Kenneth Allen Defends his Dissertation

Kenneth Allen Defends his Dissertation

CfM researcher and UNCC Dr. Kenneth Allen successfully defended his Dissertation "Waveguide, Photodetector, and Imaging Applications of Microshperical Photonics"(October 29, 2014). Under the direction of his advisor Dr. Vasily Astratov, Professor, Department of Physics & Optical ScienceDr. Allen graduated December 2014 with his PhD in Optical Science & Engineering. 






Dielectric microspheres with diameters (D) on the order of several wavelengths of light (l) have attracted increasing attention from the photonics community due to their ability to produce extraordinarily tightly focused beams termed “photonic nanojets,” to be used as microlenses for achieving optical super-resolution or to develop sensors based on whispering gallery mode resonances. In this dissertation, we study the optical properties of more complicated structures formed by multiple spheres which can be assembled as linear chains, clusters or arrays, integrated with waveguides or embedded inside other materials to achieve new optical properties or device functionalities.

For linear chains of polystyrene microspheres (n=1.59), we observed a transition from the regime of geometrical optics (at D>20l) to the regime of wave optics (at D<20l). We showed that this transition is accompanied by a dramatic change of focusing and optical transport properties of microsphere-chain waveguides. The results are found to be in a qualitative agreement with numerical modeling.

We developed, designed, and tested a single-mode microprobe device based on spheres integrated with a waveguide for ultraprecise laser surgery. Our design is optimized for using a hollow-core microstructured fiber as a delivery system for a single-mode Er:YAG laser operating at l=2.94 micron. Using a high-index (n~1.7-1.9) microsphere as the focusing element we demonstrate experimentally the beam waist ~2l, which is sufficiently small for achieving ultraprecise surgery.

For embedded microspherical arrays, we developed a technology of incorporating high-index (n~1.9-2.1) spheres inside a thin-films made frompolydimethylsiloxane (PDMS). We showed that by using liquid lubrication, such thin-films can be translated along the surface to investigate structures and align different spheres with various objects. By using a rigorous resolution treatment, we demonstrated a resolution ~l/7 which can be obtained by such thin-films.


We experimentally demonstrated that microspheres integrated with mid-IR photodetectors produce a photocurrent enhancement up to 100 times over a broad range of wavelengths from 2 to 5 micron. This effect is explained by an increased power density produced by the photonic jet coupled to the active device layers through the photodetector mesas. The photocurrent gain provided by photonic jets is found to be in good agreement with the numerical modeling.

Link to full dissertation:

Current position:

Research Faculty at the Georgia Tech Research Institute's Advanced Concepts Laboratory

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