Collaborative Research: Nanopatterning and temporal control of phase-change materials for reconfigurable photonics

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The ability to control light dynamically, commonly known as reconfigurable photonics, is ubiquitous in everyday life with diverse and varied applications ranging from supermarket barcode readers to adaptive optics for deep-space telescopes, and from dynamic theatre lighting to medical microscopy. Currently, these applications rely on spatial light modulator (SLM) technologies that have significant limits: They are slow, costly, involve fragile moving parts, and not versatile enough to adapt to modern challenges. In this project, a material known as phase-change materials (PCMs) is used to create a faster and less costly spatial light modulator. This is done by combining a type of PCM that is commonly used in Blu-Ray discs, known as GST, with new types of nanofabrication and electronic control to create advanced reconfigurable photonic devices with performance metrics that far exceed what is currently available. The benefits of this project are three fold. At the core, this project falls at the intersection between two fields of research: nanoscale thermal science, and photonics. This will lead to an advancement of both fields in a new and unexplored dimension. On the education front, the project will allow for student exchanges between the University of Dayton and Stanford University, for the first time. It will also bolster the relationship with minority-serving institutes. The longer term impact of this work will be to provide a stepping stone towards providing compact, high speed, low power consumption devices, manufactured using inexpensive fabrication methods for use in technologies based on reconfigurable photonics. Current state-of-the art in light modulation for reconfigurable photonic applications relies on spatial light phase modulation via liquid-crystal on silicon (LCoS) or Microelectromechanical (MEMS) systems, both of which have major limitations. One current hurdle is the speed at which these devices operates, and the other is the complexity and low-yield of their fabrication process. The goal of this research is to use phase-change materials (PCMs) for coherent spatial and temporal control of light in a lossless, high-speed manner, well beyond the performance of standard liquid crystal and MEMs devices today. PCMs alter their optical properties (refractive index) through a controlled crystalline-to-amorphous phase transition, making them ideal for light modulation applications. However, two problems persist with PCMs: a) The phase transition is slow and b) the phase transition is binary (on/off), preventing the implementation of the necessary phase modulation devices. This proposal looks at both these problems and presents a novel and unified solution based on nanopatterning and temporal control of the phase-change process. Through the use of a new and scalable technique for self-assembled patterning, we alter the temperature dynamics and increase the speed of the phase-change by orders of magnitude. By using temporally-controlled electric stimulus, it is possible to achieve true continuous phase modulation of light overcoming the binary nature of the material itself. Phase-change materials, which naturally lend themselves to mass manufacturing, have the potential to alter the area of reconfigurable photonics and light modulation devices provided their full potential is exploited. This project aims to achieve that potential through a new collaboration between fields of engineering that typically do not see much overlap. Ultimately, the goal is to implement basic spatial light modulation devices, with unique engineered thermal properties, which presents a new cross-pollination of these fields, which could lead to further developments in both areas of science.