1. 10th Foresight Conference on Nanotechnology
October 11-13, 2002
Breaking the Bandwidth Bottleneck in Telecommunications & Information Processing: New Electro-Optic Materials
Larry Dalton
Departments of Chemistry, Materials Science & Engineering, and Electrical Engineering
University of Washington & University of Southern California
Acknowledgements
Financial support provided by the National Science Foundation and the Air Force Office of Scientific Research

2. Critical to Next Generation Computing
•Semiconductor Research Corporation Workshop on Optical Interconnects
•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

3. Critical to Telecommunications Industry
From: "PARK,CHRIS (A-England,ex1)"
To: "'Larry Dalton'"
Cc: "MEADOWCROFT,SIMON (A-England,ex1)"
Subject: Collaboration with Agilent Technologies
Date: Tue, 2 Jan :54:
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 Park
Research ManagerAgilent Technologies
Whitehouse Rd, Ipswich, UK
Tel

4. Electro-Optic Devices: The on-ramps & interchanges of the information superhighway (The Metro Loop and Fiber to the Home)

5. Critical to Defense Industry
Caltech
U Washington

6. 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., p-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

7. 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.
Modulated
Light Out
Light In

8. 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/Vp2
For high dynamic range:
NF  Vp2
(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!

9. Why Organic Electro-Optic Materials (Devices)?
•Intrinsic material bandwidths of several hundred gigahertz. The response time (phase relaxation time) of p-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. .

10. Comparison of Material Performance

11. Comparison of Lithium Niobate and Polymer Electro-Optic Modulators
State-of-the-art High Speed Infrared Modulators
Commercial Lithium Niobate Devices—The Competition
Vp: 6 V @1550 nm, 30 GHz Bandwidth, $6000/per unit
Commercially Available Polymer Devices
Vp: nm, 1.8 nm
20 GHz and 30 GHz Bandwidth (3dBe)
Published Prototype Device Results
Vp: nm
100 GHz operation
Recent Dendrimer Device Results
Vp: nm
Recent MR Device Results
Vp: < nm
10 Modulator Chips on 3 Inch Wafer
2 Push-Pull MZ Modulators on One Chip

12. 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).

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

14. Systematic Improvement in Molecular Electro-Optic Activity: Variation of mb

15. New Advances in Chromophore Development
Quantum mechanical calculations permit the optimization of the p-
electron structure that defines molecular hyperpolarizability.
New Synthesis Techniques: Microwave synthesis techniques permit dramatic enhancement in reaction yields and synthesis of new materials. .
New Paradigm:
Gradient-
Bridge, Mixed-
Ligand-Acceptor
Chromophores

16. 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. .

17. Comparison of Microwave & Reflux Synthesis of CF3-TCF acceptor

18. Microwave Synthesis: Examples of Syntheses of New Acceptors.

19. Coupling Reactions .
Knoevenagel condensations of electron donor-conjugation bridge moieties with acceptors is shown. Synthetic details have been omitted but there are a great many subtle details.

20. Translating Microscopic to Macroscopic Electro-Optic Activity

21. Comparison of Potential Functions from Analytic Theory & Monte Carlo Calculations
Points—Monte Carlo Calculation
Solid Line—Analytic Theory
Centric Order .
Acentric Order

22. Comparison of Theory & Experiment
Experiment—Solid
Diamonds .

23. Prediction of the Dependence on Electric Poling Field.

24. Theory-Guided Nano-Engineering: Generalization of the Use of Dendronized Chromophores
New Paradigm: The Concept of Dendronized Chromophores Can Be Generalized. .

25. Statistical Mechanics Guides the Optimization of Macroscopic Electro-Optic Activity
New Paradigm: Dendrimer synthesis of theoretically-predicted optimum chromophore shapes—nano-architectural engineering. .
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.

