Breaking the Bandwidth Bottleneck in Telecommunications & Information Processing:

New Electro-Optic Materials

Larry DaltonDepartments of Chemistry, Materials Science & Engineering,

and Electrical EngineeringUniversity of Washington & University of Southern California

AcknowledgementsFinancial support provided by the National Science Foundation and the Air

Force Office of Scientific Research

10th Foresight Conference on NanotechnologyOctober 11-13, 2002

•Semiconductor Research Corporation Workshop on Optical Interconnectshttp://www.src.org/member/sa/nis/E002117_Opto_wksp.asp

•British House of Lords Select Committee on Science & Technology Study of Innovations in Computer Processors

•Forthcoming article in IEEE Computing

•High frequency, ultra high stability clocks

•On-chip signal distribution

•Chip-to-chip interconnection

•Module-to-module interconnection

Critical to Next Generation Computing

From: "PARK,CHRIS (A-England,ex1)" <chris_park@agilent.com>To: "'Larry Dalton'" <dalton@chem.washington.edu>Cc: "MEADOWCROFT,SIMON (A-England,ex1)" <simon_meadowcroft@agilent.com>Subject: Collaboration with Agilent TechnologiesDate: Tue, 2 Jan 2001 15:54:07 +0100  

Dear Prof Dalton, 

Agilent Technologies would like to meet with you to find out more about your work on high speed polymer modulators. Our interest is based on a need to manufacture low cost 100 Gigabit Ethernet optical components in approximately 3 years time using technologies which are compatible with high volume and low manufacturing cost. The work you have published on high speed modulators is currently one of the best alternatives for a low component count, low modulation voltage 100GbE transmitter. Agilent Technologies would therefore be interested in discussing your work and the options for collaboration. These options can include research sponsorship and/or business development including support for new start-up activity. Simon and I will be attending OFC in Anaheim and would like to meet with you that week, or if you are not attending OFC we could visit Washington early the following week (w/c 26th March).Please let us know whether you are available at this time. 

Best regards 

Dr Chris ParkResearch ManagerAgilent TechnologiesWhitehouse RdIpswichUKTel 44 1473 465628e-mail chris_park@agilent.com

Critical to Telecommunications Industry

Electro-Optic Devices: The on-ramps & interchanges of the information superhighway

(The Metro Loop and Fiber to the Home)

Critical to Defense IndustryCritical to Defense Industry

U WashingtonU WashingtonCaltechCaltech

Electro-Optics: The Phenomena

An electro-optic material (device) permits electrical and optical signals to “talk” to each other through an “easily perturbed” electron distribution in the material. A low frequency (DC to 200 GHz) electric field (e.g., a television [analog] or computer [digital] signal) is used to perturb the electron distribution (e.g., -electrons of an organic chromophore) and that perturbation alters the speed of light passing through the material as the electric field component of light interacts with the perturbed charge distribution.

Because the speed of light is altered by the application of a control voltage, electro-optic materials can be described as materials with a voltage-controlled index of refraction.

Index of refraction = speed of light in vacuum/speed of light in material

Electro-Optic Devices: The on-ramps & interchanges of the information superhighway

The electro-optic effect can be used to transduce electrical information (signals) onto the internet (in to optical signals). By slowing light down in one arm of the Mach Zehnder device shown below, the interference of light beams at the output can be controlled. Electrical information appears as an amplitude modulation on the optical transmission. This works equally well for analog or digital data.

DC bias electrodeground electrode

Substrate

RF electrode

Light InModulatedLight Out

What are the critical requirements for EO materials and devices?

Low halfwave voltage is a critical requirement in externally modulated photonic systems:

Analog systems: For RF transparency:

Link gain 1/V2

For high dynamic range:NF V

2

(low level signal detection limited by noise floor)

Digital systems:High speed digital circuits have low output voltage

Digital amplifiers very costly

Bandwidth is the other critical requirement!

Why Organic Electro-Optic Materials (Devices)?

.

