Intel's 50Gbps Silicon Photonics Link: The Future of Interfaces
by Brian Klug on July 30, 2010 6:49 AM EST- Posted in
- Trade Shows
- Intel
- Photonics
- Laser
Why use light instead of copper?
High speed PCB design is already a science in and of itself. Timing requirements dictate equal path lengths for a growing number traces between components, resulting in the ever familiar squiggly designs on desktop motherboards. Higher frequencies of course also require considerations about wave propagation through the medium - just like a transmission line. At 1 GHz, for example, one wavelength is about 0.14 meters for copper traces on FR-4, one of the most common PCB materials.
There’s also propagation delay - for wires, commonly given as 1 ns for every 6 inches of length, though different media have different wave propagation speeds due to the dielectric of the medium. I could go on about the challenges of very high frequency circuit design - which I’m not an expert in by any stretch of the mind.
The end takeaway is that traditional microelectronic designs are becoming physically constrained in size with higher and higher frequencies. You physically need to have the CPU close to the memory controller, northbridge, and other components for it to work at frequencies people expect. Move it relatively far (one wavelength) away, and the design challenges start to stretch microelectronics to its limit. Ultimately, designs sacrifice speed for distance, or vice versa.
The advantages of using optical interconnects instead of traditional copper traces are numerous. Using light instead of copper promises vastly higher bandwidth, reduced latency, resistance to electromagnetic interference, and potentially even power savings.
All of these reasons make using optical, silicon waveguides instead of copper traces an obvious choice. Instead of using numerous copper traces to connect the CPU to the northbridge, for example, one could envision using a single optical fiber. Or having many CPUs on one massive board connect to a chipset located even meters of path distance away. Or even have one room full of just CPUs and another room full of memory.
What Intel demonstrated on Tuesday is a working example of just that - an optical interconnect fabricated using the current traditional CMOS process, for connecting conventional electronics. Effectively an optical bus on silicon.
What’s different about Intel’s demonstration is that the lasers themselves are hybrid silicon.
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DanNeely - Friday, July 30, 2010 - link
I guess, it'd be nice to have this comment maybe include a citation to what other companies are already doing or planning on doing.Huron80 - Friday, July 30, 2010 - link
Look at Infinera, aren't they a networking provider?As stated in the article, Intel is taking what is being done effectively in Fiber Optic network transmissions - the same ones that help connect the internet - and are making a miniature version that will work inside your computer - the connections on the motherboard to components.
has407 - Friday, July 30, 2010 - link
Infinera's achievements are nothing to sneeze at, but they're quite different. AFAIK Infinera still uses a separate process for the optical components (the PIC, or "photonics IC"); they don't put everything on a single die. That's fine for certain markets, and they seem to have done well with Telecoms. However, for large scale low cost production; you're very unlikely to see it replace inter-chip or intra-chip interconnects in volume markets.Luxera is probably closer to what Intel is showing. They partnered with Freescale to integrate the photonics and electronics fab in CMOS last year to allow "low cost high volume" production"; exactly what may come from that is TBD. While we haven't seen much, Luxera's Blazar "Optical Active Cable" is a clue. But again, that's targeted at external inter-system connections; hard to tell if that's due to technology imitations or if Luxera is simply trying to generate revenue and build a market based on the technology is unclear.
In short, it's all about being able to produce everything--optical and electronic components--using a common and low cost fab. In that, Luxera/Freescale and Intel seem to be in the lead, and I'd wager Intel is most likely to bring it mainstream sooner rather than later.
This has the potential to significantly reduce the "interconnect tax" imposed by copper, which increases as speeds increase, and will soon be untenable. Intel said 20GHz was the ceiling for serial interconnects some years ago. (Teething problems related to power consumption with 10Gbe copper provide clues.) Even Inte's prediction is off by a factor of two, the end of that road is in sight.
At a guess, we'll see photonics integration in high-margin parts with the first replacing QPI as the backbone interconnect in high-end systems. Or maybe blade systems with optical backplanes. Or...
Jaybus - Friday, July 30, 2010 - link
Another thing to consider is that one reason for motherboards being as large as they are is that there must be hundreds of traces interconnecting components. Components have to be spread out to leave room for the traces. This technology will allow for one optical link to replace all of the myriad traces connecting the CPU to the northbridge, for example. Components can be closer together.Another factor is bus cards. Cards can be placed anywhere and connected by a single small fiber optic cable. Disk drives, etc. can be connected optically. This will substantially reduce the size of a full featured motherboard.
arnavvdesai - Friday, July 30, 2010 - link
While I agree components can be closer. We also have to think about the issue of heat dissipation. If we start moving items closer then we might have to deal with other issues.Jaybus - Monday, August 2, 2010 - link
Certainly, cooling will force a minimum size, but there is no reason an ATX board could not be shrunk to ITX size, at least, yet have even more i/o capability than a current ATX board. The board components could be placed as closely as is feasible, given the heat dissipation required.clarkn0va - Tuesday, August 3, 2010 - link
Doesn't replacing electrons with photons reduce the amount of heat produced?GullLars - Wednesday, August 4, 2010 - link
Not necessarily, you still need energy converting the digital electronic signal to optical and back, it's just the transport that saves energy, and only as much as the resistance in the copper wire. For high frequency or long distance information transport, it can be noticeable power savings.Regarding cooling, one quick solution is to switch the default from air cooling to liquid cooling in higher power systems. By placing the radiator, pump, and reservoir outside the system, and exploiting the new available dimension inside the case, you can make much smaller (and quieter while better cooled) systems.
Ninhalem - Friday, July 30, 2010 - link
The problem with a shrinking motherboard is that would leave too little room to put in cooling for the CPU and the memory. We're still a ways away from having CPUs running on light like the article said. I'm interested in not only shrinking the board a bit but having a different shape and orientation for the memory, video, audio card, and any other component you have in the case.Maybe have an upside down L shaped board where you can place the SATA II ports close to the hard drives and the optical drive. Maybe a start shaped board. Now that distance doesn't matter, the possibilities are endless. Very fascinating and exciting stuff.
darckhart - Friday, July 30, 2010 - link
sure, but they haven't talked about heat constraints yet.