Flexible Reflective Metasurface Displays

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

Abstract: Non-technical: The range of colors and hues in the natural world are amazing, but perhaps even more astonishing is the ability of certain species to actively mimic them. Though the specific mechanisms are as varied as the species, each has a set of color producing cells which can span the visible spectrum. Within this vast set of creatures, cephalopods/octopi stand out as champions, who are adept to cover vast swaths of color within milliseconds. The key aspect of these color displays in nature is generation of color on a thin, flexible and conformally mapped surface whereas our manmade state-of-the art displays still remained rigid, brittle and bulky in nature. It's with cephalopods in mind that a flexible reflective metasurface display is proposed in which each pixel can be actively tuned across the visible spectrum. The proposed work is important for the development of low cost reflective displays on flexible substrates. The newly developed printing techniques will enable large area printing of nanostructured metasurfaces for low cost manufacturing. The program provides a good platform for interdisciplinary research (including integrated optics, nanofabrication and materials science and engineering) and graduate education. The research will generate exciting scientific content for enriching the PI's graduate and undergraduate teaching. The program will integrate outreach activities that span autistic students, K-12 students and other underrepresented minorities. Technical: The main focus of the proposed work is to develop an angle independent reflective metasurface with liquid crystals to achieve dynamic color tuning pixels. The implementation of dynamic pixels will reduce the need for multiple colored subpixels, thereby eliminating layered processing steps, increasing resolution, and allow unrivaled color control. Furthermore, the device will independently tune color and grey-scale within a singular liquid crystal cell through novel liquid crystal optics design and multiple electrodes. Using nanoimprint lithography to produce the plasmonic structure over large areas, one can bypass expensive and tedious electron-beam or deep-UV lithography techniques used in fabricating many previously reported plasmonic devices. This in combination with ultrafast direct laser writing, multiple features at varying size scales can be incorporated into the master patterns. A single device master can include arbitrarily pixelated plasmonic metasurface, microscopic liquid crystal cell spacers, and nanoscale liquid crystal alignment gratings. One such master can produce 100's of polymeric imprinting stamps, and one such stamp can produce 1000's of imprints without any noticeable pattern degradation. Nanoimprint lithography has also been translated to roll-to-roll processing which shows the entire fabrication process can be scaled to factory norms. There is much to understand and develop in the field of actively tunable plasmonics. A fast response, angle independent liquid crystal-metasurface based display which can actively shift the color of its pixels is achievable based on this interdisciplinary research. An in depth analysis of the plasmonic metasurface, liquid crystal orientation and how they influence each other will be studied. A key objective of the proposed system is to design a wide angle metasurface based on a specially engineered metal-insulator-metal Fabry-Perot plasmon resonance which doesn't depend on structure periodicity. While apt at producing color, these plasmonic surfaces cannot produce deep black states needed for displays due to intrinsic narrow band absorption. The proposed work intends to integrate plasmonic color tuning and liquid crystal grey state polarimetry within the same liquid crystal cell. By introducing two sets of electrodes, color and brightness can be independently tuned through a novel device design. The proposed device can readily be fabricated on flexible substrates as the low temperature fabrication process is compatible with low glassing temperature plastics. Special metasurface patterning allows device flexibility without damage to the underlying nanopatterns. Such an approach can not only lead to large area skin-like full color display elements, but can also improve the active tunability of general plasmonic metamaterial systems.