Davis receives NSF grant for nanofabricated, all-optical devices

ISR-affiliated Professor Christopher Davis (ECE) is the principal investigator for a new National Science Foundation award, "NIRT: Nanofabricated All-Optical Computing, Switching, and Signal Processing Devices Based on Single Photon Tunneling." This is a four-year, $1.2 million award. Co-PIs are ECE Professor John Melngailis; ECE Assistant Research Scientist Igor Smolyaninov; Alexei A. Maradudin from the University of California, Irvine; and Andrei V. Stanishevsky from the University of Alabama at Birmingham.

A new and important phenomenon involving single photon tunneling has been discovered recently by a multidisciplinary team of researchers at the University of Maryland. Transmission of light through nanometer-scale pinholes in a gold film covered by a nonlinear dielectric saturates at a few thousand photons per second. The transmittance of such a nanometer-scale hole is nonlinear with light intensity, and at the single photon level corresponds to each photon in the process of being transmitted through the hole controlling the transmittance of successive photons. This result is analogous to the Coulomb blockade observed in single electron tunneling experiments. The phenomenon was initially observed only for random nanoscale pinholes that occur naturally in thin evaporated gold films.

Further work has shown that the transmittance of both individual nanofabricated holes (nanopores), and arrays of nanopores, both made by focused ion-beam nanaofabrication techniques, has shown not only the simple iiphoton-blockadel effects, but also controlled photon transmission. For example, the transmittance of a nanopore or nanopore array at one wavelength can be controlled by illumination with a second, different, wavelength. In this project a multidisciplinary team of optical scientists, theorists and nanofabricators will study of this new phenomenon and explore potential applications based on fabricated nanopores or arrays of nanopores in metal films. They expect that a detailed study of optical properties of such well-controlled nanopore and other nanostructures will reveal novel quantum phenomena in nonlinear optical transmission. For example, electrons in a Coulomb blockade tunnel one at a time, at more or less fixed time intervals. If photons tunneling through nonlinear optical nanopores show similar behavior (as an initial experiments suggest), the fabricated nanopores will become very unusual and useful light sources emitting individual photon periodically, one at a time.

Such controlled light sources are being actively pursued by researchers in the areas of quantum communication and quantum cryptography. In addition, novel and potentially important applications of nonlinear nanopore materials may also be expected in the areas of optical communications and all-optical signal processing. Optical signal processing relies on nonlinear interactions of light, which usually happen at very high optical intensities. Preliminary results indicate that the local optical field in a nanopore is enhanced by at least six or eight orders of magnitude, enabling nonlinear optical interactions to occur at much lower illuminating light intensities. This opens the door to devices where light is used to gate light, which they have already demonstrated at a fundamental level. Thus, a great number of optical communication and optical signal processing devices, such as all-optical switches, and signal and image processing devices, may be realized on a microscopic scale, and at much smaller operating optical powers than macro-devices.

Published August 1, 2003