Porous Silicon Gradient Refractive Index Micro-Optics

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The emergence and growth of transformation optics over the past decade has revitalized interest in how a gradient refractive index (GRIN) can be used to control light propagation. Two-dimensional demonstrations with lithographically defined silicon (Si) have displayed the power of GRIN optics and also represent a promising opportunity for integrating compact optical elements within Si photonic integrated circuits. Here, we demonstrate the fabrication of three-dimensional Si-based GRIN micro-optics through the shape-defined formation of porous Si (PSi). Conventional microfabrication creates Si square microcolumns (SMCs) that can be electrochemically etched into PSi elements with nanoscale porosity along the shape-defined etching pathway, which imparts the geometry with structural birefringence. Free-space characterization of the transmitted intensity distribution through a homogeneously etched PSi SMC exhibits polarization splitting behavior resembling that of dielectric metasurfaces that require considerably more laborious fabrication. Coupled birefringence/GRIN effects are studied by way of PSi SMCs etched with a linear (increasing from edge to center) GRIN profile. The transmitted intensity distribution shows polarization-selective focusing behavior with one polarization focused to a diffraction-limited spot and the orthogonal polarization focused into two laterally displaced foci. Optical thickness-based analysis readily predicts the experimentally observed phenomena, which strongly match finite-element electromagnetic simulations.
Publisher
AMER CHEMICAL SOC
Issue Date
2016-12
Language
English
Article Type
Article
Keywords

LUNEBURG LENS; TRANSFORMATION OPTICS; SUPERLATTICES; DIELECTRICS; LIGHT; CLOAK

Citation

NANO LETTERS, v.16, no.12, pp.7402 - 7407

ISSN
1530-6984
DOI
10.1021/acs.nanolett.6b02939
URI
http://hdl.handle.net/10203/224803
Appears in Collection
BiS-Journal Papers(저널논문)
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