Light control in semiconductor could lead to optical transistor

Montreal, QC, Canada--At McGill University, Ph.D. candidate Jonathan Saari, professor Patanjali Kambhampati, and colleagues have shown that all-optical modulation and basic Boolean logic functionality (key steps in the processing and generation of signals) can be achieved by using input laser pulses to manipulate the quantum-mechanical state of a semiconductor quantum dot (QD).¹ Modulation rates near 1 THz were achieved.

In the experiment, femtosecond pulse sequences were used to control multiexciton populations, which modulated the resulting stimulated light emission at high speed. This is the optical analog of an electronic transistor, in which a small amount of input current influences a larger amount of current to turn on and off at high speeds (although normally in the gigahertz range--far from the terahertz range possible with optical transistors).

The researchers created two optically driven devices: and AND gate and an inverter.

"Our findings show that these nanocrystals can form a completely new platform for optical logic," says Saari. "We're still at the nascent stages, but this could mark a significant step toward optical transistors."

"These results demonstrate the proof of the concept," Kambhampati says. "Now we are working to extend these results to integrated devices, and to generate more complex gates in hopes of making a true optical transistor."

The findings build on a 2009 paper by Kambhampati's research group in Physical Review Letters. That work revealed previously unobserved light-amplification properties unique to QDs.

REFERENCE:

1. Jonathan I. Saari et al., Nano Letters, 13(2), p.722 (2013).