IEEE Journal of Quantum Electronics - Electrical and Computer ...

IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 36, NO. 5, MAY 2000

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Optical Intensity Modulator Based on a Novel Electrooptic Polymer Incorporating a High Chromophore Sang-Shin Lee, Sean M. Garner, Vadim Chuyanov, Hua Zhang, William H. Steier, Fang Wang, Larry R. Dalton, Anand H. Udupa, and Harold R. Fetterman

Abstract—We have synthesized a novel electrooptic (EO) polymer based on a high chromophore incorporating tricyanobutadiene acceptors. A crosslinked polyurethane network was also adopted to enhance its thermal stability. In order to find the optimum poling condition for the polymer, the influence of the electric poling profile on optical characteristics such as EO effect, thermal stability, and damage was investigated. Then a high-speed intensity modulator using the EO polymer was designed and fabricated. The measured half-wave voltage V was 4.5 V at the wavelength of 1.31 m. Accordingly, the achieved EO coefficient r33 was as high as 25 pm/V, and the thermal stability of the poled polymer was as high as 95 C. Finally, the modulator was successfully operated up to 40 GHz. Index Terms—Electrooptic modulation, fiber optics, optical planar waveguide components, optical polymers, optical waveguides.

I. INTRODUCTION IGH-SPEED optical intensity modulators have been widely used in analog fiber-optic transmission systems, community access television (CATV) distribution systems, radio frequency (RF) phase shifters, and analog/digital microwave links [1], [2]. They are also attractive as an external modulator in wavelength division multiplexing (WDM) fiber-optic telecommunication systems [3]. Recently, electrooptic (EO) polymers attracted extensive attention due to their advantages over inorganic materials. The first advantage is the low dispersion in the index of refraction between infrared and millimeter-wave frequencies. The second is that they can be deposited onto and will adhere to many substrates including semiconductors. In addition, optical guiding structures and modulators or optical switches use fabrication techniques that are compatible with semiconductor electronics. This makes possible a significant step forward in optoelectronic integration. The third advantage is the ability to integrate the active polymer

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Manuscript received November 10, 1999; revised February 3, 2000. S.-S. Lee was with the Department of Electrical Engineering-Electrophysics, University of Southern California, Los Angeles, CA 90089-0483 USA. He is now with the Devices and Materials Laboratory, LG Corporate Institute of Technology, Seoul 137-724, Korea. S. M. Garner, V. Chuyanov, H. Zhang, and W. H. Steier are with the Department of Electrical Engineering-Electrophysics, University of Southern California, Los Angeles, CA 90089-0483 USA. F. Wang and L. R. Dalton are with the Department of Chemistry, University of Southern California, Los Angeles, CA 90089 USA. A. H. Udupa and H. R. Fetterman are with the Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, CA 90095 USA. Publisher Item Identifier S 0018-9197(00)03540-5.

materials into an optical circuit, which includes other optical materials. So far, high-speed EO polymer modulators operating up to 110 GHz have been demonstrated [4]–[6]. For practical systems applications, the polymer modulators are required to have lower half-wave voltage V , higher thermal stability, and lower loss. The V of the polymer modulators can be reduced by using an EO polymer based on chromophores with a high molecular nonlinearity ( ). Here is the permanent dipole moment in the ground state and is the first molecular hyperpolarizability, and so the value is proportional to the EO coefficient of the polymer. Also, the thermal stability can be enhanced remarkably by using a crosslinkable system instead of the guest-host or side-chain systems, since the backbone and chromophore of the crosslinkable polymer are chemically crosslinked to make the relaxation of the aligned chromophores difficult. Recently, Shi et al. reported a modulator based on a Polyurethane Disperse Red (DR) 19 thermoset polymer [7]. In this paper, we have synthesized a new high chromophore, FTC, by using a novel tricyanobutadiene acceptor incorporating a furan-derative ring. Its value (15 000210048 esu at 1.06 m) is larger than that of previous chromophores like DR1 (580210048 esu) [8], DR19, and DANS [9] by one order. Then a functionalized FTC was formed to synthesize a thermal crosslinkable EO polymer, PU-FTC. In order to find the near optimum poling condition for the new crosslinkable polymer, the influence of the electric poling profile on the optical characteristics such as EO effect, thermal stability, and damage was investigated. Finally, we have successfully demonstrated a high-speed optical intensity modulator. II. SYNTHESIS OF A NEW CROSSLINKABLE EO POLYMER Recently, we developed a high choromophore based on a novel tricyanobutadiene acceptor incorporating a furan-derivative ring, FTC (2-dicyanomethylen-3-cyano-4-f2-[trans-(4-N, N-diacetoxyethyl-amino) phenylene-3,4-dibutylthien-5]vinyl g5,5-dimethyl-2,5-dihydrofuran) [10]. Fig. 1 shows the synthesis procedure for the PU-FTC polymer using the FTC chromophore. The furan ring plays an important role in keeping the conjugation planar and stabilizing the acceptor end of the chromophore. Also, the two methyl groups on the heterocyclic (oxygen) ring and the two butyl groups on the thiophene ring should prevent the large dipolar chromophores from aggregating, which is caused by strong electrostatic interactions in most of the high chromophores. The interaction between

