria of lambda's on a given core, I would mostly agree that various wavelengths are not significantly coupled. I also agree there are a different power budget for LH modems vs. DCI, but power on LH modems is not something that often gets publicly disclosed. I am not too concerned with the overall power, more the power density (and component density) that 19 channel MIMO would require.
The main point I was trying to make is the impracticality of MIMO SDM. The topic has been discussed to death (see the endless papers from Nokia) and has yet to be deployed because the spatial gain is never worth the real world implementation issues.
Man, when switches are using tens of kilowatts, must be nice to have cheap water cooling all around!