Data and Time May 10 , 2011, 3:00-4:15 PM
Location Sanford Flemming Building, Room B560
Host Leon Yuan

Sub-diffraction Focusing with Propagating Waves

Alex Wong

The Edward S. Rogers Sr. Department of Electrical and Computer Engineering (Electromagnetics)


Both Heisenberg uncertainty and the electromagnetic diffraction limit are consequences of an underlying mathematical uncertainty principle, which states that a function cannot be simultaneously localized in a real space and its reciprocal space. For example, a waveform tightly localized in x-space cannot also be tightly localized in its spatial spectrum - the kx-space (kx = 2*pi/x). As a result, propagating waves, which are band-limited in k-space, are traditionally conceived as incapable of forming sharp focuses and high-resolution images. Hence most recent works on sub-diffraction focusing make use of evanescent waves, which unfortunately restricts their working distances to a fraction of the illumination wavelength.

In this talk I'll present my work towards focusing light beyond the diffraction limit with propagating waves - which will bring high-resolution imaging and lithographic capabilities to much larger working distances. I will argue that the key to such achievement lies in reconsidering this: what is the "localization", or "width", of a waveform, when it comes to applying the uncertainty principle? From this consideration, and drawing inspiration from the field of superdirective antennas, I'll show it's possible to focus light to a smaller spot than allowed by the diffraction limit. I'll present experimental focusing results in the microwave regime, and describe current effort towards an optical focusing experiment.



Alex Wong received a B.A.Sc. degree with honours from University of Toronto in Engineering Science (electrical option). During his undergraduate thesis research he worked under Prof. Li Qian on optical fiber-based pulse shaping algorithms. Following this he has earned his M.A.Sc. degree, and is currently in the PhD program in Electrical Engineering as a member of the Electromagnetics Group. His graduate research, supervised by Prof. George Eleftheriades, involves focusing electromagnetic waves beyond the diffraction limit for applications in imaging, sensing and lithography.