ROY RUBENSTEIN SILICON PHOTONICS
INTEL first tomarket with integrated laser silicon photonics products
ROY RUBENSTEIN
Intel’s breakthrough 100G silicon photonics
modules are the first high-volume
application of a hybrid integration technique.
I ntel has unveiled its first silicon photonics 100-gigabit optical modules for the data centre. The modules mark the first high- volume application of a hybrid integration technique whereby III-V materials such as indium phosphide are bonded onto a silicon substrate before being processed. Known as heterogenous integration, the technique allows optical functions such as the laser to be manufactured and integrated on-chip. Intel’s 100-gigabit modules announcement follows the news that Juniper Networks has entered into an agreement to acquire U.S. silicon photonics start-up Aurrion for $165 million. Aurrion is another silicon photonics player developing heterogenous integrated products. HETEROGENOUS INTEGRATION John Bowers is a co-founder of Aurrion. He is also a professor in the Department of Electrical and Computer Engineering at the University of California, Santa Barbara, and has worked with Intel on heterogeneous integration. Bowers says that the attraction of the bonding technique is that it allows features to be integrated onto silicon that haven’t been widely integrated onto any other platform. These include not only lasers but other active devices such as modulators and photo-detectors, as well as passive functions such as isolators and circulators. Intel is using the technique to integrate the laser for its 100-gigabit transceiver designs. “Once we apply the light-emitting material down to the silicon base wafer, we define the laser in silicon,” says Alexis Bjorlin, vice president and general manager, Intel Connectivity Group. “There is no alignment needed; we align the laser with lithography.” 100-gigabit modules Intel is already shipping its 100-gigabit PSM4 module to customers. “First volume shipments are happening now,” says Bjorlin. One cloud service provider adopting Intel’s PSM4 is Microsoft. The chip company is also sampling a 100-gigabit CWDM4 module that also
meets the more demanding CLR4 Alliance’s optical specification. Used as a CLR4 module, no forward-error correction is needed, making it suited for low-latency applications such as high- performance computing. Intel is not the first vendor to offer PSM4 modules, nor is it the first to use silicon photonics for such modules. Luxtera and Lumentum are shipping silicon photonics PSM4 modules, while STMicroelectronics is supplying its PSM4 optical engine chip. “Other vendors have
Intel’s 100G silicon photonics modules.
been shipping PSM4 modules for years, including large quantities at 40 gigabit,” says Dale Murray, principal analyst at LightCounting Market Research. “Luxtera has the clear lead in silicon-photonic- based PSM4 modules but a number of others are shipping them based on conventional optics.” The PSM4 is implemented using four independent 25-gigabit channels sent over a single-mode ribbon fibre. Four fibres are used for transmit and four for receive. The PSM4 configuration can share a single laser across the four output fibres. MARKET DEMAND Bjorlin says the PSM4 and the CWDM4/ CLR4 will play a role in the data centre. There are applications where being able to break out 100-gigabit into 25-gigabit signals is useful while other data centre operators prefer a duplex design due to the efficiency of fibre use. “We are right at the cusp of the real 100-gigabit connectivity deployments,” she says. Meanwhile, Juniper’s acquisition of Aurrion is the latest in a series of systems vendors bringing silicon photonics in- house. Aurrion has made tunable lasers for telecom that cover both the C- and L-bands, as well as uncooled laser arrays for datacom applications. The start-up has also been developing high-speed
100-gigabit data centre transceivers. Juniper has yet to detail its plans for Aurrion. The systems vendor could choose to make its own optical transceivers but, more likely, it will use silicon photonics as part of its switch designs to tackle issues of data-centre scaling. This is an opportunity Intel is eyeing for its silicon photonics technology. Leading switch silicon supports 3.2 terabits of capacity and this will increase to 6.4 terabits by next year and 12.8 terabits using 4-level pulse-amplitude modulation (PAM-4) signalling by 2018. And in 2020, 25.6 terabit switch chips are expected. The current data centre demand for 100-gigabit is for modules that plug into the front panels of switches but the market is evolving to 400-gigabit on-board optics, says Bjorlin, to support the emerging higher-capacity switches. “When you get to 25.6 terabit switches, you start to have a real problem getting the electrical signals in and out of the switch chip,” says Bjorlin. This is where silicon photonics can play a role by co-packaging the optics alongside the switch silicon. “Ultimately that co-packaging is inevitable,” she says. Professor Bowers offers a broader perspective: “Where Intel and Aurrion are going is getting to the point where photonics will be ubiquitous, high-yielding and cheap.”
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| ISSUE 7 | Q3 2016
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