NOVEL OPTICAL METAMATERIALS, ABSORBERS, AND FILTERS BASED ON PERIODIC NANOSTRUCTURES

Open Access
Author:
Yun, Seokho
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 20, 2011
Committee Members:
  • Theresa Stellwag Mayer, Dissertation Advisor
  • Theresa Stellwag Mayer, Committee Chair
  • Douglas Henry Werner, Committee Member
  • Zhiwen Liu, Committee Member
  • Vincent Henry Crespi, Committee Member
Keywords:
  • optical filters
  • photonic crystals
  • absorbers
  • metamaterials
Abstract:
This research describes the design, fabrication, and characterization of novel optical metamaterials, absorbers, and filters based on periodic all-dielectric and metallo-dielectric nanostructures. With a properly chosen optical structure and its constituent materials, the geometry and dimensions were optimized to satisfy the user-specified criteria using a robust genetic algorithm. First, planar all-dielectric nanostructures were exploited to synthesize a mid-infrared (IR) filter and a mirror. An array of doubly periodic amorphous silicon (a-Si) blocks induced a guided mode resonance, resulting in a polarization insensitive and incidence angle tolerant single stop band at 3.0 µm. An effective medium approach was also applied to this planar all-dielectric nanostructure to produce a high efficiency mid-IR mirror centered at 3.3 µm. The fabricated filter and mirror structures were characterized using Fourier transform infrared (FTIR) spectroscopy to show excellent agreement with the predicted responses. Secondly, metallo-dielectric nanostructures were investigated to realize a zero index metamaterial (ZIM), a dispersion engineered metamaterial filter, and a metamaterial absorber. A free-standing optical ZIM, consisting of a gold-polyimide-gold tri-layer stack perforated by air holes, was synthesized at 1.55 µm with low absorption loss and a good impedance match to free space, verified through characterization using spectral holography. Based on the similar structure with minor modifications, a dispersion engineered broad band filter was demonstrated in the mid-IR wavelength range of 3-3.5 µm with a suppressed group delay. A conformal metamaterial absorber, patterned on a flexible polyimide and gold thin film stack, was also synthesized with a narrow band, polarization independent, incidence angle tolerant absorptivity centered at mid-IR wavelengths of 3.3 µm and 3.9 µm. The performance of the fabricated metamaterial filter and absorber was verified using FTIR, exhibiting excellent agreement with the simulated values.