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Fig. 1. The FTC chromophore and the covalent incorporation into a thermal-set polyurethane polymer to from the PU-FTC polymer. TDI and TEA are commercially available crosslinkers and dioxane is the solvent used.

the chromophores may reduce the achievable EO coefficients. The FTC chromophore when doped into a PMMA host has a r33 value of 55 pm/V @ 1.06 m. The chromophore has excellent solubility essential for materials processibility, high chromophore thermostability (>300 C), and the guest–host system has a modest optical loss of 1 dB/cm @ 1.3 m. In this work, to enhance the thermal stability of the PMMA- doped FTC, we have synthesized hydroxyl functionalized FTC chromophores by adopting a single-end crosslinked polyurethane system, because the thermoset polyurethanes have been widely used to stabilize the polar alignment of a nonlinear optic polymer. The FTC chromophore is mixed with toluene diisocyanate (TDI) in a solvent and heated to attach the NCO groups to the OH groups. Next, the crosslinker, triethanolamine (TEA), is added which acts to form a 3-D network during the pre-curing and final hardening during poling. Excess TDI and TEA can be added to control the density of chromophores.

Fig. 2. The absorption spectrum of the PU-FTC polymer.

III. CHARACTERIZATION OF THE PU-FTC POLYMER The basic optical properties of the PU-FTC polymer have been observed first. The absorption spectrum of the polymer was measured with a spectrophotometer, and Fig. 2 shows the absorbance as a function of the wavelength. The absorption peak is at 670 nm, and the absorption beyond = 1000 nm is negligibly small. Also, the propagation loss of the polymer was measured by employing the liquid out-coupling method [11]. A thin polymer film was prepared on a silicon substrate coated with a 4-m-thick SiO2 layer to form a planar waveguide structure, and light was prism-coupled into it. After propagating over a distance in the polymer layer, the light was coupled from the polymer film to a high index liquid into which the waveguide was dipped. The attenuation of the light as a function of the propagation distance was obtained to provide the propagation loss of 2 dB/cm @ 1.3 m. Then, the poling characteristics of the PU-FTC were studied to find the near optimum poling condition leading to large EO coefficients without damage. For the electric field-assisted

Fig. 3. The electric poling temperature and voltage profiles for the PU-FTC polymer.

poling, which is used to align the chromophores for achieving the EO effect, we adopted the corona poling method. The typical needle-to-plane distance was about 2 cm and the dc voltage applied to the needle was 8 kV. The poling schedule for the thermosetting polymer was designed to achieve a large EO effect and high thermal stability without causing damage. Fig. 3

LEE et al.: OPTICAL INTENSITY MODULATOR BASED ON A NOVEL ELECTROOPTIC POLYMER

Fig. 4. EO coefficients of the poled polymer as a function of the pre-curing time.

shows the typical electric poling profile, which consists of two steps, pre-curing and actual poling. During the pre-curing step, the crosslinkable nonlinear optical polymer, PU-FTC, is heated for slight hardening to temperature Tpre for the time tpre to initiate partial crosslinking prior to applying the high voltage. This is to prevent surface damage due to the electric charges induced by the corona needle during poling. There is a tradeoff between the pre-curing and the poling efficiency. When the pre-curing is not sufficient, surface damage occurs, while with excessive pre-curing the rotation of the chromophores is restricted and the poling efficiency is reduced. Then, during the actual poling step, a dc voltage Vp is applied to the corona needle with the film temperature fixed at Tp , so that the aligning of the chromophores and the crosslinking of the polymers is completed. Here again there is a tradeoff. Higher Tp may allow easier rotation of the chromophores and allow more complete crosslinking, which gives higher poling efficiency and higher thermal stability. On the other hand, if Tp is too high, the crosslinking may be achieved before the chromophores have had time to align to the electric field. The optical characteristics of the poled polymers were measured in terms of the EO coefficient r33 , thermal stability, and damage. First, the effect of the pre-curing time on r33 and surface damage was examined. Five thin PU-FTC films were prepared on glass substrates coated with indium–tin–oxide (ITO) and dried overnight in a vacuum oven. They were corona-poled on a hot plate by varying the pre-curing time from 0 to 20 min, with the pre-curing temperature fixed at 120 C. The actual poling temperature and time were fixed at 110 C and 1 h, respectively. The value of r33 of the poled polymers was measured by using the attenuated total reflection (ATR) method [12]. Fig. 4 shows r33 at 1.06 m as a function of the pre-curing time tpre . The film with no pre-curing was severely damaged due to insufficient crosslinking and did not provide any EO effect. However, the films with the tpre of longer than 3 min were not damaged, indicating that they became rigid and crosslinked enough to resist the ion bombardment of the charges. As shown in Fig. 4, the r33 decreases with the pre-curing time. This is because, as the pre-curing progresses, the polymer network gradually gets crosslinked. Therefore, the mobility of the chromophores is reduced to yield smaller alignment of the dipoles. The EO coefficient of the PU-FTC is mostly smaller than that of the PMMA-doped FTC. This is

