ONO2000 Tutorial

1. OUTLINE: ONO2000Tutorial INTRODUCTION --The phenomena of optical nonlinearity --Voltage dependent index of index of refraction --Simple Devices CHROMOPHORES --Optimizing hyperpolarizability -- Auxiliary Properties MATERIALS --Optimizing electro-optic activity --Theory and optimized design of chromophores --Optical Loss --Lattice Hardening PROCESSING --Fabrication of buried channel wavguides --Tapered and vertical transitions --Fabrication of 3-D integrated circuits DEVICES AND PERFORMANCE --Prototype devices and performance evaluation --Advanced devices (e.g., phased array radar) FUTURE PROGNOSIS REFERENCES

2. INTRODUCTION: Linear and Nonlinear Polarization ONO2000Tutorial

3. INTRODUCTION: Tensor Properties of c(2) ONO2000Tutorial

4. INTRODUCTION: Frequency Dependence of Polarization ONO2000Tutorial For a sinusoidal field, E(z,t) = E0cos(wt-kz) the polarization becomes:

5. INTRODUCTION: Frequency Dependence of Index of Refraction ONO2000Tutorial

6. INTRODUCTION: The Electro- Optic Coefficient ONO2000Tutorial

7. INTRODUCTION: Useful Relationships ONO2000Tutorial Relationship of phase shift to EO coefficient and applied field Relationship of Vp voltage to EO coefficient where l is the free-space wavelength, d is the thickness of the waveguide core and cladding, L is the length of the electrode. Applied electric field is now denoted by V rather than E. Voltage Length Product Figure of Merit where e is the dielectric constant

8. INTRODUCTION: Comparison of Organic and Inorganic Materials ONO2000Tutorial

9. INTRODUCTION: Comparison of Organic and Inorganic Materials ONO2000Tutorial Stability will vary depending how the final polymeric EO material is prepared. Trace 1, guest/host composite; Traces 2-4, chromophores in hardened polymers. Trace 3 corresponds to DEC shown below. Trace 5 corresponds to sol-gel glass. Circles denote an IBM polymer with the DANS chromophore covalent attached by one end to PMMA. DEC refers to a double end crosslinked chromophore prepared by Dalton, et al.

10. INTRODUCTION: Simple Device Configurations ONO2000Tutorial Mach Zehnder Modulator Birefringent Modulator Directional Coupler

11. INTRODUCTION: Mach Zehnder Modulator and Simple Device Performance Comparison ONO2000Tutorial Comparison of key features of simple devices Mach Zehnder Birefringent Directional InterferometerModulatorCoupler reff r33 r33-r13 r33 Vp VpMZ 1.5 VpMZ 1.73 VpMZ Mod. PMZ 2.75 PMZ 3 PMZ Power

12. CHROMOPHORES: Charge- Transfer (Dipolar Chromophores) ONO2000Tutorial With the exception of octupolar chromophores (which we will not discuss) electro-optic chromophores are dipolar charge- transfer molecules consisting of donor, bridge, and acceptor segments. They are by nature modular materials (see below).

13. CHROMOPHORES: Optimizing Chromophore Hyperpolarizability ONO2000Tutorial The two level model has provided useful guidance in optimizing molecular hyperpolarizability, b. where weg is the frequency of the optical transition, f is the oscillator strength, Dm is the difference between the ground and excited state dipole moments. Through this relationship, b can be related to material properties such as bond length alternation, BLA, and to donor and acceptor strength.

14. CHROMOPHORES: Variation of mb with Molecular Structure ONO2000Tutorial The simple two level model and structure/function insight gained from the model has permitted a dramatic improvement in molecular hyperpolarizability (see below). In the limit of non- interacting chromophores, electro-optic activity (induced by electric field poling) scales as Nmb (where N is number density and m is dipole moment); thus, we list mb instead of b. In the 1990s, an improvement of a factor of 40 was achieved.

15. CHROMOPHORES: Auxiliary Properties--Thermal Stability ONO2000Tutorial Thermal stability depends on host matrix (see below) and atmosphere (packaging). Typically defined as temperature at which EO activity is first observed to decrease.

16. CHROMOPHORES: Auxiliary Properties--Thermal Stability ONO2000Tutorial Good thermal stability and molecular hyperpolarizability are not mutually exclusive (see example below)

17. CHROMOPHORES: Auxiliary Properties--Purity ONO2000Tutorial Ionic impurities can lead to ionic conductivity during electric field poling. This can reduce the field felt by chromophores and poling efficiency.

