Life at Low Reynolds Number

Objects driven through periodically modulated potential-energy landscapes in two dimensions can become locked in to symmetry-selected directions that are independent of the driving force's orientation. We investigate this problem in the overdamped limit, and demonstrate that the crossover from free-flowing to locked-in transport can depend exponentially on an object's size, with this exceptional selectivity emerging from the periodicity of the environment.

Transport and Fractionation in Periodic Potential-Energy Landscapes

In recent years, the emergence of a new type of sub-wavelength dielectric
grating with a high refractive index contrast, typically referred to as high contrast grating, and its simple fabrication procedure have given rise to numerous applications in integrated photonics and optoelectronics. The on-going demand for miniaturised planar devices in the near-infrared spectral range and the compatibility with standard processing techniques motivated us to explore the intriguing resonance effects in high contrast gratings for the application as broadband mirrors, reflective lenses, and as part of static and tuneable Fabry-Perot cavities.
We chose amorphous silicon as the high refractive index material. The characteristics of grating mirrors were analysed numerically and measured experimentally, confirming their suitability for use as focussing reflectors and cavity mirrors in a Fabry-Perot interferometer. As a result, a new type of reflective diffractive lens incorporating multiple phase jumps was designed, fabricated, and experimentally tested, and showed improved performance in terms of numerical aperture compared to other devices in the literature. Furthermore, initial experiments by integrating arrays of such lenses with a microfluidic platform showed an application potential in the area of large-scale optical trapping. In an attempt to develop functional wavelength-selective filters utilising high contrast gratings and microelectromechanical systems, we investigated static cavities based on metals and gratings, which included simulation, development of the fabrication process, and optical characterisation. Following these proof-of-principle studies and the computational analysis of the mechanical behaviour of flexible membrane designs, the challenge in making tuneable devices was to fabricate a fully working tuneable filter and its characterisation.
Overall, this thesis contributes to the field of integrated and planar silicon photonics by addressing the design and the performance aspects of high contrast grating lenses with high numerical aperture as well as addressing key challenges in the fabrication of tuneable filters.

Planar optics with wavelength-scale high contrast gratings

DR. WILEY remarks that his book “is not written for the scientific investigator, but for the average, sober-minded, reasonably well-educated American citizen.” A general account of the beverages discussed is, in fact, what is given, neither severely technical nor flimsily “popular.” The facts are stated carefully, as would be expected from the author, but little or no scientific knowledge on the part of the reader is assumed. Beverages and their Adulteration. Origin, Composition, Manufacture, Natural, Artificial, Fermented, Distilled, Alkaloidal, and Fruit Juices. By Dr. Harvey W. Wilcy. Pp. xv + 421 + n plates. (London: J. and A. Churchill, 1919.) Price 21s. net.

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Beverages and their Adulteration Origin, Composition, Manufacture, Natural, Artificial, Fermented, Distilled, Alkaloidal, and Fruit Juices

We report the high speed scanning submicronic microscopy (SSM) using a low cost polymer microlens integrated at the extremity of an optical fiber.These microlenses are fabricated by a free-radical photopolymerization method.Using a polymer microlens with a radius of curvature of 250 nm,a sub-micrometric gold pattern is imaged experimentally by SSM.Different distances between the tip and the sample are used with a high scanning speed of 200 cm/s.In particular,metallic absorption contrasts are described with an optical spatial resolution of 250 nm at the wavelength of 532 nm.Moreover,finite-difference time-domain (FDTD) simulations concerning the focal lengths of microlenses with different geometries and heights support the experimental data.

High speed sub-micrometric microscopy using optical polymer microlens

......................................... . .......................................................................... iv Declaration ....................................... ............................................................................. v Acknowledgements ................................................................................................ vi Publications ...................................... .......................................................................... viii Peer reviewed journals ............................ ............................................................. viii Book Chapter ................................................................................................... ix Patents .............................................................................................................. ix Conference Publications ........................... ............................................................. ix List of Abbreviations ............................. ...................................................................... xi Table of

Praveen Cheriyan Ashok

Papers

Integration methods for enhanced trapping and spectroscopy in optofluidics