Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and...

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1 Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center The University of Texas at Austin Nano & Giga Challenges Tempe, AZ; March 15, 2007 * Email: [email protected] or [email protected]

Transcript of Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and...

Page 1: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Photonic Crystals: Physics, Devices, and Applications

Wei Jiang*Omega Optics, Austin, Texas

&

Microelectronics Research CenterThe University of Texas at Austin

Nano & Giga ChallengesTempe, AZ; March 15, 2007

* Email: [email protected] or [email protected]

Page 2: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Outline

• Introduction• Superprism Effect: Physics, Device &

Applications• Silicon Photonic Crystal Waveguide

Modulator

Page 3: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Chase

Telecommunication Network Hierarchy: A Quick Introduction

NYCNYSE

UT IBM

AMD

San Jose

Cisco

SunIntel

WAN: Wide Area Network (WDM)

MAN: Metropolitan Area Network (WDM)

LAN: Local Area Network (Ethernet)

*WDM: Wavelength Division Multiplexing

fiber link Citi

• One promising solution:Optical Interconnects

• Using devices similar to telecomm

Electrical interconnect bottleneck

Austin

Page 4: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Metro WDM Links

Wavelength Division Multiplexing (WDM)

Lasers

VOA’s DeMUXVOA’s

* VOA: Variable Optical Attenuator** Photonic crystal picture source: MIT Joannopoulos group website, & Park et al. Science (2004).

Amplifiers

Switches

Receivers

MUX MUXDeMUX

add

dropinput

Page 5: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Introduction: From 1D to 2D and 3D structures

Γ X M Γ

freq

uenc

(2π

c/a)

= a

/ λ

00.10.20.30.40.50.60.70.80.91

2D Photonic Band Gap

UÕ L Γ X W K

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0

L'

LK'

ΓW

U'XU'' U

W' K

z

3D Photonic Band Gap

Ref: ab-initio.mit.edu/photons/

Γ XM

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• “Optical Insulator” vs. “Optical Conductor”• Initially, proposed for threshold-less laser (compact cavities)• Later, waveguides, modulators, sensors, demultiplexers…

Page 6: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

6Ref: http://ab-initio.mit.edu/photons/

Point Defect : light cavities

Line Defect:waveguides

2D slab PCW: 2D slab + line defect

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Defects

oxideSiair

holes Substrate

Conventional dielectric waveguide

Page 7: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Photonic crystal: from concept to devices

PBG for localization

John

PBG for laserYablonovitch

Woodpile3D PC

Lin, Ho (1998)

1987

Woodpile3D PC cavityNoda (2004)

2D slab defect laserPainter &

Scherer (1999)

Electrically driven 2D slab PC laser

Park & Lee (2004)

SuperprismKosaka (1997)

Refraction theory

Jiang (2005)

SuperprismMonemi & Adibi (2006)

2D PC slabKrauss (1996)

2D PCW in slabMIT (2000)

Slow light in PCW

Notomi (2001)

WDM,Sensor

lasers

Wave-guides

PCW couplingNTT; IBM

(2004)

Channel drop filter Fan&Joannopoulos

(1998)

Filter & CCW Xu&Yariv (2000)

Multi-λJiang (2003)

PCW Switch Vlasov (IBM)

Omega/UT 2005GHz Modulator

Omega/UT (2007)

Filters,OADM

Switch/Modulator

Multi-λNoda (2003)

1997 2007A very brief summary—my sincere apologies for not being able to cover lots of important work in such a short time

Slow-light device Solajcic&Joannopoulos

(2002)

2D slab laserBell Lab/MIT

(1998)

Page 8: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Superprism Effect: Physics, Devices, & Applications

• Introduction: superprism effect• Difficulties in modeling & related physics problem• Our general, rigorous theory• Demultiplexer Design• Polymeric Photonic Crystal Fabrication• Other Applications

Page 9: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Superprism Effect -Anomalous Light Refraction on Photonic Crystal Surface

H. Kosaka et al., Phys. Rev. B 58, 10096 (1998).

H. Kosaka et. al. Appl Phys. Lett., 74, 1370 (1999).

• Strong wavelength-dependent refraction

∆λ/λ=1% ∆θ=50°

∆θ ≅5000(∆λ/λ)∆θ ≅10 (∆λ/λ)

Photonic CrystalConventional

Periodic nanostructures cause the optical properties of photonic crystals to be highly anisotropic

Page 10: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Difficulties in designing superprism devices

• Wavelength demux•Mostly used Finite Difference Time Domain (FDTD) simulations•Demand prohibitive computational resources• In practice

Use large dλ, orSimulate smaller device

Chung & Hong, Appl. Phys. Lett. 81, 1549 (2002).

Baba & Nakamura, J. Quantum Electron. 38, 909 (2002).

0.61

0.48

0.46

0.27

λ’

A sense of “small”

dλ/λ>3% !!

