In what could prove to be of major importance to the future of motherboard and component data transfer rates, the Photonics Technology Lab at Intel has announced a silicon laser modulator that can encode data at 40Gb/sec.

According to Dr. Ansheng Liu, Principal Engineer with the Intel Corporate Technology Group and a former NASA Ames Research Center engineer, "the photonic integrated circuit (PIC) could provide a cost-effective solution for optical communication and future optical interconnects in computing industry." PICs on silicon platforms in particular have been the focus of much attention and excitement within the research community because of the low cost coupled to the potential for high volume manufacturing. "Competition in this arena is intense as many players in both academia and industry have been aggressively pursuing research into completely integrated CMOS photonics" adds Liu.

A key component of any silicon PIC is a high-speed silicon optical modulator, required in order to encode the data on the optical beam. The reason why the Intel breakthrough is just that can be clarified if you take a look at the state of play with current silcion optical modulators. Not only are they expensive to produce courtesy of the materials used, such things as lithium niobate and III-V compound semiconductors do not come cheap apparently, but they are also just as fast.

Unfortunately, it has been impossible to squeeze anything approaching this turn of speed out of silicon until now. Crystalline silicon just does not have the linear electro-optic ability to modulate light and so the search has been on for a way to ramp up the transfer rate using the less effective free-carrier plasma dispersion effect instead. Liu and his team have finally managed to match the 40Gb/sec mark by combining the free-carrier manipulation effect with a unique traveling wave drive system.

If you want to get really technical, here is what Liu says about it: "the Intel modulator is based on a Mach-Zehnder interferometer with a reverse-biased pn junction in each of the arms. When a reverse voltage is applied to the junction, free carriers – electrons and holes resulting from the n- and p-dopants – are pulled out of the junction, changing its refractive index via the free-carrier effect. The intensity of the light transmitted through the Mach-Zehnder interferometer is modulated by modulating the phase difference between the interferometer’s two arms. This modulation can be very fast, because free carriers can be swept out of the junction with a time of approximately 7 ps. The modulator speed is thus limited by the parasitic effects such as RC time constant limit. To minimize the RC constant limitation, Intel researchers adopted a traveling-wave drive scheme allowing electrical and optical signal co-propagation along the waveguide. The traveling-wave electrode which is based on a coplanar waveguide was designed to match the velocity for both optical and electrical signals, while keeping the RF attenuation small."

There, I am sure you feel much more informed now.

Seriously though, the important thing is that the device could, and should, eventually find its way into the computers of the future, integrating multiple devices on one chip that is capable of moving terabits of aggregate data every second.