Optical active cable exploits CMOS photonics

28 Aug 2007

A new 40 Gbit/s cable is paving the way for CMOS photonics to be used in consumer products.

40G connector

Luxtera is claiming that its new optical active cable is the first product to exploit CMOS photonics for an industrial application. CMOS photonics allows photons and electrons to be processed on a common wafer.

"We implement both traditional transceiver electronics, such as amplifiers and serializers, alongside optical waveguides and modulators on the same CMOS die," Marek Tlalka of Luxtera explained to optics.org. "This drives down both the cost and the power consumption of the transceivers."

Optical active cables are complete cable assemblies which convert electrical signals to optical signals and vice versa inside the connectors at each end. "The advantage is that they can connect to the same receptacles as copper cable, but provide users with longer reach and lower error rates," said Tlalka. "They also eliminate environmental concerns, as the optical interface is closed to the user."

The new cable is claimed to have a reach of 300 meters, and achieves its 40 Gbit/s bandwidth by having four singlemode fibers of 10 Gbit/s each. Four 10G transmitters and four 10G receivers are located on the chip.

"We can split light from a single laser, or we can put two lasers on a single die driving more than four lanes each," said Tlalka. "So adding more transmitters or receivers is just a silicon size exercise. We envision a 100G transceiver, 10x10G, using this technology in the next few years."

40G cable

The laser source is the only element that cannot be implemented in CMOS because CMOS lacks sufficient light-generating properties, so Luxtera attaches an off-the-shelf 1550 nm DFB laser to the surface of the die. "Our laser is always on, and we modulate the light inside the waveguides on the chip," Tlalka pointed out. "This means we can take one laser and split the light four ways, powering four independent transmitters and sharing the cost of a single laser across them."

The cable will be available in production quantities in 2008, and other applications are under development. "Because of the dramatic cost reductions associated with CMOS photonics technologies, we plan to introduce optics to consumer applications and bring a product to that market next year."