Start-up Ayar Labs, working with Intel, has interfaced its TeraPHY optical chiplet to the chip giant’s Stratix10 FPGA.
Hugo SalehIntel has teamed with several partners in addition to Ayar Labs for its FPGA-based silicon-in-package design, part of the US Defense Advanced Research Projects Agency’s (DARPA) project.
Ayar Labs used the Hot Chips conference, held in Palo Alto, California in August, to detail its first TeraPHY chiplet product and its interface to the high-end FPGA.
Origins
Ayar Labs was established to commercialise research that originated at MIT. The MIT team worked on integrating both photonics and electronics on a single die without changing the CMOS process.
The start-up has developed such building-block optical components in CMOS as a vertical coupler grating and a micro-ring resonator for modulation, while the electronic circuitry can be used to control and stabilise the ring resonator’s operation.
Ayar Labs has also developed an external laser source that provides an external light source that can power up to 256 optical channels, each operating at either 16, 25 or 32 gigabits-per-second (Gbps).
The company has two strategic investors: Intel Capital, the investment arm of Intel, and semiconductor firm GlobalFoundries.
The start-up received $24 million in funding late last year and has used the funding to open a second office in Santa Clara, California, and double its staff to about 40.
Markets
Ayar Labs has identified four markets for its silicon photonics technology.
The first is the military, aerospace and government market segment. Indeed, the Intel FPGA system-in-package is for a phased-array radar application.
Two further markets are high-performance computing and artificial intelligence, and telecommunications and the cloud.
Computer vision and advanced driver assisted systems is the fourth market segment. Here, the start-up's expertise in silicon photonics is not for optical I/O but a sensor for LIDAR, says Hugo Saleh, Ayar Labs’ vice president of marketing and business development.
Stratix 10 system-in-package
The Intel phased-array radar system-in-package is designed to takes in huge amounts of RF data that is down-converted and digitised using an RF chiplet. The data is then pre-processed on the FPGA and sent optically using Ayar Labs’ TeraPHY chiplets for further processing in the cloud.
Source: Ayar Labs, Intel
“To digitise all that information you need multiple TeraPHY chiplets per FPGA to pull the information back into the cloud,” says Saleh. A single phased-array radar can use as many as 50,000 FPGAs.
Such a radar design can be applied to civilian and to military applications where it can track 10,000s of objects.
Moreover, it is not just FPGAs that the TeraPHY chiplet can be interfaced to.
Large aerospace companies developing flight control systems also develop their own ASICs. “Almost every single aerospace company we have talked to as part of our collaboration with Intel has said they have custom ASICs,” says Saleh. “They want to know how they can procure, package and test the chiplets and bring them to market.”
It is one thing to integrate a chiplet but photonics is tricky
TeraPHY chiplet
Two Intel-developed technologies are used to interface the TeraPHY chiplet to the Stratix 10 FPGA.
The first is Intel’s Advanced Interface Bus (AIB), a parallel electrical interface technology. The second is the Embedded Multi-die Interconnect Bridge (EMIB) which supports the dense I/O needed to interface the main chip, in this case, the FPGA to a chiplet.
EMIB is a sliver of silicon designed to support I/O. The EMIBs are embedded in an organic substrate on which the dies sit; one is for each chiplet-FPGA interface. The EMIB supports various bump pitches to enable dense I/O connections.
Ayar Labs’ first TeraPHY product uses 24 AIB cells for its electrical interface. Each cell supports 20 channels, each operating at 2Gbps. The result is that each cell supports 40Gbps and the overall electrical bandwidth of the chiplet is 960 gigabits.
The TeraPHY’s optical interface uses 10 transmitter-receiver pairs, each pair supporting 8 optical channels that can operate at 16Gbps, 25Gbps or 32Gbps. The result is that the TeraPHY support a total optical bandwidth ranging from 1.28Tbps to 2.56Tbps.
The optical bandwidth is deliberately higher than the electrical bandwidth, says Saleh: “Just because you have ten [transmit/ receive] macros on the die doesn't mean you have to use all ten.”
Also, the chiplet supports a crossbar switch that allows one-to-many connections such that an electrical channel can be sent out on more than one optical interface and vice versa.
For the Intel FPGA system-in-package, two TeraPHY chiplets are used, each supporting 16Gbps channels such that the chiplet’s total optical I/O is up to 5.12 terabits.
Ramifications
Saleh stresses the achievement in integrating optics in-package: “It is one thing to integrate a chiplet but photonics is tricky.”
Ayar Labs flip-chips its silicon and etches on the backside. “Besides all the hard work that goes into figuring how to do that, and keeping it hermetically sealed, you still have to escape light,” he says. “Escaping light out of the package that is intended to be high volume requires significant engineering work.” This required working very closely with Intel’s packaging department.
Now the challenge is to take the demonstrator chip to volume manufacturing.
Saleh also points to a more fundamental change that will need to take place with the advent of chip designs using optical I/O.
Over many years compute power in the form of advanced microprocessors that incorporate ever more CPU cores has doubled every two years or so. In contrast, I/O has advanced at a much slower pace - 5 or 10 per cent annually.
This has resulted in application software for high-performance computing being written to take this BW-compute disparity into account, reducing the number of memory accesses and minimising I/O transactions.
“Software now has to be architected to take advantage of all this new performance and all this new bandwidth,” he says. “We are going to see tremendous gains in performance because of it.”
Ayar Labs says it is on schedule to deliver its first TeraPHY chiplet product in volume to lead customers by the second half of 2020.