Sub-diffraction Focusing with Propagating Waves

Alex Wong

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

Abstract:

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.

 

Biography:

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.