Joseph Neil Mait

This paper uses radio-frequency-over-fiber (RFoF), or RF-photonic links, to implement a remotely distributed antenna system that preserves both the spatial and temporal coherence of RF signals, over long distances with negligible propagation loss. The system is used to implement optimized complex weights, on distributed antenna elements, to realize “flat,” i.e., lying in the plane of propagation, holographic field profiles. Experimental validation of a one-dimensional indoor system is used to demonstrate such “in-plane” holograms along with their comparison to simulation results.

I present a model for an achromatic surface lens based on the superposition of lenses that focus discrete wavelengths independent of one another. The model potentially provides insight into the physical behavior of experimentally demonstrated lenses. It also suggests a simple design algorithm.

We use first-order optical principles to examine the ability of gradient index (GRIN) lenses to correct chromatic aberrations. We consider radial GRIN lenses with flat surfaces, with a flat diffractive surface, and with curved surfaces. We model the GRIN material system as a locally varying, subwavelength blend of three materials. In this model, we demonstrate that the color-correcting properties of each lens type can be expressed solely in terms of the dispersion properties of the base materials. We find, at this level of approximation, that the material condition for a two-material GRIN achromat with curved surfaces is identical to that for a homogeneous doublet achromat comprised of the same two materials. For the more general case of three-material, ternary GRIN elements, we use the theory to develop a figure-of-merit-based optimization approach. This allows us to identify promising material combinations without first fabricating a GRIN element. The optimization approach can be applied to alternate GRIN geometries and arbitrary glass catalogs. We use our model to search a large, commercial glass catalog to identify the best achromatic glass combinations for the three different GRIN lenses described above. Significant numerical effort was required to identify which glass combinations performed best. Ternary glass combinations are necessary to achieve good achromatic performance for flat geometries. Diffraction combined with a graded-index enables improved color correction for the same optical power or nearly a factor of two increase in power for the same level of color correction. Glass pairs that perform well as an achromatic doublet also perform well chromatically when blended in a GRIN singlet.

We review advances in Computational Imaging that have occurred since the mid-1990s. The advent of highly integrated platforms, such as the smartphone, has made the linkage between optics and processing intimate and natural. This review covers key technological developments and insights over the past two decades and examines current trends to predict future capabilities.

We review advances in Computational Imaging that have occurred since the mid-1990s. A similar review we presented more than a decade ago, "Old Wine in New Bottles?" gave a cautious assessment.

We introduce k-space tomography, the computational reconstruction of the electromagnetic environment. Our technique relies upon up-converting detected radio-frequency (RF) waves to optical frequencies and exploiting optical phase modulation and the dispersive properties of optical fibers to encode the k-vectors of the incident RF wavefield.

The U.S. Army Research Laboratory (ARL) is the premier laboratory for land forces in the United States. A young organization that in 2017 celebrates 25 years of discovery, innovation, and transition of science and technology, ARL has already contributed significantly to several disciplines in optical sciences.

We show that a gradient-index element designed from a blend of three materials allows a designer to specify independently the element’s refractive index and its change in refractive index with respect to wavelength. We show further the effectiveness of this approach by comparing modeled chromatic performance of deflectors consisting of a single material, a binary blend of materials, and a ternary blend.