2. Design2. Design Determine grating coupler period from theory: Determine grating coupler period from theory:

Determine photonic crystal lattice type and dimensionsDetermine photonic crystal lattice type and dimensions

from simulations.from simulations.

Design, Fabrication, and Characterization of Nanophotonic DevicesDesign, Fabrication, and Characterization of Nanophotonic DevicesScott A. MasturzoScott A. Masturzo and Joseph T. Boyd and Joseph T. Boyd

Department of Electrical and Computer Engineering and Computer Science, University of CincinnatiDepartment of Electrical and Computer Engineering and Computer Science, University of CincinnatiHoward E. Jackson, Department of Physics, University of CincinnatiHoward E. Jackson, Department of Physics, University of Cincinnati

Jan Yarrison-Rice, Department of Physics, Miami UniversityJan Yarrison-Rice, Department of Physics, Miami University

1. Motivation1. Motivation Integrate photonics with electronics and optoelectronics for faster and more efficient devicesIntegrate 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.

sin

en

At right:At right: A grating A grating couples couples light light incident incident from the air from the air into a into a photonic photonic crystal crystal waveguide.waveguide.

Grating Coupler and Photonic Crystal WaveguideGrating Coupler and Photonic Crystal Waveguide → →

Material System: Silicon on Insulator (SOI)Material System: Silicon on Insulator (SOI)upper cladding – air upper cladding – air core layer – 228 nm core layer – 228 nm SiSilower cladding – 700 nm lower cladding – 700 nm SiOSiO22

low-loss single-mode waveguide for 1550 nm lightlow-loss single-mode waveguide for 1550 nm light

Below:Below: Laser light is directed at a variable incident angle Laser light is directed at a variable incident angle onto a grating coupler on the surface of an SOI wafer. onto a grating coupler on the surface of an SOI wafer. Light exiting the cleaved edge of the wafer is scattered Light exiting the cleaved edge of the wafer is scattered upward into a vertical microscope column.upward into a vertical microscope column.

Above:Above: The incident angle is varied about 45° The incident angle is varied about 45° for two gratings of different depths and periods of for two gratings of different depths and periods of 724 nm.724 nm.

3. Fabrication3. Fabrication Electron Beam Lithography (EBL)Electron Beam Lithography (EBL) Electron Beam EvaporationElectron Beam Evaporation Reactive Ion Etching (RIE)Reactive Ion Etching (RIE) Liquid Chemical EtchingLiquid Chemical Etching

4. Characterization4. 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.

0

0.2

0.4

0.6

0.8

1

42 43 44 45 46 47 48

Angle of Incidence (degrees)

Nor

mal

ized

Cou

plin

g E

ffic

ien

cy i

grating depth ~ 60 nm

grating depth ~ 90 nm

5. Future Work5. 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 wavelengthDevelop novel photonic band gap devices, such as high-selectivity tunable wavelength

division multiplexers.division multiplexers.

SiSi

AirAir992 nm992 nm

1264 nm1264 nm

Above:Above: Simulations predict that this 2-D hexagonal lattice of Simulations predict that this 2-D hexagonal lattice of circular air holes in circular air holes in SiSi yields a photonic energy band diagram with a yields a photonic energy band diagram with a photonic band gap at photonic band gap at 0.79 0.79 ≲ a/≲ a/λλ ≲ 0.84 ≲ 0.84, where , where aa is the lattice is the lattice parameter and parameter and λλ is the free space wavelength of incident is the free space wavelength of incident radiation.radiation.

Below:Below: Simulations predict that this 2-D square lattice of Simulations predict that this 2-D square lattice of circular air holes in circular air holes in SiSi yields a photonic energy band diagram yields a photonic energy band diagram with a photonic band gap at with a photonic band gap at 0.27 0.27 ≲ a/≲ a/λλ ≲ 0.28 ≲ 0.28, where , where aa is is the lattice parameter and the lattice parameter and λλ is the free space is the free space wavelength of incident radiation.wavelength of incident radiation.

SiSi

AirAir

360 nm360 nm

426 nm426 nm

period grating

radiation incident of h wavelengtspace free

waveguideof index refractive effective en

incidence of angle

The nanoscale dimensions of the gratings and photonic crystal lattices The nanoscale dimensions of the gratings and photonic crystal lattices call for EBL and RIE. The shallow etch depth of the grating allows for 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 the direct use of resist as an etch mask, while the deeper lattices require an intermediate metal masking step.require an intermediate metal masking step.

Above:Above: A grating coupler mask is produced in A grating coupler mask is produced in resist via EBL.resist via EBL.

Above:Above: A thin (~ 30 nm) layer of A thin (~ 30 nm) layer of MoMo is is deposited on the SOI surface before spin deposited on the SOI surface before spin coating with resist for the EBL of a photonic coating with resist for the EBL of a photonic crystal lattice pattern.crystal lattice pattern.

Below:Below: RIE produces the RIE produces the MoMo mask for the mask for the etching of a photonic crystal lattice.etching of a photonic crystal lattice.

724 nm724 nm

426 nm426 nm

345 nm345 nm

426 nm426 nm

370 nm370 nm

Above:Above: The grating is etched to a depth of less than The grating is etched to a depth of less than 100 nm into the 100 nm into the SiSi surface, while the photonic crystal surface, while the photonic crystal lattice is etched through all 228 nm of lattice is etched through all 228 nm of SiSi to the to the Si/SiOSi/SiO22 interface. interface.

Above:Above: The waveguide tapers to a narrow channel The waveguide tapers to a narrow channel the width of a single lattice row.the width of a single lattice row.

724 nm724 nm 426 nm426 nm

360 nm360 nm

242 nm242 nm

360 nm360 nm

426 nm426 nm

MoMo resistresist

SiSi

MoMo SiSi

resistresist