As data transfer rates supported by the PCIe protocol are increasing, it is getting exceedingly hard to enable them over copper wires over longer distances. On Wednesday PCI-SIG announced formation of the PCI-SIG Optical Workgroup, which will prep PCIe for using optical interconnects. Over time PCIe optical interconnects will be particularly beneficial for artificial intelligence, datacenter, and high-performance computing applications.
Implementation of extended PCIe 5.0 (32 GT/s) connections in servers requires usage of PCIe 5.0 retimers due to signal degradation over increased distances, which generally reduces trace lengths of PCIe 5.0 interconnects when compared to older specifications. This distance can fluctuate based on the selection of materials and environmental conditions, but, in general, PCIe 5.0 retimers are common in modern AI and HPC machines. The challenge of signal integrity over copper interconnections becomes even more pronounced with the future introduction of PCIe 6.0 at 64 GT/s and PCIe 7.0 at 128 GT/s, which is why PCI-SIG is exploring alternatives in the form of optical interconnects.
The workgroup aims to remain optical technology-agnostic, accommodating various optical technologies and potentially creating technology-specific form-factors. Optical interconnects can potentially bring numerous benefits to PCIe and CXL connections, including improved performance, lower power consumption (PCIe 5.0 retimers consume well over 10W), extended reach, and reduced latency.
"Optical connections will be an important advancement for PCIe architecture as they will allow for higher performance, lower power consumption, extended reach and reduced latency," said Nathan Brookwood, a Research Fellow at Insight 64. "Many data-demanding markets and applications such as Cloud and Quantum Computing, Hyperscale Data Centers and High-Performance Computing will benefit from PCIe architecture leveraging optical connections."
While existing PCI-SIG workgroups continue their progression towards achieving a 128GT/s data rate in the PCIe 7.0 specification, the newly formed Optical Workgroup will focus on making PCIe architecture more compatible with optical technologies. At this point PCI SIG has not disclosed which version of PCIe will take advantage of optical interconnects.
"We have seen strong interest from the industry to broaden the reach of the established, multi-generational and power-efficient PCIe technology standard by enabling optical connections between applications," said PCI-SIG President and Chairperson Al Yanes. "PCI-SIG welcomes input from the industry and invites all PCI-SIG members to join the Optical Workgroup, share their expertise and help set specific workgroup goals and requirements."
