Fabrication of High Performance Metasurfaces by Nanoimprinting of Refractive Index

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This grant supports manufacturing research that advances knowledge pertaining to the fabrication of optical devices, an effort which promotes scientific progress in emerging technologies with the potential to advance national health, prosperity, and defense. Specifically, this research advances key capabilities in cost-effective nanomanufacturing of components known as metasurfaces, which can be tailored to manipulate light with almost arbitrary wavefront shaping control. This important technology holds relevance in areas such as biomedical imaging, optical communications, laser imaging detection and ranging, and optical management for laser trapping and solar energy applications. Nearly all currently available manufacturing processes for producing metasurfaces rely on structuring optical materials through patterning followed by material etching or deposition. This general approach faces fundamental limitations which impact metasurface performance, manufacturing yield, and scalability. This project conducts fundamental research that investigates an innovative fabrication pathway wherein a material's optical properties are directly manipulated and patterned at high resolution without any deposition or etching. In addition to supporting the fabrication of existing metasurface architectures this approach uniquely enables new metasurface designs offering superior operating bandwidths and fabrication tolerances. This award supports training of skilled workers to enter into science, technology, engineering, and math careers, provides support for research experiences at the undergraduate level, offers opportunities to integrate research within the undergraduate classroom, encourages women and underrepresented minorities and supports local outreach activities which fosters interest in science for K-12 students.The technical scope of this work includes: (a) developing a method for patterning refractive index on the surface of a chip with nanoscale resolution, (b) mapping the morphological tuning of porous nanomaterials to effective optical properties, (c) demonstrating the straight-forward fabrication of high performance metasurfaces with both binary and arbitrary refractive index profiles, and (d) offering a transformative new approach for non-resonant (broadband) phase control which overcomes interparticle spacing limitations and improves fabrication tolerance. This research focuses on a technique wherein porous substrates are locally imprinted and densified at high resolution by direct imprinting with three-dimensionally mastered stamps then planarized. With the aim of developing this nanomanufacturing approach to enable the cost effective fabrication of high performance metasurfaces, this research addresses key questions regarding process parameters, process variation and control, mechanical integrity, optical quality, and process limitations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.