Optical properties of the square superlattice photonic crystal structure and optical invisibility cloaking

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Blair, John L.
Summers, Christopher J.
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The refraction properties of photonic crystal lattices offers methods to control the beam steering of light through use of non-linear dispersion contours. In this thesis new photonic crystal structures, such as the square and triangular superlattices, that provide novel refractive properties are analyzed. The property difference between rows in these structures is the hole radius Δr. The difference in hole sizes leads to observation of the superlattice effect, that is, a change in the refractive index Δn between opposite rows of holes. The index difference becomes a function of the size of the smaller r2 hole area or volume due to the addition of the higher index background material compared to the larger r1 holes. The difference in hole radii Δr = r1 - r2 is referred to as the static superlattice strength and is designated by the ratio of r2/r1. The superlattice strength increases as the ratio of r2/r1 decreases. The hole size modulation creates modified dispersion contours that can be used to fabricate advanced beam steering devices through the introduction of electro-optical materials and a controlled bias. A discussion of these superlattice structures and their optical properties will be covered, followed by both static and dynamic tunable device constructions utilizing these designs. Also, static tuning of the devices through the use of atomic layer deposition, as well as active tuning methods utilizing liquid crystal (LC) infiltration, sealed LC cells, and the addition of electro-optic material will be discussed. Also in this thesis we present designs to implement a simpler demonstration of cloaking, the carpet cloak, in which a curved reflective surface is compressed into a flat reflective surface, effectively shielding objects behind the curve from view with respect to the incoming radiation source. This approach eliminates the need for metallic resonant elements. These structures can now be fabricated using only high index dielectric materials by the use of electron beam lithography and standard cleanroom technologies. The design method, simulation analysis, device fabrication, and near field optical microscopy (NSOM) characterization results are presented for devices designed to operate in the 1400-1600nm wavelength range. Improvements to device performance by the deposition/infiltration of linear, and potentially non-linear optical materials, were investigated.
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