Los Angeles, March 24 2015—At the annual OFC panel session for press and analysts, Facebook's network architect Yuval Bachar told the audience that prices for networking components such as pluggable optical modules cost too much. He needs the data rates that 100G provides and he wants optical links in Facebook's datacenters. He told these problems to representatives of a startup silicon-photonics company and an established maker of ICs.
"Our growth rate is enormous," said Bachar, "much larger than those of service providers and others with large datacenters. Our datacenters are growing at 2x to 3x every eight to ten months. We often skip a new technology and go to the next one. For example, 40G doesn't work for us anymore. We can scale our networks for about another year, but then we'll need 100G." Unfortunately, 100G is still relatively new and with it comes the high cost of optical pluggable modules.
As a result, Bachar is looking to silicon photonics. That, he said could get Facebook to move to 100 Gbps, 400 Gbps, and 1 Tbps data rates at the pace it needs, which is a speed upgrade every 12 to 18 months. He also wants to replace the existing multimode fiber infrastructure with less expensive single-mode duplex fiber. "Now, we have some six-to-eight vendors that can supply the [electrical/optical] conversion modules at a reasonable cost. They get us closer to what we want, which is $1 per 1 Gbps. Prices are now low enough for us to move to single-mode duplex fiber."
At an OFC 2015 panel session, Facebook's Yuval Bechar (second from left) told moderator Daryl Innis (left), Greg Fish (second from right) and Flavio Benetti (far right) that Facebook needs to increase data rates while lowering network costs.
"At the same time," he continued, "we want our suppliers to make money so they can continue to supply is with the components we need. We're looking to reduce costs by eliminating the middleman and buy directly from the manufacturers. There is a huge markup, making optical modules very expensive."
Panel moderator Daryl Innis noted that prices for lower-speeds [1 Gbps and 10 Gbps] optical modules have dropped dramatically and he's now seeing price reductions at higher speeds.
Greg Fish, CTO of silicon-photonics provider Aurrion responded by saying "Photonics needs to work more like electronics. We've designed a product that is more like an electronic product than a photonic product. We have a photonics design kit that lets us make circuits. We need to stop designing every new photonic device." Fish said that this concept could branch out beyond the datacenter to consumer devices. "Photonics needs to be built in fabs that have very high volume and low cost structures. It needs to get out of pluggable modules and get onto boards. Once that happens, we can scale it to meet Facebook's needs." He also noted that operators of datacenters that have multimode fiber hesitate to remove it because of the cost. Anyone installing new fiber is doing to use single-mode fiber because of the lower cost of optical modules. Single-mode optics must then scale to higher and higher data rates.
Innis then introduced Flavio Benetti, general manager of STMicroelectronics' Mixed Processes Division. "Flavio is a CMOS guy who is bringing optics into his facilities."
"We need to make silicon photonics as close the electronic technology as possible. Said Benetti "It needs to get out of the lab and into the fab. In a few months, we will be releasing a product for 100G that's based on silicon photonics. This is a first step."
"Can you support a 12-to-18 month cycle?" Innis asked Fish and Benetti. Benetti responded by saying "once the technology is online, we will be able to support such a cycle. Integrating silicon photonics into traditional CMOS fabs has been easier than we originally thought."
An audience member noted that some system manufacturers populate their boards with as many optical modules as needed for an order. Why would Facebook want to go purchase systems that integrate optical converters on the boards? Bachar responded that Facebook always buys line card that are fully populated with optical modules. "We can't afford the electrical-optical interface modules, not at $2000 each [for $100 Gbps]," which is why he'd like optics integrated into boards rather than buy modules. Pluggable modules won't, according to Bachar, be a viable solution because of cost, heat dissipation, and faceplate density. When a link fails, however, a technician and simply replace a failed module without having to replace an entire board. As a result, Facebook will continute trying to drive down the cost of pluggable optical modules.
—Martin Rowe, Senior Technical Editor