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Very interesting points. Thanks. Maybe in the future we will have high bandwidth chip to chip standards (like PCIe, and network chip to chip standards like XFI

Very interesting points. Thanks. Maybe in the future we will have high bandwidth chip to chip standards (like PCIe, and network chip to chip standards like XFI) with optical communication for better latency, especially in large switches with latency constraints.

ggrrhh_ta 5y ago
There are several misconceptions (as pointed by others) relating the trade-off of electrical vs optical for interconnects. Optical interconnect are promising, and in fact, at some point they will become almost unavoidable: bandwidth vs path length. If you want to dive into the fundamental reasons, the following paper might help: https://www.researchgate.net/publication/224504016_Miller_D_Device_requirements_for_optical_interconnects_to_silicon_chips_Proc_IEEE_97_1166-1185 https://www.researchgate.net/publication/224504016_Miller_D_...
- mleonhard 5y ago
  Thank you for sharing that article. Miller p.4, says: > Typical results have energies per bit of 2 – 30 pJ/bit in recent demonstrations. (1 pJ/bit is the same as 1 mW/(Gb/s); the latter is a more common way of stating the unit in the electrical interconnect literature, though the former relates more obviously to the physics of the interconnect devices.) The best current results for transceivers are ~ 2.8 – 6.5 pJ/bit for board or backplane interconnects [17], and ~ 2 pJ/bit [16] for moderate length chip-to-chip interconnects with a relatively ideal electrical channel. Miller p.12: > Hence, from the above discussion of systems energy targets, we have optical device energy targets of 10 – 20 fJ/bit for off-chip interconnects, and ~ 2 – 10 fJ/bit for on-chip interconnects. Kiani's on-chip laser begins operating at 16mW of power. If the laser is part of a chip running at 5GHz, switching the laser at the same clock yields 5Gbit/s. This is 3.2 mW/(Gb/s) = 3.2 pJ/bit. This is still 3 orders of magnitude more than the 10 fJ/bit target.

ggrrhh_ta 5y ago

There are several misconceptions (as pointed by others) relating the trade-off of electrical vs optical for interconnects. Optical interconnect are promising, and in fact, at some point they will become almost unavoidable: bandwidth vs path length. If you want to dive into the fundamental reasons, the following paper might help: https://www.researchgate.net/publication/224504016_Miller_D_Device_requirements_for_optical_interconnects_to_silicon_chips_Proc_IEEE_97_1166-1185 https://www.researchgate.net/publication/224504016_Miller_D_...

mleonhard 5y ago
Thank you for sharing that article. Miller p.4, says: > Typical results have energies per bit of 2 – 30 pJ/bit in recent demonstrations. (1 pJ/bit is the same as 1 mW/(Gb/s); the latter is a more common way of stating the unit in the electrical interconnect literature, though the former relates more obviously to the physics of the interconnect devices.) The best current results for transceivers are ~ 2.8 – 6.5 pJ/bit for board or backplane interconnects [17], and ~ 2 pJ/bit [16] for moderate length chip-to-chip interconnects with a relatively ideal electrical channel. Miller p.12: > Hence, from the above discussion of systems energy targets, we have optical device energy targets of 10 – 20 fJ/bit for off-chip interconnects, and ~ 2 – 10 fJ/bit for on-chip interconnects. Kiani's on-chip laser begins operating at 16mW of power. If the laser is part of a chip running at 5GHz, switching the laser at the same clock yields 5Gbit/s. This is 3.2 mW/(Gb/s) = 3.2 pJ/bit. This is still 3 orders of magnitude more than the 10 fJ/bit target.