•Intrinsic material bandwidths of several hundred gigahertz. The response time (phase relaxation time) of -electrons in organic materials to electric field perturbation is on the order of femtoseconds. Operational bandwidths of 150 GHz have been demonstrated for modulators & switches•Organic electro-optic coefficients are currently 2-4 times higher than lithium niobate and getting larger. Theoretically-inspired rational design of materials will keep electro-optic activity improving for several years. Device operational voltages of less than 1 volt are routine.•Organic EO materials are highly processable into 3-D circuits and can be easily integrated with semiconductor VLSI electronics and silica fiber optics. Low loss coupling structures can be straightforwardly fabricated.

Comparison of Material Performance

Property Polymer (at 1.3m) Polymer (at 1.55m) Lithium Niobate

EO Coefficient (r) 130 pm/V 60 pm/V 32 pm/V

Optical Loss 1 (0.7) dB/cm 1 (0.2) dB/cm 0.2 dB/cm

Bandwidth•Length >350 GHz•cm >350 GHz•cm 10 GHz•cmProduct

Dielectric Constant () 2.5-4.0 2.5-4.0 28

Refractive Index (n) 1.5-1.7 1.5-1.7 2.2

Figure of Merit (n3r/) ~100 ~100 6

Thermal Stability 85 ºC 85 ºC (90 ºC)

State-of-the-art High Speed Infrared ModulatorsCommercial Lithium Niobate Devices—The CompetitionV: 6 V @1550 nm, 30 GHz Bandwidth, $6000/per unitCommercially Available Polymer Devices V: 1.2 V @ 1300 nm, 1.8 V @1550 nm20 GHz and 30 GHz Bandwidth (3dBe)Published Prototype Device ResultsV: 0.77 V @ 1300 nm100 GHz operationRecent Dendrimer Device ResultsV: 0.5 V @ 1550 nmRecent MR Device ResultsV: < 1 V @ 1550 nm

Comparison of Lithium Niobate and Polymer Electro-Optic Modulators

10 Modulator Chips on 3 Inch Wafer

2 Push-Pull MZ Modulators on One Chip

Why Nanostructured Electro-Optic Materials?

•Noncentrosymmetric ordering of chromophores (all pointing in the same direction) in the material lattice is required for electro-optic activity. Chromophore dipole-dipole interactions oppose this ordering. Forces must be used to achieve the desired order and chromophores must be positioned precisely in space to minimize the undesired effects of dipole-dipole interactions.

•A uniform chromophore distribution (and high concentration) is necessary not only to maximize electro-optic activity but also to avoid optical loss from scattering off of material density (index of refraction) variations.

•Several routes to nanostructured electro-optic materials are being pursued including (1) the electric field poling of dendritic materials and (2) sequential (layer-by-layer) synthesis from an appropriate substrate (which also serves as a cladding material).

Theoretically inspired rational improvement of organic electro-optic materials

•Theory (quantum and statistical mechanics have guided the systematic improvement of the hyperpolarizability () of organic chromophores and the electro-optic activity of macroscopic materials, e.g.,

Systematic Improvement in Molecular Electro-Optic Activity: Variation of

N NO2R

R

N NR

R

N NO2

N

R

R

SN

OO

Ph

ISX

N

R

R

S CN

NC

CF2(CF2)5CF3

N

R

R

NO

O

Ph

FCN

APTEI

N

R

R

S

NC

CN

NC

CN

TCI

N

R

R

S CN

NC

CN

N

R

R

S CN

NC

CN

TCV

N

R

R

S SO2

NC

CNTCVIP

SDS

N

R

R

SO

NCCN

NC

N

R

R

O

NCCNNC

R'

NA

DR, 30 wt%, r33 = 13 pm/V

FTC, 20 wt%, r33 = 55 pm/V

CLD

(x10-48 esu)

80

580

2,000

3,300

4,000

6,100

(x10-48 esu)

9,800

13,000

15,000

18,000

30,000

New Advances in Chromophore Development

.

New Paradigm:Gradient-Bridge, Mixed-Ligand-AcceptorChromophores

Quantum mechanical calculations permit the optimization of the -electron structure that defines molecular hyperpolarizability.

