Phase Shaping In The Infrared By Planar Quasi-periodic Surfaces Comprised Of Sub-wavelength Elements

Reflectarrays are passive quasi-periodic sub-wavelength antenna arrays designed for discrete reflected phase manipulation at each individual antenna element making up the array. By spatially varying the phase response of the antenna array, reflectarrays allow a planar surface to impress a non-planar phasefront upon re-radiation. Such devices have become commonplace at radio frequencies. In this dissertation, they are demonstrated in the infrared for the first time--at frequencies as high as 194 THz. Relevant aspects of computational electromagnetic modeling are explored, to yield design procedures optimized for these high frequencies. Modeling is also utilized to demonstrate the phase response of a generalized metallic patch resonator in terms of its dependence on element dimensions, surrounding materials, angle of incidence, and frequency. The impact of realistic dispersion of the real and imaginary parts of the metallic permittivity on the magnitude and bandwidth of the resonance behavior is thoroughly investigated. Several single-phase reflectarrays are fabricated and measurement techniques are developed for evaluating these surfaces. In all of these cases, there is excellent agreement between the computational model results and the measured device characteristics. With accurate modeling and measurement, it is possible to proceed to explore some specific device architectures appropriate for focusing reflectarrays, including binary-phase and phase-incremental approaches. Image quality aspects of these focusing reflectarrays are considered from geometrical and chromatic-aberration perspectives. The dissertation concludes by briefly considering two additional analogous devices--the transmitarray for tailoring transmissive phase response, and the emitarray for angular control of thermally emitted radiation

Demonstrating Reflectarray Behavior At Infrared

Reflectarrays are traditionally passive, planar microstrip antenna devices designed for reflected phase manipulation at each individual antenna element making up the array. By varying the phase response across the surface with the antenna elements, reflectarrays allows a planar surface to exhibit electromagnetically an arbitrary geometry, such as a spherical surface. Initially proposed as a low-cost replacement for bulky parabolic reflectors, reflectarrays have been successfully developed and utilized at both RF and millimeter-wave frequencies. From the standpoint of an optical systems designer, adapting low-frequency reflectarray technology to develop a sub-millimeter and infrared reflectarray (SMIR) would provide a highly desirable alternative to similarly behaved polished or diffractive optical devices. Compared to traditional optical reflectors, SMIRs should be cheaper to fabricate, have a smaller physical footprint, allow for utility stacking, and encourage direct integration of aberration correction. To demonstrate the feasibility of utilizing reflectarray technology at infrared (IR), a simple SMIR proof of concept has been successfully designed, fabricated, and tested. The SMIR is comprised of three independent arrays or stripes of a single size element on a coated optical flat. Actual reflectarray elements consist of variable size patches that exhibit higher operating bandwidths than reflectarrays utilizing other types of elements and are easier to fabricate at small dimensions. For testing, each stripe element has been chosen to exhibit a unique phase shift for measurement using an IR interferometer. Preliminary investigation of future reflectarray development is also discussed. Emphasis is placed on improving operating bandwidth, development of a planar focusing element, and aberration correction. With further development, SMIR technology should present a powerful tool for low cost, flexible optical system design