2. Design

1
Design, Fabrication, and Characterization of
Nanophotonic DevicesScott 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
• with novel properties.
• Advance understanding of photonic band gap
  materials.
• Specifically, improve grating coupler
  efficiency.

• 3. Fabrication
• Electron Beam Lithography (EBL)
• Electron Beam Evaporation
• Reactive Ion Etching (RIE)
• Liquid Chemical Etching

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.

• Grating Coupler and Photonic Crystal Waveguide ?
• Material System Silicon on Insulator (SOI)
• upper cladding air
• core layer 228 nm Si
• lower cladding 700 nm SiO2
• low-loss single-mode waveguide for 1550 nm light

At right A grating couples light incident
from the air into a photonic crystal waveguide.
Mo
resist
426 nm
370 nm
Below RIE produces the Mo mask for the etching
of a photonic crystal lattice.
724 nm
resist
Si
345 nm
Mo
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.
426 nm
Si
Above A grating coupler mask is produced in
resist via EBL.

• 2. Design
• Determine grating coupler period from theory
• Determine photonic crystal lattice type and
  dimensions
• from simulations.

426 nm
242 nm
724 nm
426 nm
360 nm
360 nm
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/? ? 0.28, where a is the lattice
parameter and ? is the free space wavelength of
incident radiation.
Above The waveguide tapers to a narrow channel
the width of a single lattice row.
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/SiO2 interface.
Si
Air
1264 nm
360 nm
Air
992 nm
426 nm

• 4. Characterization
• Study grating coupler efficiency as a function
  of grating period and depth, laser wavelength,
• and angle of incidence.
• Analyze photonic band gap properties.
• Measure waveguide confinement and loss.

Si
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/? ? 0.84, where a
is the lattice parameter and ? is the free space
wavelength of incident radiation.
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.

• 5. Future Work
• Optimize coupling from planar to channel
  waveguides.
• Measure waveguide loss for sharp channel bends.
• Develop novel photonic band gap devices, such
  as high-selectivity tunable wavelength
• division multiplexers.