Luxtera Inc. is ready to demo a 100Gbit/s silicon photonics chip that could be used in transceiver modules, although the company is also eyeing the optical backplane market.

Silicon photonics is a slight misnomer, since some elements aren't silicon -- the germanium photodetectors, for instance. More properly, the chip is made of complementary metal-oxide semiconductor (CMOS) photonics, meaning it's built from the same manufacturing processes as ordinary electronics chips.

The chip, measuring 5mm by 6mm, produces four lanes each carrying 28 Gbit/s of traffic. A separate laser has to be attached to the die, but this can be an inexpensive, continuous-wavelength laser. Luxtera has been using one designed for 2.5Gbit/s fiber-to-the-home networks. The laser shines downward into waveguides that send it through Mach-Zender Modulators.

For the receiving side, the chip uses the same embedded photodetectors that Luxtera has been using at 10 Gbit/s and 14 Gbit/s.

To be used on a backplane, the chip would be placed inside a package that would be wire-bonded to the printed circuit board, next to the switching electronics. Pigtail optical fibers sticking out of the package would connect to the optical backplane itself, which consists of fibers embedded in a mylar-like material.



Why this matters
Optical backplanes are an intriguing idea that hasn't taken off beyond esoteric core-router types of markets. But vendors are starting to design optical backplanes into more systems, says Marek Tlalka, Luxtera's vice president of marketing. It's possible that silicon photonics could accelerate those efforts.

The more interesting step would be for the photonics to get integrated into the switch chip. After all, that's the promise of CMOS photonics -- the ability to merge photonics chips with electronics, all in the same manufacturing process, to take advantage of Moore's Law.

To do that, someone like Broadcom Corp. (Nasdaq: BRCM), the leader in switch chips, could license the CMOS-photonics manufacturing process from Luxtera, Tlalek says. But one can't help wondering if Broadcom might also consider doing this technology on its own or eventually acquiring it from someone like Luxtera.

Aside from all the backplane stuff, the 100Gbit/s CMOS transceiver would obviously be a candidate to go into 100Gbit/s optical modules or active optical cables. In the latter case, Luxtera would sell transceiver chips to someone like Molex Inc. (Nasdaq: MOLX), which has taken over Luxtera's active optical cables business.

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— Craig Matsumoto, West Coast Editor, Light Reading