Grid spacing ~0.05λ

Page 11: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Modeling methods Categorized by Efficiency

Transfer MatrixKKR

Single cell methods

Internal Field Expansion, Transfer Matrix

1D supercell

FDTD, spherical wave

Whole space

Need a single-cell modeling method that can handle arbitrary lattice type & arbitrary surface orientation.

Page 12: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Outline of Our Theoretical Technique

• Solved the eigenvalue, eigenmodes given kx ,ω, solve for ky, E(G)

• Boundary matching for N up modesSolve a set of linear equations for

N transmission coefficient ts & N reflection coefficient rl

• Two issues (complicated math)Forward/backward modes partition• Only N up modes are physically meaningful in y>0

Identify degeneracy related to the surface orientation

0)'()()(])()[('

222 =−++++− ∑ GG'GGG

EEGkGk yyxx εωx

y

PC

α

θ

ε I

q

vg

Jiang et al. Phys. Rev. B 71, 245115 (2005).

Page 13: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Difficulties

• Number of equations and number of unknowns both depend on the surface orientation

• Two types of surface orientation

Crystallographic surface with integer Miller indices: (100), (121), (253) …Quasi-periodic surface: (1,π,0), (√2, 0,1)

• Quasi-Periodic Surface can be obtained by flatly terminating an ordinary periodic medium

Penrose tiles: 5-fold symmetry

A1

a

No periodicity

Jiang et al. Phys. Rev. B 71, 245115 (2005).

Page 14: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Mode degeneracy depends on surface orientation

1st BZ

(h1h2)=(01) (h1h2)=(23)

const. kxline

Real Space

ReciprocalSpace

Yu & Fan PRE 2004A slight change of surface orientation may

cause one refracted beam to split into many

dispersion surface (constant-ω contour)(~Fermi surface, constant-E contour)

Jiang et al. Photonics West 2004

Page 15: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Results and Efficiency of Our Method

• FDTD: Calculate field in the whole spaceinefficient• Our Theory: One Cell per Surface• Complete, Rigorous theoretical framework of photonic crystal refraction

Any lattice type and arbitrarysurface orientationBoth planar wave, Gaussian Beam, and arbitrary beam profileQuasi-periodic surface

θscreen

Negativerefraction

Jiang et al. Phys. Rev. B 71, 245115 (2005).

Page 16: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Demultiplexer Design: What bevel(s) is best

input

λnλn-1λ1 λ2

wide PC region—bulky

λnλn-1

λ1

photonic crystal

input

λ2

compact

Beam splitting for 30o bevel,High loss

Page 17: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Applications

• Negative index materials (NIM)• Laser Beam Steering with Electrical

Control• Sensing (sensitive to index change)• Grating Diffraction (“Virtual Photonic

Crystal”)

∆θ ≅10 ∆λ/λ∆θ ≅5000 ∆λ/λ

∆θ ≅10 ∆n∆θ ≅5000 ∆n

Conventional medium

photonic crystal Ultra-high dispersion translates into 500 times higher sensitivity to the change of refractive index

Page 18: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Fabrication- Holography & Nanoimprint

Prism Holography- First holographic PC with a stopband covering S+C bands for fiber-optic communication wavelengths- Simpler and cheaper than the grating approach

J. Chen, W. Jiang et al. Appl. Phys. Lett. vol. 90, 093102 (2007).

AFM 3D topology

Nanoimprint• low cost, high thru-put

L. Wang, W. Jiang et al. JAP (accepted)

Page 19: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Compact, Low-voltage Si Photonic Crystal Waveguide Modulators

- Outline

• Basic ideas & Physics• Design considerations• High J, V, and P issues for GHz

modulation in Silicon• Measurement & Results

Page 20: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Intel’s Silicon Modulator

Liu et al, Nature 2004

• Overcame the GHz barrier for silicon modulator• Large size undesired

Page 21: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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►Modulation efficiency enhancementthrough highly-dispersive PCWs

Advantage: Significant reduction in interaction length

smaller device & low power consumption

Working Mechanism:

LV

LddL

g00

1~ ωωωββφ ∆∆=∆=∆

0→=pc

g ddVβω

L for same ∆Ф

Photonic Crystal Waveguide Modulator:Basic Principles

►Index tuning through plasma dispersion effect

Soljacic et al JOSA B 2002.

nnnN effe ∆=∆⎯⎯ →⎯∆⎯⎯ →⎯∆ 100 Plasma dispersion

Slow lightPCW

Light travels slower in a PCW and has more time interacting with electrons. This results in enhanced light-matter interaction.Refractive index of silicon

∆β

∆β=∆ω0/vg

Page 22: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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siliconair holes

Photonic Crystal Waveguides - Basics

• Photonic crystalwaveguide: Physics

mode dispersion relation & field patternSlow Light

oxide

Horizontal: photonic band-gap guiding(all-angle in-plane Bragg Reflection)

Vertical: index guiding

Page 23: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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A host of structures

(d)

p-doped poly-Sin-Si

electrode

(e)

(a)oxide

air holes

electrode

n++ p++

(c)substrate

n-Si thin oxide

Need thick poly-Si to reduce metal absorption, this causes:• Multi-mode PCW• High current density• Not planarized

electrodes

Electrical driver

From Day ONE:• Need to connect inner electrode to the outside• Integration with on-chipelectrical driver• Not trivial

air holes

electrode

n++ p++(b)substrate

“intrinsic” Si

oxide

Shih et al APL, 2004.

