Abstract
We investigate the near-field focusing properties of three-dimensional phase antennas consisting of concentric rings designed to have source and image spots separated by several microns from the lens. Tight focal spots are obtained for silicon or gold rings patterned in a silica matrix. We analyze in detail the dependence of the performance of these lenses on geometrical parameters such as the number of rings, the ring thickness, and the focal distance. Subwavelength focal spots are found to form at distances of tens of wavelengths from the lens, thus suggesting applications to remote sensing and penlight microscopy and lithography.
Highlights
The ability to focus light within tiny spaces is important for applications as diverse as molecule sensing [1] and signal processing [2]
We investigate the near-field focusing properties of threedimensional phase antennas consisting of concentric rings designed to have source and image spots separated by several microns from the lens
We have studied for simplicity the symmetric case, with both source and image spots positioned in the same host material, these concepts can be generalized to lenses with two different focal distances, a1 and a2, in an asymmetric environment of dielectrics with indices n1 and n2, leading to ring radii bi satisfying the equation n1 a21 + b2i + n2 a22 + b2i = iλ0
Summary
The ability to focus light within tiny spaces is important for applications as diverse as molecule sensing [1] and signal processing [2]. The constructive interference of light transmitted through slits of varying width [6, 12, 15] and quasi-crystalline distributions of holes [7] has been used to produce near-field focusing of a plane wave This principle has been recently employed to demonstrate optical tweezing using a Fresnel zone plate [11]. We present a three-dimensional implementation of a near-field lens that is designed to focus a point source on an image spot separated by several wavelengths. This type of design is related to Fresnel lenses, which. We conclude with a brief discussion of possible applications of near-field lenses
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