New Synthesis Techniques: Microwave synthesis techniques permit dramatic enhancement in reaction yields and synthesis of new materials.

N

SS

N

N

N

HO

OH

O

D D

C

B

A

A, B, C = NO2, CN, SO2CF3, etc.

D = CF3, etc.

Why Microwave Synthesis?

.

•Microwave synthesis has permitted dramatic enhancement in reaction yields, reducing time devoted to purification. It has also permitted many materials to be synthesized for the first time and has permitted greater flexibility in reaction conditions.

•Microwave synthesis techniques obviously permit more uniform heating of reaction mixtures. The absence of thermal gradients and “hot spots” helps minimize decomposition and side reactions. Microwave synthesis permits the use of a wider range of solvents.

•We have found this approach to be particularly effective for condensation, addition, and de-protection reactions.

CF3

Oi,

ii, dilute HCl

OEt

Li

O

CF3

OH

70%

O

CF3

OH

2CN

CN

O

CN

F3C

CN

CN

Condition Base Reaction time Yield (%)

Reflux

Microwave

LiOEt

NaOEt

48 h

20 min

30

55

CF3-TCF

-Hydroxyketone

Table. Comparison of conventional and microwave methodologies

Condensation

Comparison of Microwave & RefluxSynthesis of CF3-TCF acceptor

Microwave Synthesis: Examples of Syntheses of New Acceptors

.

O

OH+

CN

CN

Microwave 20 W

EtONa/EtOH O

CN

NH

O

CN

NH+

CN

NO2

Microwave 20 W

EtONa/EtOHO

CN

CN

NO2

+CN

COOEt

Microwave 20 W

EtONa/EtOHO

CN

CN

COOEt

O

CN

NH+

Microwave 20 W

EtONa/EtOHO

CN

N

NO

O

S

Et

EtN

N

O

O

Et

Et

S

12

1 3

14

O

OH+

CN Microwave 20 W

EtONa/EtOH O NHN

N

+CN

CN

Microwave 20 W

EtONa/EtOH O

N

CN

CN

5 6

O

CF3

OH+

CN

CN

Microwave 20 W

EtONa/EtOH O

CN

NHF3C

+CN

CN

Microwave 20 W

EtONa/EtOHO

CN

F3C

CN

CN

78

Coupling Reactions

.

NBu

Bu

S O

O

CN

CN

CNF3C

, 20W, 8 min.N

Bu

Bu

S O

NCCN

CN

CF3

OTBDMS

OTBDMSEtOH

NBu

Bu

S O

O

CN

CN

CNF3C

EtOH, reflux

NBu

Bu

S O

NCCN

CN

CF31.5 hr.

NBu

Bu

O

NC

CF3

NC

CN

NBu

Bu

O+

O

CN

CN

CNF3C

cat. Py. Piper.

THF, CHCl3, reflux

NBu

Bu

O

NC

CF3

NC

CN

NBu

BuO

CN

CN

CNF3C

cat. Py. Piper.

THF, CHCl3, reflux

O

+

LMAJ 22

LMAJ 24

1

2

Centric Ordering

E

Chromophore-polingField Interaction

Thermal Randomization Chromophore-ChromophoreElectrostatic Interaction

Acentric Ordering Isotropic

<cos3>= F/5kT = f(0)Ep/5kT

<cos3> =(F/5kT)[1-L2(W/kT)]

34

cosn

NFreff

Translating Microscopic to Macroscopic Electro-Optic Activity

Comparison of Potential Functions from Analytic Theory & Monte Carlo Calculations

Solid Line—Analytic Theory

Centric Order

Acentric Order

2 22 2

3

Nw s s

r kT kT

.

0.3 cosexp wP A

Points—Monte Carlo Calculation

Comparison of Theory & Experiment

.

Experiment—SolidDiamonds

2max 2 2

0.48 0.28 4.8 kT kT

N f

Prediction of the Dependence on Electric Poling Field

.

Theory-Guided Nano-Engineering: Generalization of the Use of Dendronized Chromophores

.