Page 24: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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-- -

+

Photonic crystal laser

Park et al. Science 2004

Photonic crystal as an Optical Insulator AND an Electrical Conductor

++

+-

--

Resistance R~1.4 R0

+-• Resistance R~4 R0• Insufficient vertical carrier diffusion causing poor overlap of ∆Ne(x) & optical field I(x)

Conventional modulatorPhotonic Crystal modulator

Page 25: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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P-I-N Diode Modulator:Modulation mechanism

• High Voltage problem: 6.5V (intel), ~20V (Cornell)

• Scaling Law Regardless of detailed transport mechanism(s)

∆t=qwcore(∆Nh)c/J or J=2qwcore(∆Nh)cf• Example: Let J=qnµE gives

Drift time limit: t=wcore/µE• The parameters present are somehow fixed:

wcore~1µm (~λ) (∆Nh)c~3x1017 cm-3 for Silicon (from Soref & Bennett JQE 1987)

• Minimum AC current density J~104A/cm2 for 1GHzhigh injection regime—important implications: need low R,

hehe

hehe

NNNNnnn

∆×+∆×=∆+∆=∆

∆×+∆×−=∆+∆=∆−−

−−

1818

8.01822

100.6105.8])(105.8108.8[

ααα

Page 26: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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P-I-N Diode Modulator:Modulation mechanism (cont’d)

M. Lipson, Nanotechnology 2004

High injection regime &Non-ideal diode behavior:• Ideal diode

∆Nh=(ni2/Ndi) exp(qVj/kBT)

I~exp(qVj/kBT)

• Non-ideal∆Nh=ni exp(qVj/2kBT)I~exp(qVj/2kBT)

At Vj=V0 (contact potential)• Ideal diode

∆Nh=Na~5×1019 cm-3

• Non-ideal diode∆Nh=(NaNdi)1/2~2.3×1017 cm-3

Magic number for Si modulator

Page 27: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Fabrication & Spectrum

•Slow group velocity: c/40• Expected modulator interaction length reduction: 20X ~ 40X• High Group velocity Dispersion (GVD)

Page 28: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Device Structure, Simulation, and Testing Result

N- (I)

1x1015/cm3

W I = 4µm2µm

P+

5x1019/cm3

N+

5x1019/cm3

Lateral electrodes

Buried oxide

Si substrate

N- (I)

1x1015/cm3

W I = 4µm2µm

P+

5x1019/cm3

N+

5x1019/cm3

Lateral electrodes

Buried oxide

Si substrate

L. Gu, W. Jiang et al. Appl. Phys. Lett. 90, 071105 (2007).

80 µmπD~36µm2.5mmInteraction Length

42%90%N.A.Modulation depth (1GHz)

2V20V6.5VPeak Voltage

Omega /UT CornellIntel

Page 29: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Summary

• Photonic crystals bring compact photonic devicesA compact wavelength demultiplexer

• In some devices (e.g. modulators), reduced device size also helps reduce current, voltage and power consumption

demonstrated a compact, low-voltage, high-speed Si modulator using photonic crystal waveguides

• Solid state physics theory for transmission through naturally cut quasi-period surface, and for more general interface transmission problems of any lattice and any surface orientation

• Scaling law of high speed silicon modulator & minimum current density for gigahertz modulation

Page 30: Photonic Crystals: Physics, Devices, and Applications · Photonic Crystals: Physics, Devices, and Applications Wei Jiang* Omega Optics, Austin, Texas & Microelectronics Research Center

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Acknowledgement

• UT Faculty membersProf. Ray T. ChenProf. Sanjay BanerjeeProf. Michael BeckerProf. Herbert L. BerkProf. Joe C. CampbellProf. Ananth DodabalapurProf. Ben Streetman, Dean

• Chen group membersMaggie ChenXiaonan ChenJiaqi ChenLanlan GuBrie HowleyYongqiang Jiang Boem-suk Lee Xuejun LuLi WangXiaolong Wang

• Outside ResearchersProf. Paul BindingProf. Shanhui FanProf. Nick X. Fang Prof. Joe HausProf. Sajeev JohnProf. Lifeng LiDr. Yao LiDr. Richard Soref

• Other MER StudentsWeiping BaiHao ChenXiangyi GuoNing LiDingyuan Lu

• SponsorsDr. Robert NelsonDr. Gernot Pomrenke

Additional support to Chen Group• DARPA• State of Texas, Sematech• SPRING