Transcript Three Dimensional Photonic Crystals

Three Dimensional Photonic
Crystals
Corey Ulmer
Outline
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What are Photonic Crystals/Why Important?
How They Work
Manufacturing Challenges
Manufacturing Techniques
– Layer by layer techs.
– Serial tech.
– Mass production tech.
• Conclusions
Image from S. G. Johnson et al., Nature. 429, 538
(2004)
SEM Micrograph of
a photonic crystal
made with a layer
by layer E-Beam
lithography
technique
What Are They?
Electron band gap in semiconductor
Photon band gap in photonic crystal
• Photonic crystals analogous to semiconductors
• Crystal structure gives rise to band gap
• Photons inside band gap reflect off material
Images from http://www.doitpoms.ac.uk/tlplib/semiconductors/printall.php and modified from http://abinitio.mit.edu/photons/tutorial/ lecture 3
Why Do They Matter?
• Used in
– Lossless reflective coatings on
mirrors/lenses
– Iridescent paint
– Low threshold laser diode
SEM Micrograph of photonic
crystal fiber cross section
Paint makes use of photonic crystals
• Potential Uses
– Replace fiber optic cable – higher
energy light, different wavelengths
– Optical computers – theoretically can be
thousands of times faster than electronic
computers
Images from http://www.landrover.co.uk/gb/en/Vehicles/New_Range_Rover/Autobiography/exterior_features.htm
and http://www.cns.cornell.edu/NanoPhotonics05Gaeta.html
How Does it Work?
• Alternating dielectrics – high contrast
• Repeating periodic structure gives rise to forbidden zones
• Band gap size dependent primarily on a diff in dielectric constant, frequency
dependent primarily on cell size
• Example here is 1D (layers) – 1D always has a complete band gap (gap
covers all phase, k)
Image modified from http://www.icmm.csic.es/cefe/pbgs.htm
How Does it Work?
Rough schematic of 1, 2, and 3
dimensional photonic crystals. 1D very
easy – already has widespread application.
2D moderately difficult. 3D very hard.
• In 3D, allowed energies MUCH more
complicated
• Not all geometries have complete
band gap (does not block in all
directions)
Energy structure for 3D system
• However! If all it does is block light,
it’s not useful
• Intentional defects allow control of
light – waveguides, logic gates
Image from http://ab-initio.mit.edu/photons/tutorial/ lecture 2
Manufacturing Challenges
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Technique must produce repeating structure accurately
Must be able to introduce controlled defects accurately
Band gap must be at useful wavelength (feature size)
Cost and speed of production help
Larger band gap makes system more fault-tolerant (dielectric
constants and geometry)
5µm
This simple cubic structure may be relatively easy
to make, but it has a very small band gap
Looks good, but assembled 1
sphere at a time w/ nanorobotics
Images from S.-Y. Lin et al., JOSA B 18, 32 (2001) and F. Garcia-Santamaria et al., Adv. Mater. 14 (16), 1144 (2002)
Layer by Layer: Electron Beam
Lithography
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E-Beam PMMA pattern, Reactive Ion
Etch Si, fill w/ dielectric, mechanically
smooth, spin on PMMA, repeat
Defects are introduced by over-etching
individual cylinders
Method produces large band gap, can
be adapted for other materials
Side (a) and top (b) view of process
Images from S. G. Johnson et al., Appl. Phys. Lett. 77, 3490 (2000) and modified from S. G. Johnson et al., Nature.
429, 538 (2004)
Layer by Layer: Woodpile
• Process very similar to previous
method
• Grooves etched in substrate, filled
with dielectric, mechanically
smoothed, repeat with groves at 90°
• 3rd layer offset by ½ unit cell
• Many different variations on tech. –
repeat layers, wafer press
• Fair sized band gap, has been
developed for many materials
SEM Micrographs of woodpile structure and
introduction of defect
Images from http://www.sandia.gov/media/photonic.htm and S.
Noda et al., Science 289, 604 (2000)
Serial: 2 Photon Polymerization
Laser Light
• Focused laser light polymerizes bulk
monomer with photoinitiator
• Polymerization occurs only at beam
focus
• Allows for cheap prototyping vs. other
systems, but accuracy not as good
Lens
Woodpile structure created via 2 Photon Polymerization
Monomer, Photoinitiator
Polymer
Image from B. H. Cumpston et al., Nature 398, 51 (1999)
All-at-Once: Inverse Opals
• Self assembling microspheres create FCC
matrix
• Spheres cannot create complete band gap, but
a dielectric filler with hollow spheres can
• 3 photon polymerization used to create defects
after sedimentation of microspheres
• Defects and microspheres removed, but
dielectric filler remains
• Sensitive to defects
Image modified from L. Wonmok, Adv. Materials 14, 271 (2002) and
from Y. A. Vlasov, et al., Nature 15, 289 (2001)
Conclusions
• Many techniques exist for creation of photonic crystals,
and development continues to improve
• The most promising techniques seem to be layer by
layer woodpile, and layer by layer e-beam lithography
• Development of technology for optical computers is a
very active field
SEM Micrographs of
point defects added to
woodpile structures
Image modified from S. Ogawa Science 305, 227 (2004)
References
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http://ab-initio.mit.edu/photons/tutorial/
S. G. Johnson et al., Nature. 429, 538 (2004)
http://www.cns.cornell.edu/NanoPhotonics05Gaeta.html
http://www.icmm.csic.es/cefe/pbgs.htm
S.-Y. Lin et al., JOSA B 18, 32 (2001)
F. Garcia-Santamaria et al., Adv. Mater. 14 (16), 1144 (2002)
S. G. Johnson et al., Appl. Phys. Lett. 77, 3490 (2000)
http://www.sandia.gov/media/photonic.htm
S. Noda et al., Science 289, 604 (2000)
B. H. Cumpston et al., Nature 398, 51 (1999)
L. Wonmok, Adv. Materials 14, 271 (2002)
Y. A. Vlasov, et al., Nature 15, 289 (2001)
S. Ogawa Science 305, 227 (2004)