With their high speed and low power requirements, optical interconnects will someday provide the ultimate form of communication between components on a silicon microprocessor chip. However, this will only happen when microphotonic components and networks can be fabricated using processes that meld well with those for microelectronics. Researchers at Cornell University (Ithaca, NY) have figured out a way to fabricate one vital photonic component, a silicon high-speed waveguide integrated electro-optic modulator (EOM), in a microphotonics-friendly manner. While previous devices were made on single-crystal silicon-on-insulator wafers (not a good platform for combined photonics and electronics), the new EOM is fabricated on a film of silicon that can be deposited atop the electronics layer.
In the prototype, a p+-n--n+ diode was embedded around a polysilicon ring resonator evanescently coupled into an adjacent waveguide, enabling subnanosecond optical modulation. Fabrication was using standard microelectronic processes. The polysilicon grain boundaries and defects decreased the carrier-combination lifetime and thus sped up the modulator when compared to a single-crystalline device. The researchers measured a 2.5 Gbit/s modulation speed and a 10 dB modulation depth, with an estimated 6 dB insertion loss, a power consumption of 2.4 mW, and an energy consumption of 950 fJ/bit. An improved version should reach a speed of tens of Gbit/s and an insertion loss near 0 dB. Contact Michal Lipson at email@example.com.