Silicon photonics is a mature technology with many foundries worldwide. Photonic integrated circuits (PICs) are mass manufactured by patterning devices on the surface of the silicon wafer. Although great circuit functionality can be achieved, the architecture is limited to two-dimensional binary structures with fixed refractive index contrast. Recently, in collaboration with the research groups of Paul Braun and Kimani Toussaint at the University of Illinois, we developed a new three-dimensional direct laser writing technique called Subsurface Controllable Refractive Index via Beam Exposure (SCRIBE). This lithographic approach enables submicron control of the local refractive index over a continuous range of greater than 0.3 by controlling the fill fraction of photoresist inside nanoporous silicon and silica scaffolds. Utilizing SCRIBE’s unprecedented index range and 3D writing accuracy, we demonstrated novel volumetric micro-optic and photonic elements including 3D waveguides and microring resonators, compound achromatic lenses, planar axicons, photonic nanojet generators, variable-color distributed Bragg reflectors, and the world’s smallest (15 µm diameter) spherical Luneburg lens. In this talk, I will explain the method, present device results, and discuss some potential applications enabled by this paradigm shifting architecture.

Dr. Lynford Goddard received his Ph.D. in physics from Stanford in 2005. His thesis topic was 1.5-micron gallium arsenide-based lasers. He conducted postdoctoral research at Lawrence Livermore National Lab on photonic integrated circuits and sensors. He is a Professor of Electrical and Computer Engineering and the Founding Director of the Institute for Inclusion, Diversity, Equity, and Access in the Grainger College of Engineering at the University of Illinois. His research group fabricates, tests, and models photonic sensors, circuits, and instrumentation, develops novel device processing techniques, and applies quantitative phase microscopy for nanoscale science and for semiconductor wafer metrology. He received the PECASE award from President Obama and the Early Career Public Engagement Award from AAAS. He is a Fellow of SPIE and of OSA and co-author of over 200 publications and has 13 issued patents.