Overview of course

Capabilities of photonic crystals

Applications

MW 3:10 - 4:25 PM Featheringill 300

Professor Sharon Weiss

What is a photonic crystal?What is a photonic crystal?

Structure for which refractive index is a periodic function in space

1-D photonic crystal

2-D photonic crystal

3-D photonic crystal

yx

z

yxy

What is a photonic crystal?What is a photonic crystal?Propagation of light over a particular

wavelength range is forbidden (called photonic band gap – PBG)

Wavelength (nm)

Ref

lect

ance

(%

)

100

0

60

80

40

20

1000 1400 1800

PBG

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

k X M

a/2

c

PBG

How do you make a photonic crystal?How do you make a photonic crystal?

• Photoresist patterning• Exposure by electron-

beam or stepper• Pattern transfer by

reactive ion etch

• Wet chemistry (opals)• Molecular beam

epitaxy or thin film deposition (multilayer films)

Lithography (top down)

Chemistry (bottom up)

How do you make a photonic crystal?How do you make a photonic crystal?

Lithography (top down)

Chemistry (bottom up)

Blanco et al., Nature 405, 437(2000)Grüning et al., Appl. Phys. Lett. 68, 747(1996)

1.5 m

Emergence of the fieldEmergence of the field

Seminal papers(theory)

First expt. PBGdemonstration

http://phys.lsu.edu/~jdowling/pbgbib.html

Size scalesSize scales

Wavelength range of photonic band gap directly related to feature size of photonic crystal

Refractive index periodicity Photonic band gap wavelength

1 millimeter

1 micron

0.5 micron

0.1 micron

THz

Mid IR

Near IR

Visible

Preview: photonic crystal geometries Preview: photonic crystal geometries and potential applicationsand potential applications

• Bragg mirrors• Microcavities• 1-D PBG waveguides• Omnidirectional mirrors• 2-D PBG waveguides• Add/drop filters• Lasers• Superprism• Fiber• Artificial opals• 3-D PBG woodpile structure

http://www.physics.utoronto.ca/~john/

Bragg mirrorsBragg mirrors

• Earliest example of photonic crystal• Initial applications include mirrors for VCSELs (vertical

cavity surface emitting lasers)• Consists of alternating quarter wavelength optical

thickness high and low refractive index materials

1000 1400 1800

Wavelength (nm)

Ref

lect

ance

(%

)100

0

60

80

40

20

PBG

Effect of Photonic Crystal CompositionEffect of Photonic Crystal Composition

Stopband width increases as index ratio of

nH/nL increases

700 900 1100 1300 1500

Wavelength (nm)

Ref

lect

ance

nH = 2.0

nH = 2.2

nH = 2.4

nH = 2.6

nL = 1.5

700 900 1100 1300 1500

Wavelength (nm)

Ref

lect

ance

nH = 2.0

nH = 2.2

nH = 2.4

nH = 2.6

nL = 1.5nL = 1.5

Omnidirectional MirrorsOmnidirectional Mirrors

A. Bruyant et al., Appl. Phys. Lett. 82, 3227 (2003)

• Completely reflect light for all angles of incidence and all polarizations

Omniguide – Commercial CompanyOmniguide – Commercial Company

• Light guided in air core of hollow tube

• Confinement based on multilayer films that constitute the cladding

Y. Fink et al., J. Lightwave Technology 17, 2039 (1999) http://www.omni-guide.com

MicrocavitiesMicrocavities

• Defect layer breaks periodicity of dielectric function and introduces allowed mode into PBG

Wavelength (nm)

Re

flect

an

ce (

%)

1000 1200 1400 1800 20001600800

100

0

60

80

40

20

1-D Photonic Crystal Waveguides1-D Photonic Crystal Waveguides

• Feature size of 100 nm achieved by x-ray lithography

• Light guided near 1.5m• Missing hole in center enables

resonance wavelength• Changing length of defect tunes

resonance wavelength

J. S. Foresi et al., Nature 390, 143 (1997)

2-D PBG Waveguides2-D PBG Waveguides• Silicon waveguides fabricated by a

combination of lithography and electrochemistry

2 m

F. Muller et al., J. Porous Materials 7, 201 (2000)

M. Loncar et al., Appl. Phys. Lett. 77, 1937 (2000)

Fabrication of 2-D Photonic CrystalFabrication of 2-D Photonic Crystal

Oxidation

Reactive ion etching(CF3 and O2)

KOH etching

Buffered HF

crystalline silicon

oxide

photoresist

Lithography

Spin photoresist

Electrochemicaletching

Add/Drop FiltersAdd/Drop Filters• Theoretically investigated, preliminary experiments• Design of missing holes and enlarged holes allow for

light to selectively exit waveguide

H. Takano et al., Appl. Phys. Lett. 86, 241101 (2005)Y. Akahane et al., Appl. Phys. Lett. 82, 1341 (2003)

Photonic Crystal LasersPhotonic Crystal Lasers

• Incorporation of 2-D photonic crystal with light emitting semiconductor quantum well provides confinement and gain necessary for lasing

O. Painter et al., Science 284, 1819 (1999)

Superprism EffectSuperprism Effect• Light path shows a extremely wide swing with a slight

change of incident light angle• Based on highly anisotropic dispersion by photonic band

(negative refraction)

T. Sato et al., Phys. Rev. B 58, R10096 (1998)

Photonic Crystal FiberPhotonic Crystal Fiber• Light guided in air core instead

of traditional high refractive index core

• Allows for lower losses• 2-D PBG confines light in fiber• Currently 1.2dB/km (traditional

fiber 0.15dB/km)

R. F. Cregan et al., Science 285, 1537 (1999)P. J. Roberts et al., Opt. Express 13, 236 (2004)

Artificial OpalsArtificial Opals

• Chemical synthesis using chemical vapor deposition and wet etch to form air spheres surrounded by silicon shells

• Complete photonic band gapobserved in near-IR

• Easier to achieve smaller dimensions with bottom-up technology

Blanco et al., Nature 405, 437(2000)

1.5 m

Woodpile Structure: 3-D PBGWoodpile Structure: 3-D PBG

• Extremely complicated high tech lithography used to achieve 3-D PBG– Series of deposition, patterning,

etching, and planarization steps

• Light confined in all three dimensions

S. Y. Lin et al., Nature 394, 251 (1998)http://www.sandia.gov/mstc/technologies/photonics/gallery003.html