18. CHROMOPHORES: Summary ONO2000Tutorial Chromophore Requirements: •Large hyperpolarizability and large dipole moment •No absorption at operating wavelength •Stability --Thermal --Chemical & Electrochemical --Photochemical •Solubility in spin casting solvents •Compatibility with polymer hosts (particularly for guest/host materials) •Low volatility (particularly if used for guest/host materials with high Tg polymer)

19. CHROMOPHORES: Dipole Moments ONO2000Tutorial Chromophore dipole moments will be very useful for understanding the translation of microscopic optical non- linearity to macroscopic electro-optic activity. Below we show dipole moments calculated for representative EO chromophores using SpartanTM

20. MATERIAL ISSUES: Translating Molecular Optical Nonlinearity to Macroscopic Electro-Optic Activity ONO2000Tutorial EO coefficient is not a simple linear function of chromophore loading. Curves exhibit a maximum. Why?

21. MATERIALS ISSUES: Optimizing Material Electro-Optic Activity-- Dependence on Chromophore Shape ONO2000Tutorial Data are shown for two different structures of the same chromophore: With isophorone groups (circles) and without isophorone protection of the polyene bridge (diamonds)

22. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Variation with Chromophore Structure ONO2000Tutorial Electro-optic coefficients for 4 different chromophores (FTC, squares; CLD,diamonds; GLD, circles; and CWC, crosses) are shown as a function of chromophore number density in PMMA. The dipole moments for these chromophores were shown in a previous overhead. 1 r33 pm/V 1

23. MATERIAL ISSUES: Optimizing Electro-Optic Activity: Theory-- Equilibrium Statistical Mechanics ONO2000Tutorial Electro-optic activity can be calculated according to r33 = 2NbF(w)<cos3q>/n4 The order parameter is where U = U1 + U2 is the potential energy describing the interaction of chromophores with the poling field (U1) and with each. For non-interacting chromophores, U = -mFcosq where F is the poling field felt by the chromophore. For this case, <cosnq>is Ln is the nth order Langevin function and f = |mF/kT| Consider chromophores interacting through a mean distance, r, which is related to number density by N = r-3. Let us follow Piekara and write the effective field at a given chromophore from surrounding chromophores as U2 = -Wcos(q2). The position w.r.t. the poling field is defined by Euler angles, W1 = {q1,f1} and the angles. or

24. MATERIAL ISSUES: Optimizing Electro-Optic Activity: Theory-- Equilibrium Statistical Mechanics ONO2000Tutorial Averaging is done over the two variables W and W2. Explicitly, The total potential is taken as -fcos(q) -Wcos(q2). In the high temperature approximation, exp(-U1/kT) = 1-fcos(q1). These integrals can be done analytically with the result

25. MATERIAL ISSUES: Optimizing Electro-Optic Activity ONO2000Tutorial Equilibrium statistical mechanical calculations are easily modified to take into account nuclear repulsive effects (by simply adjusting the integration limits). Below we show simulation data for a typical chromophore separating nuclear (shape) and intermolecular electronic effects.

26. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory ONO2000Tutorial Critical Conclusion: Chromophore shape is very important. Need to try to make chromophores more spherical. (Independent particle model) Comparison of Theory and Experiment for FTC

27. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory & Practice ONO2000Tutorial An example of modification of chromophore shape (CWC) to improve electro-optic activity is shown.

28. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory: Monte Carlo Methods ONO2000Tutorial Initially: No applied poling field, no intermolecular interactions Steps 1-400: Poling field on, no interactions Steps 400-800: Poling field and full interactions

29. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory: Monte Carlo Methods--Chromophore Distributions with Increasing Interactions ONO2000Tutorial Chromophore distributions are shown as a function of increasing chromophore concentration for concentrations of 1 x 1017/cc, 5 x 1020/cc, and 1.5 x 1021/cc.

30. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory: Monte Carlo Methods ONO2000Tutorial Variation of calculated electro-optic activity with number density is shown for different values of chromophore dipole moment.

31. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory: Comparison of Methods ONO2000Tutorial Comparison of Monte Carlo and equilibrium statistical mechanical (smooth and dashed lines) methods. Methods is shown below. Both methods predict same functional dependence on number density.

32. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory: Monte Carlo Methods ONO2000Tutorial The effect of chromophore shape on electro- optic activity is shown.

33. MATERIAL ISSUES: Optimizing Electro-Optic Activity--Theory: Phase Separation ONO2000Tutorial Theory can also be used to identify the conditions where phase separation (chromophore aggregation) occur. Phase separation will depend on applied electric field, chromophore concentration, and host dielectric constant. Curves 1-5 correspond to phase boundary lines for host dielectric constants of 2,3, 5,7, and 10. To the left is the homogeneous phase.