New Paradigm: The Concept of Dendronized Chromophores Can Be Generalized.

: Dendritic moiety

: Polymer backboneCore moiety

: NLO chromophore moiety

: Crosslinkable moiety:

x yx y

Side-Chain dendronized NLO polymer

Dendritic NLO chromophore

NLO dendrimer

Statistical Mechanics Guides the Optimization of Macroscopic Electro-Optic Activity

.

New Paradigm: Dendrimer synthesis of theoretically-predicted optimum chromophore shapes—nano-architectural engineering.

Core moiety

: NLO chromophore moiety

: Dendritic moiety

: Crosslinkable moiety

:

With electric field poling and crosslinking, multi-chromophore dendrimers assume partially closed umbrella-like shapes. Also, these dendrimers don’t interpenetrate. These two observations are supported by theoretical calculations and experimental observations.

Control of Intermolecular Electrostatic Interactions Using Multi-Chromophore Dendrimers

O

O

OO

O

ON

S

CNNC

NC

NC

O

O

O O

FF

OF

O

O

FF

OF

O

N

S

NCCN

NC CNO

O

O

OF

F

O

FO

OF

F

O

FO

NS

NCCN

CN

CN

O

O

OO

F F

O F

O

O

F F

O F

O

O

O

O

Jen, Dalton et al., J. Am. Chem Soc, 123, 986 (2001)

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100

r33

(t)/

r33

(0)

Time (hr)

Twice the EO activity of samechromophore in polymer matrix—record value at 1.55 microns.Factor of 2 in thermal stability.

Thermal stability of EO activity at 85 C

Dendronized Chromophores: An example

.

Dendronized chromophore yields 3 times the electro-optic activity and reduced optical loss (next figure).

N

S

NC CN

NC

NCO

O O

O O

O

O

O

O

O

O

O

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

FF

F

F

F

F

F

F

F

F

F

F

F

F

N

S

NC CN

NC

NC

FLDRTCBD

Photothermal deflection spectra (PDS) of FLDR/APC

0.1

1

10

100

1000

10000

100000

1000000

0 500 1000 1500 2000

Wavelength (nm)

0.85 dB/cmat 1.55 mm

0.68 dB/cm at 1.3 mm

Perfluorodendron-substituted Chromophore Contributes Little to Optical Loss in Guest-Host APC Polymer

Perfluroinated Chemophore-Containing Dendrimers: Low Total Optical (Absorption and

Scattering) Loss

0

0.05

0.1

0.15

0.2

0.25

0.3

1480 1500 1520 1540 1560 1580 1600

Wavelength (nm)

Op

tica

l Lo

ss (

dB

/cm

)

HO OH HO OH

OH

1. spin cast with diisocyanate crosslinker

2. electric field poling 3. thermal crosslinking

x y z

free-radical copolymerization with methyl methacrylate and

hydroxyethylmethacrylate

3-D crosslinked network

THERMAL STABILITY—The Need to Lock-In Poling Induced Acentric Order: Intermolecular Crosslinking

Optimizing Photostability

.

•Photochemical stability can be improved by chromophore design. Lumera has demonstrated this.

•Photochemical stability can be improved by the use of scavengers (see below), packaging, and lattice hardening.

Photo Stability of Different FTC Samples

0

20

40

60

80

100

120

0 50 100 150 200

UV Exposure Time (minute)

Inte

ns

ity

Ra

tio

(%

)

FTC in Air

FTC Sealed

FTC w/ Quencher in Air

FTC w/ QuencherSealed

0 5 10 15 20 25 300

1

2

3

4

5V

Time [days]

Photostability--Packaged in Argon 50 mW (1550nm) at the output fiber

Exposed over 30 days, V change negligible

Reduce free O2 . Clearly some oxygen is

present in this test.

