Nanoscale Photodetector and Optical Modulator for Future Optical Interconnect Systems

As the demand for cheaper and faster computing continues to increase, the semiconductor industry has relied on transistor scaling to meet this demand. With transistor size approaching the atomic limit, there needs to be a fundamental change from the traditional improvement methods employed in the past. Improvement of data transfer between the microprocessor and other peripheral units could provide an immediate boost to computing speed. The bus lines connecting the CPU to other components are made up of metal interconnects. The speed of metal interconnects are highly limited due to parasitic effects. Switching to optical interconnects will eliminate most of the parasitic effects experienced with metal interconnects and will provide an immediate improvement in computing speed.

To implement an optical interconnect system, nanoscale photodetectors and modulators will be required. We have demonstrated a single 20nm diameter germanium nanowire photodetector, with current gain of more than 103 and responsivity of 25A/W, operating at 1.55um wavelength. The device photocurrent is highly scalable based on the number of active nanowires connected in a parallel formation. We have also demonstrated a multilevel modulating device based on the integration of two memristors on a photonic crystal waveguide. Our device enabled the modulation of an optical channel by multiple electrical signals with distinct optical output for every combination of the modulating input signals. The demonstrated device operates at the telecommunication wavelength of 1.55um.

Integration of nanowire photodetector and nanoscale modulator as a single device will potentially enable high-speed and high-density optical interconnect link between the microprocessor and other peripheral units.