The present and future of optical interconnects. Source: Synopsys

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 Broadcom’s design for co-packaged optics. Source: Broadcom

Rethinking interconnects
Broadcom’s solution is to take eight 800 Gb transceivers and consolidate them into a single optical 6.4T optical engine (OE) and integrate them on a common substrate with the switch ASIC in order to provide all of the optical connectivity that’s needed for a system. For a 51.2T switch you would then need eight of these 6.4T optical engines.

Several start-ups are also tackling optical interconnect problems.

Celestial AI has an optical interconnect solution, as well, which the company claims is more thermally stable than the ring resonators currently used in transporting optical signals, and which should allow closer communication with ASICs. “We’re providing optical connectivity all the way to the point of compute,” explained Celestial AI CEO David Lazovsky. “A lot of the companies that are in the co-packaged optics space work on a wire-forwarding technology, meaning you send me a signal electronically and all I’m going to do is convert that to optics and drop it off in an electronic signal at the other end of the fiber. At Celestial AI, we are a full stack solution. We have a protocol adaptive layer to provide compatibility with our customers’ existing infrastructures.”

  Photonic fabric configurations. Source: Celestial AI

New ideas emerging
Along with the reliance on older protocols and the persistence of multi-mode fibers, the industry is moving forward.

In August, OIF announced the External Laser Small Form-Factor Pluggable (ELSFP) Implementation Agreement (IA), which defined a front-panel pluggable form factor tailored to co-packaged optical systems and other multiple laser external laser source applications.

According to the OIF, IA includes definitions for the placement of laser sources at the front panel, the coolest section of the system, enhancing system reliability and allowing for efficient “hot-swap” field replacement when necessary.

“These are used for the emerging high-density optics that are commonly found in applications such as artificial intelligence and machine learning,” said Calvin. “Basically, these are the emerging interconnects that are used inside hyperscale data centers that are moving the needle in this industry right now with extremely low-latency, high-speed, high-performance requirements.”

 https://semiengineering.com/ai-drives-need-for-optical-interconnects-in-data-centers/