Dynamically tunable dielectric Huygens metasurfaces
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Description
Optical metamaterials have naturally followed the law of increasing miniaturization to yield unprecedented manipulation and control of light at the nanoscale, thus paving the way toward the realization of next-generation photonic devices. These devices, based on two-dimensional flat metasurfaces, are already proving to be more compact and efficient when compared to their traditional bulky counterparts. Most of the ongoing research in this field has focused on static functionality, where optical performance is fixed after fabrication and cannot be altered. Hence, the scope of possible exciting applications is limited to only passive performance. Taking advantage of the abundance of external stimuli around us, such as temperature, pressure, stress, strain, electric field, and light, active optical metasurfaces can be realized which expand the frontiers of realizable implementations of photon-matter interactions. This dissertation surveys different approaches toward obtaining dynamic reconfigurability in dielectric Huygens metasurface platforms. Dielectric Huygens metasurfaces have been demonstrated to show unique optical performance by supporting multipolar resonance modes which can be spectrally manipulated by changes in geometry, incidence angle, and refractive index. This creates a versatile platform to achieve multifunctional metasurfaces via various tuning methods. Also, the choice of dielectric materials over plasmonics is beneficial due to lower dissipative losses, excitation of multipolar resonances, and potential CMOS adaptability. This dissertation is split into four important chapters. Chapter 2 discusses the prototyping of a custom-built sensor for refractive index measurement and biomarker detection. By tuning the refractive index of the capping fluid, the optical performance of the metasurface was altered, iii enabling the full characterization of the bulk fluid. This same approach was used to characterize culture filtrate peptide (CFP-10), a prominent tuberculosis biomarker that yielded different optical responses for different concentrations. Chapter 3 studies a well-known phase transition material, vanadium dioxide (VO2), whose optical performance is altered from semiconducting properties to metallic properties above its transition temperature (68oC). Changing the refractive index of resonant VO2 nanostructures leads to decoupled phase modulation and amplitude modulation at different wavelengths. Chapter 4 investigates mutual coupling in nanoantenna arrays. A figure of merit is proposed for estimating the nearest neighbor crosstalk in these systems. To experimentally verify this, three silicon-based Huygens beam deflectors were designed and fabricated. Chapter 5 shows efforts toward achieving highly efficient tunable metasurface holograms. A phase map is generated from the original intensity map using the Gerchberg-Saxton algorithm. The triangulation method for obtaining a nanoantenna-phase map is proposed and tested for three-point emitters whose amplitude and phase information are known. In summary, we examine the exciting physics of tunable dielectric Huygens metasurfaces and engineer them to realize fascinating functionality in diverse applications.