2. Design Determine grating coupler period from theory: Determine grating coupler period from theory: Determine photonic crystal lattice type and dimensions Determine photonic crystal lattice type and dimensions from simulations. from simulations. Design, Fabrication, and Characterization of Nanophotonic Devices Scott A. Masturzo and Joseph T. Boyd Department of Electrical and Computer Engineering and Computer Science, University of Cincinnati Howard E. Jackson, Department of Physics, University of Cincinnati Jan Yarrison-Rice, Department of Physics, Miami University 1. Motivation Integrate photonics with electronics and optoelectronics for faster and more efficient devices Integrate photonics with electronics and optoelectronics for faster and more efficient devices with novel properties. with novel properties. Advance understanding of photonic band gap materials. Advance understanding of photonic band gap materials. Specifically, improve grating coupler efficiency. Specifically, improve grating coupler efficiency. At right: A grating couples light incident from the air into a photonic crystal waveguide. Grating Coupler and Photonic Crystal Waveguide → Material System: Silicon on Insulator (SOI) upper cladding – air core layer – 228 nm Si lower cladding – 700 nm SiO 2 low-loss single-mode waveguide for 1550 nm light low-loss single-mode waveguide for 1550 nm light Below: Laser light is directed at a variable incident angle onto a grating coupler on the surface of an SOI wafer. Light exiting the cleaved edge of the wafer is scattered upward into a vertical microscope column. Above: The incident angle is varied about 45° for two gratings of different depths and periods of 724 nm. 3. Fabrication Electron Beam Lithography (EBL) Electron Beam Lithography (EBL) Electron Beam Evaporation Electron Beam Evaporation Reactive Ion Etching (RIE) Reactive Ion Etching (RIE) Liquid Chemical Etching Liquid Chemical Etching 4. Characterization Study grating coupler efficiency as a function of grating period and depth, laser wavelength, Study grating coupler efficiency as a function of grating period and depth, laser wavelength, and angle of incidence. and angle of incidence. Analyze photonic band gap properties. Analyze photonic band gap properties. Measure waveguide confinement and loss. Measure waveguide confinement and loss. 5. Future Work Optimize coupling from planar to channel waveguides. Optimize coupling from planar to channel waveguides. Measure waveguide loss for sharp channel bends. Measure waveguide loss for sharp channel bends. Develop novel photonic band gap devices, such as high-selectivity tunable wavelength Develop novel photonic band gap devices, such as high-selectivity tunable wavelength division multiplexers. division multiplexers. Si Air 992 nm 1264 nm Above: Simulations predict that this 2-D hexagonal lattice of circular air holes in Si yields a photonic energy band diagram with a photonic band gap at 0.79 ≲ a/λ ≲ 0.84, where a is the lattice parameter and λ is the free space wavelength of incident radiation. Below: Simulations predict that this 2-D square lattice of circular air holes in Si yields a photonic energy band diagram with a photonic band gap at 0.27 ≲ a/λ ≲ 0.28, where a is the lattice parameter and λ is the free space wavelength of incident radiation. Si Air 360 nm 426 nm The nanoscale dimensions of the gratings and photonic crystal lattices call for EBL and RIE. The shallow etch depth of the grating allows for the direct use of resist as an etch mask, while the deeper lattices require an intermediate metal masking step. Above: A grating coupler mask is produced in resist via EBL. Above: A thin (~ 30 nm) layer of Mo is deposited on the SOI surface before spin coating with resist for the EBL of a photonic crystal lattice pattern. Below: RIE produces the Mo mask for the etching of a photonic crystal lattice. 724 nm 426 nm 345 nm 426 nm 370 nm Above: The grating is etched to a depth of less than 100 nm into the Si surface, while the photonic crystal lattice is etched through all 228 nm of Si to the Si/SiO 2 interface. Above: The waveguide tapers to a narrow channel the width of a single lattice row. 724 nm 426 nm 360 nm 242 nm 360 nm 426 nm Moresist Si Mo Si resist