26. Control of Intermolecular Electrostatic Interactions Using Multi-Chromophore Dendrimers
Twice the EO activity of same
chromophore in polymer matrix—record value at 1.55 microns.
Factor of 2 in thermal stability.
Thermal stability of EO activity at 85 C
Jen, Dalton et al., J. Am. Chem Soc, 123, 986 (2001)

27. Dendronized Chromophores: An example
Dendronized chromophore yields 3 times the electro-optic activity and reduced optical loss (next figure). .

28. Perfluorodendron-substituted Chromophore Contributes
Little to Optical Loss in Guest-Host APC Polymer
0.85 dB/cm
at 1.55 mm
0.68 dB/cm
at 1.3 mm
APC actually dominates the optical loss

29. Perfluroinated Chemophore-Containing Dendrimers: Low Total Optical (Absorption and Scattering) Loss

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

31. 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. .

32. Improvement in Photostability by Simple Packaging
Photostability--Packaged in Argon
50 mW (1550nm) at the output fiber
Exposed over 30 days, Vp change negligible
Reduce free O2 . Clearly some oxygen is present in this test.

33. 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.

34. Reactive Ion Etching of 3-D Optical Circuits

35. Fabrication of Vertical Slope Using Gray Scale Mask Lithography

36. Fabrication: Shadow Etch
Oxygen Ions
Shadow Masking of Ions
Angle µ RF Power, Gas Pressure, Time, Mask Dimensions
Angles: °
Heights: 1-9mm
Lengths: ,000mm
Fast Prototyping
Various Angles From Single Mask
No Extensive Fabrication Steps
Repeatable Quality
Mask
Offset
Polymer 6 4
this technique consists of merely placing a shadow mask above the film before placing the sample in the etching chamber. The variable etch rate on the surface of the film is due to both the directionality and diffusion of the etching ions. The slopes produced depend on the etching parameters, of power and pressure, and on the dimensions f the mask..specifically its length ad vertical offset from the film surface. For a mask we used a standard microscope slide vertically offset from the film surface by 1-2mm.
using this method, we can produce slope ranging from 0.1 to 3° in thicknesses up to 9um. This graph shows a typical slope that we can produce. It has a height of about 5.5um and a slow taper length of about 1000um.
this method is useful for prototyping new device designs because a single mask can be used to fabricate a wide range of angles. Also, no extensive fabrication steps are required. Specifically no photolithography is needed.
to evaluate the optical quality of these slopes and their performance as adiabatic tapers, we next fabricated passive waveguide interconnects m
Height ( m) 2
400
800
1200
1600
Length (mm)

37. Tapered Transitions: Minimization of Coupling
Loss
n(active) > n(passive)
small length Þ material loss ß
large length Þ radiation loss ß

38. Fabrication Lower Electrode Vertical Slope Upper Coatings
first a lower electrode is deposited on the lower cladding material
then both the passive and active core layers are spin cast, and a vertical slope is etched down through the active core material. The active core is next corona poled and crosslinked to vertically align the nonlinear molecules and created a noncentrosymmetric active material.
next using standard photolithography and reactive ion etching techniques, a ridge is etched throughout the entire structure. This creates a ridge only in the core layer where guiding is desired.
the final steps include spin casting the upper cladding material and depositing the upper electrode.
to create this vertical etch, we used an unconventional reactive ion technique.
Upper Coatings
Waveguide Ridge

39. 3-D Modulators
first a lower electrode is deposited on the lower cladding material
then both the passive and active core layers are spin cast, and a vertical slope is etched down through the active core material. The active core is next corona poled and crosslinked to vertically align the nonlinear molecules and created a noncentrosymmetric active material.
next using standard photolithography and reactive ion etching techniques, a ridge is etched throughout the entire structure. This creates a ridge only in the core layer where guiding is desired.
the final steps include spin casting the upper cladding material and depositing the upper electrode.
to create this vertical etch, we used an unconventional reactive ion technique.