Improvement in Photostability by Simple Packaging

Processability: An Advantage of Organic Electro-Optic Materials

•The tailorability of organic materials and particularly of dendrimers permits integration of organic EO materials with virtually any material (silicon, silicon dioxide, Mylar, III-V semiconductors, metals, etc.)•Hardened organic EO materials are amenable to reactive ion etching (RIE) and to various photolithographic processes. Processing is very compatible with semiconductor processing techniques.•Organic materials are quite robust (high dielectric breakdown, good thermal stability at most processing temperatures, high radiation (gamma, high energy particle) damage thresholds, etc.•Likely amenable to high volume manufacturing using processing techniques such as spin casting and dry etching.•Straightforward fabrication of an array of prototype devices.

Variable PhotoresistExposure

RIE SlopeTransfer

WaveguideCompletion

UV

OxygenIons

Cladding

Substrate

Photoresist

Core

Spin-CastingPreserves

Surface Contour

Cladding

Reactive Ion Etching of 3-D Optical Circuits

• Computer Generated Layout

• Variable Transmission Exposure– Height Exposure Level

– Angles: 0.1-3°

– Heights: 1-15m

– Lengths: 100-2,000m

• Entire Device Contoured– Complex Patterns Possible

– 10m Resolution

• Precision of Mask Aligner

• Repeatable Quality

UV

Mask

Photoresist

6

4

2

00 50 100 150 200

Hei

ght (

m)

Length (m)

Fabrication of Vertical Slope Using Gray Scale Mask Lithography

Fabrication: Shadow Etch

• Shadow Masking of Ions– Angle RF Power, Gas Pressure,

Time, Mask Dimensions

– Angles: 0.1-3°

– Heights: 1-9m

– Lengths: 200-2,000m

• Fast Prototyping– Various Angles From Single Mask

– No Extensive Fabrication Steps

• Repeatable Quality

4

2

0

0 400 800 1200 1600

Hei

ght (m

)

Length (m)

Mask

Polymer

Offset

6

Oxygen Ions

n(active) > n(passive)

Length

Tapered Transitions: Minimization of Coupling Loss

small length material loss large length radiation loss

Fabrication

Lower Electrode Vertical Slope

Waveguide RidgeUpper Coatings

3-D Modulators

=1.3m

Vertical Integration of EO Circuitry with VLSI Electronics

Electronics

Polymer EOModulator

Silicon

8

4

0

Vol

ts

time

8

4

0

Vol

ts

Vout #1

Modulation Intensity (#1)

Vout #7

Modulation Intensity (#7)

Vertical Integration of EO Circuitry with VLSI Electronics

Waveguiding on Planarized “Optical” Substrate

Optical qualitysurface

PC3 6000Planarizing Polymer

VLSI Circuits

Before Planarization After Planarization

In CoupledLight

Out CoupledLight

• Prism coupled.•= 1.06µm.

6 µm

Loss for waveguides on planarized substrates comparable to virgin SiO 2 substrates

Vertical Integration of EO Circuitry with VLSI Electronics

= Metal

= Glass Substrate

= Photoresist

= Spin On Glass

= Planarizer

1. 2. 3.

4.

CF4 Plasma

Meter

O2 Plasma + Metal

Re-configurable optical waveguide cross connect. The streets and avenues are fabricated on different levels with the ring resonator switchesin between at each junction.

Laser1,2, 3

Modulates1 Modulates2Modulates3WDM modulation module.

Each wavelength modulated byseparate resonate modulator.

1,2, 3

1 32

Integrated wavelength add-drop filter

IMPROVED PROCESSABILITY: POLYMER MICRO-PHOTONIC RING RESONATORS

POLYMER MICRO-PHOTONIC RING RESONATOR USING ELECTRO-OPTIC POLYMERS

5m

4.5m

3m

Si

UV15

CLD1 CLD1

SU-8

UFC 170

Au

Au Au

CROSSECTIONGND

Au upper modulation electrode

Complementary modulated output

Input Modulated output

Why Polymers?-Wide range of indices of refraction-Easy fabrication on multiple levels and integration with other devices-Voltage tunable filter or switch/ modulator using electro-optic polymers-Compact structure; size limited by index contrast-Temperature tuning, 0.1nm/C (use as an advantage or eliminate by athermal design in which thermal expansion of polymer substrate balances dn/dT of waveguide)

