@article{8cf289dd97f145f7911c2f8b214a1aa5,
title = "Electrochemical Fabrication of Flat, Polymer-Embedded Porous Silicon 1D Gradient Refractive Index Microlens Arrays",
abstract = "Gradient refractive index (GRIN) optics has attracted considerable interest due to the ability to decouple optical performance from optical element shape. However, despite the utility of GRIN optical components, it remains challenging to fabricate arbitrary GRIN profiles and the available refractive index contrast remains small, particularly at the microscale. Here, using mathematical transformations that the authors developed, the electrochemical waveform required to electrochemically etch arrays of bulk Si microstructures into 1D porous Si (PSi) GRIN microlens arrays (MLAs) is determined. This waveform is then used to form high refractive index contrast MLAs containing precisely-defined, arbitrary refractive index profiles. The MLAs are then embedded in a transparent optical polymer, mechanically detached from the host Si substrate, and planarized via simple polishing. Cylindrical microlenses and 1D axicons are demonstrated and characterized, and the optical behavior is found to be in agreement with theory. These MLAs could find applications in displays, photodetectors, and optical microscopy.",
keywords = "axicons, bessel beams, birefringence, flat optics, micro-optics",
author = "Krueger, {Neil A.} and Holsteen, {Aaron L.} and Qiujie Zhao and Kang, {Seung Kyun} and Ocier, {Christian R.} and Weijun Zhou and Glennys Mensing and Rogers, {John A} and Brongersma, {Mark L.} and Braun, {Paul V.}",
note = "Funding Information: This work was supported by the U.S. Department of Energy “Light-Material Interactions in Energy Conversion” Energy Frontier Research Center under grant DE-SC0001293 (experimental studies) and the Dow Chemical Company (etch model development). This research was also conducted with Government support under and awarded by DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a (N.A.K. and A.H.). This research was carried out in part in the Fabrication Facility and Center for Microanalysis of Materials at the Materials Research Laboratory, the Microscopy Suite and Visualization Laboratory at the Beckman Institute, the Micro and Nanotechnology Laboratory, and the Micro-Nano-Mechanical Systems Cleanroom at the University of Illinois. The authors acknowledge Dr. Thomas R. O{\textquoteright}Brien, Dr. Hailong Ning, Dr. Hao Chen, and Dr. Julio Soares for helpful suggestions regarding optical simulation and characterization, as well as Kaitlin Tyler and Tara Cullerton for assistance with planarization. Funding Information: This work was supported by the U.S. Department of Energy ?Light-Material Interactions in Energy Conversion? Energy Frontier Research Center under grant DE-SC0001293 (experimental studies) and the Dow Chemical Company (etch model development). This research was also conducted with Government support under and awarded by DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a (N.A.K. and A.H.). This research was carried out in part in the Fabrication Facility and Center for Microanalysis of Materials at the Materials Research Laboratory, the Microscopy Suite and Visualization Laboratory at the Beckman Institute, the Micro and Nanotechnology Laboratory, and the Micro-Nano-Mechanical Systems Cleanroom at the University of Illinois. The authors acknowledge Dr. Thomas R. O'Brien, Dr. Hailong Ning, Dr. Hao Chen, and Dr. Julio Soares for helpful suggestions regarding optical simulation and characterization, as well as Kaitlin Tyler and Tara Cullerton for assistance with planarization. Publisher Copyright: {\textcopyright} 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim",
year = "2018",
month = jul,
day = "11",
doi = "10.1002/pssa.201800088",
language = "English (US)",
volume = "215",
journal = "Physica Status Solidi (A) Applications and Materials Science",
issn = "1862-6300",
publisher = "Wiley-VCH Verlag",
number = "13",
}