40. Vertical Integration of EO Circuitry with VLSI Electronics

41. Vertical Integration of EO Circuitry with VLSI Electronics

42. Vertical Integration of EO Circuitry with VLSI Electronics

43. IMPROVED PROCESSABILITY: POLYMER MICRO-PHOTONIC RING RESONATORS
Integrated wavelength add-drop filter
l1, l2, l3
Re-configurable optical waveguide cross connect.
The streets and avenues are fabricated on
different levels with the ring resonator switches
in between at each junction.
WDM modulation module.
Each wavelength modulated by
separate resonate modulator.
Laser
l1, l2, l3
Modulates l1
Modulates l2
Modulates l3

44. POLYMER MICRO-PHOTONIC RING RESONATOR USING ELECTRO-OPTIC POLYMERS
GND
Au upper modulation
electrode
Complementary
modulated output
Input
Modulated output
5mm
4.5mm
3mm Si
UV15
CLD1
SU-8
UFC 170 Au
CROSSECTION
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)

45. INTEGRATED WDM TRANSMITTER-RECIEVER
Au Electrode
SU-8
Gold ground
GND
Eye diagram
1 Gb/s, Vpeak = 1 V
Device has ~2GHz BW
= 2 GHz/V

46. Large Angle, Fast Response Spatial Light Modulator (SLM)
Schematic Diagram
Experimental Results
Literature Citations
• Dalton, Steier, et al., “Polymeric waveguide prism based electro-optic beam deflector,” Opt. Eng., 40, (2001)
• Dalton, Steier, et al., “Beam deflection with electro-optic polymer waveguide prism array,” Proc. SPIE, 3950, (2000)
• Dalton, Steier, et al., “Polymeric waveguide beam deflector for electro-optic switching,” Proc. SPIE, 4279, (2001)
Large angle (± 70 degree) laser beam steering is demonstrated. In the upper left part of the figure is shown the schematic diagram of the final device. Beam steering is initiated by a cascaded prism array. The effective interaction length of light and the applied electrical field is the length of the base of the cascaded prism array. This is experimentally observed and consistent with theoretical simulation. Beam steering is then amplified by a partial photonic bandgap structure. The amplification factor is 10. The observed experimental result is shown in the upper right. Large angle beam steering is achieved with nearly six orders of magnitude improvement in switching speed relative to liquid crystal spatial light modulators (with comparable drive voltages). The lower right part of the figure shows the holographic photoprocessing of the organic partial photonic bandgap lattice. In the lower right part of the figure, citations to publications dealing with this device are given. Other articles are in press.
Photonic Band Gap Fabrication

47. Phased Array Radar with Photonic Phase Shifter (1 of 3 approaches)
Dalton, Steier, Fetterman, et al., IEEE mW & Guided Wave Lett., 9, 357 (1999)

48. High Bandwidth, Ultrastable Oscillators (Signal Generators)
• Dalton, Steier, Fetterman, et al., “Photonic control of terahertz systems,” Terahertz Electronic Proceedings, (1998)
• Dalton, Steier, Fetterman, et al., “Electro-optic applications,” in Encyclopedia of Polymer Science and Technology (J. Kroschwitz, ed) Wiley & Sons, NY, 2001

49. 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).

50. High Bandwidth Optical Modulators
and Switches (The Electrical Problem)
Two bands approach:
• DC-65 GHz direct modulation, use one modulator section;
• 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, (2000).

51. HYBRID INTEGRATION POLYMER
PHOTONIC MODULE 4
Electro-optic SSB modulator
Si Electronics
Low loss passive guide
Electro-optic guide
Amplifying guide
l1, l2, l3
l filter
EO phase shifter
Amplifier
OBJECTIVE – Develop photonic modules which integrate multiple waveguide
devices and Si electronics into single package.
APPROACH – Use 3D integration concepts to integrate different photonic polymers
into single photonic circuit. Use adiabatic coupling in tapered guides for low loss
coupling between various materials. Fabricate polymer devices on top of processed
Si integrated electronics. Reduce fiber coupling loss by symmetric design of
passive waveguides