INTEGRATED WDM TRANSMITTER-RECIEVER

1, 2, 3

1 32

Laser1, 2, 3

Modulates 1 Modulates 2Modulates 3

Transmitter Receiver

1, 2, 3

1 32

1, 2, 3

1 32

Laser1, 2, 3

Modulates 1 Modulates 2Modulates 3

Laser1, 2, 3

Modulates 1 Modulates 2Modulates 3

Transmitter Receiver

dn

rnKv

V

BW

e

o

FWHM 233

3

Eye diagram1 Gb/s, Vpeak = 1 VDevice has ~2GHz BW

Au Electrode

SU-8

Gold ground

GND

= 2 GHz/V

• Dalton, Steier, et al., “Polymeric waveguide prism based electro-optic beam deflector,” Opt. Eng., 40, 1217-22 (2001)

• Dalton, Steier, et al., “Beam deflection with electro-optic polymer waveguide prism array,” Proc. SPIE, 3950, 108-116 (2000)

• Dalton, Steier, et al., “Polymeric waveguide beam deflector for electro-optic switching,” Proc. SPIE, 4279, 37-44 (2001)waveguide layer formed by

photopolymer

silicon substrate

Recording beam #1 Recording beam # -1

hologram patternbeing formed

cladding polymer

X

Y

Z

hexagonal wavevector lattice of thecombination of recording beams

# 1# -1

# 1'

# -1' # 1''

# -1''

Large Angle, Fast Response Spatial Light Modulator (SLM)

Schematic Diagram Experimental Results

Photonic Band Gap Fabrication

Literature Citations

Phased Array Radar with Photonic Phase Shifter (1 of 3 approaches)

Dalton, Steier, Fetterman, et al., IEEE W & Guided Wave Lett., 9, 357 (1999)

High Bandwidth, Ultrastable Oscillators (Signal Generators)

Diode PumpedNd:YAG Laser

(1.3m)

OpticalIsolator

/2Plate

PolarizingBeamsplitting

Cube

CollimatingLens

2x2Coupler

OpticalSpectrumAnalyzer

PD

Low NoiseAmplifier

YIG TunedBandpass Filter

20 dBCoupler

SpectrumAnalyzer

• Dalton, Steier, Fetterman, et al., “Photonic control of terahertz systems,” Terahertz Electronic Proceedings, 102-5 (1998)

• Dalton, Steier, Fetterman, et al., “Electro-optic applications,” in Encyclopedia of Polymer Science and Technology (J. Kroschwitz, ed) Wiley & Sons, NY, 2001

100 Gbit/sec Analog-to-Digital Converter(1 of 2 approaches)

• Dalton, Steier, Fetterman, et al. “Time stretching of 102 GHz millimeter waves using a novel 1.55 mm polymer electrooptic modulator,” IEEE Photonics Technology Letters, 12, 537 (2000))

• Dalton, Steier, Fetterman, et al. “Photonic time-stretching of 102 GHz millimeter waves using 1.55 mm polymer electro-optic modulator,” Proc SPIE, 4114, 44 (2000).

High Bandwidth Optical Modulatorsand Switches (The Electrical Problem)

Two bands approach:• DC-65 GHz direct modulation, use one modulator section;• 65-130 GHz using upconversion scheme, RF applied to one modulator section, and LO applied to the other section.

Steier, Bechtel, Dalton et al., Proc. SPIE, 4114, 58-64 (2000).

4

1, 2, 3

filter

Electro-optic SSB modulator

AmplifierEO phase shifter

Low loss passive guide

Electro-optic guide

Amplifying guide

HYBRID INTEGRATION POLYMER PHOTONIC MODULE

OBJECTIVE – Develop photonic modules which integrate multiple waveguidedevices and Si electronics into single package.APPROACH – Use 3D integration concepts to integrate different photonic polymersinto single photonic circuit. Use adiabatic coupling in tapered guides for low loss coupling between various materials. Fabricate polymer devices on top of processedSi integrated electronics. Reduce fiber coupling loss by symmetric design of passive waveguides

Si Electronics