Quantum-dot modulator drives power requirements even lower

Researchers at Stanford University (Stanford, CA) and the University of California–Santa Barbara (UCSB) have developed a proof-of-concept electro-optic modulator based on a single quantum dot that could operate at only 1 fJ/bit–two orders of magnitude lower than state-of-the-art 400 fJ/bit silicon microring modulators from Sun Microsystems (Santa Clara, CA) and colleagues.

Instead of modulating the transmission of light by controlling the resonance frequency of an entire resonator (free-carrier injection into a ring that is several tens of micrometers large–Sun's approach), the Stanford/UCSB team uses a lateral electric field to control (via the quantum-confined Stark effect) the resonance of a single nanometer-sized indium arsenide quantum dot coupled to a gallium arsenide photonic-crystal cavity. When resonant with the cavity, the quantum dot prohibits photons from passing through the cavity; when not resonant, it lets them pass through. An on/off switching ratio of 1.3:1 was achieved with a 10 V driving voltage at modulation speeds of 150 MHz. Switching ratios of 100:1, speeds up to 10 GHz, and optical power levels around 20 nW are theoretically possible by improving the quantum dot and cavity architecture. These devices could be made CMOS compatible using the emerging silicon/germanium platform. Contact Jelena Vuckovic at [email protected].