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(a)

(b) Fig. 5. SEM photographs of the poled PU-FTC polymer films. (a) With no damage. (b) With damage.

attributed to the lower poling efficiency of the attached PU-FTC where the chromophores have less freedom than those in the doped systems. It is noted that, for the thermosetting material, lattice hardening is taking place during poling and can reduce poling efficiency by preventing some of the chromophore from reorienting under the influence of the poling filed. Fig. 5(a) and (b) show the SEM photographs of the undamaged and damaged films, respectively. The poling-damaged film reveals serious surface deformation such as irregular holes, which will cause serious scattering loss, while the film with no damage has an optically flat surface. The deformation is attributed to the strong compressive electrostatic force of the charges accumulated on the film, since the charged particles may carry large kinetic energy when they pass through the high electric potential between the corona needle and the ground electrode. Then, the effect of the actual poling temperature on the thermal stability, EO coefficient, and poling damage was studied. Five polymer films were pre-cured at 120 C for 3 min and then poled by varying the poling temperature from 80 C to 120 C. The thermal stability of the poled polymer was measured with the in situ second harmonic generation (SHG) temperature ramping method [13]. We applied current through the ITO to ramp up the temperature of the poled samples, while monitoring the SHG signal out of them. The thermal stability was obtained by finding the temperature at which the SHG signal began to be decreased since the alignment of the

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Fig. 6. SHG coefficients of the poled PU-FTC polymer as a function of the temperature.

Fig. 8. Structure of the Mach–Zehnder intensity modulator based on the PU-FTC.

Fig. 7. Thermal stability temperatures and EO coefficients of the poled PU-FTC polymer as a function of the poling temperature.

chromophores was randomized. Fig. 6 shows the normalized SHG coefficients d33 as a function of the temperature for the sample poled at 100 C. Tstab can be obtained by finding the temperature at which the linear lines used for fitting the two curves with distinct slopes are intersected. As shown in Fig. 6, the nonlinear optic effect of the poled PU-FTC remains stable up to the Tstab of 95 C. Also, Fig. 7 shows the thermal stability temperature Tstab and the r33 as a function of the actual poling temperature. As shown in the figure, Tstab is heightened when the poling temperature increases from 80 C to 100 C. However, it is saturated at about 95 C for poling temperatures beyond 100 C, because the crosslinking density of the polymer chains is limited. When the poling temperature increases, the crosslinking density is increased to a certain extent, but then limited since the uncrosslinked polymer chains cannot find the partners for crosslinking any more. The film poled at 120 C was severely damaged like the damaged film shown in Fig. 5(b), since it was too soft at that high temperature. Fig. 7 also shows r33 versus the poling temperature. r33 is as small as 8 pm/V for the Tp of 80 C, and it has been increased up to 40 pm/V for the Tp of 100 C due to the enhanced mobility of the chromophores. The r33 value @ 1.3 m corresponding to that of 40 pm/V @ 1.06 m was estimated to be about 25 pm/V by using the two-level model [14]. However, it is saturated for the Tp of >100 C. This indicates the saturation of the poling efficiency: the mobility of the chromophores increases with the poling temperature, but it is finally limited since the reaction speed for crosslinking is also increased with the temperature. Finally, the poling efficiency of the PU-FTC polymer coated on top of a lower cladding was considered, because for a practical device the electric poling is done across the two polymer layers. A thermal crosslinkable epoxy, Epoxylite 9653, was

chosen for the lower cladding. We have prepared two samples, a single PU-FTC layer and a PU-FTC layer stacked on the lower cladding. The two samples were poled by using the same poling profile, and the SHG signals from them were measured and compared. There was no significant difference in the SHG signals between the two samples. Therefore, it was confirmed that the PU-FTC polymer could be efficiently poled regardless of the lower cladding. IV. DESIGN OF THE POLYMER MODULATOR The high-speed Mach–Zehnder intensity modulator based on the proposed PU-FTC is shown in Fig. 8. It combines a traveling wave optical Mach–Zehnder interferometer and a traveling wave microstrip line circuit. First, for vertical confinement in the optical waveguide, a triple stack structure composed of the lower cladding, core EO polymer (n = 1:65 @ 1.3 m), and upper cladding was fabricated. A thermally curable epoxy, Epoxylite 9653 (n = 1:54 @ 1.3 m), was used for the lower cladding. It was experimentally confirmed, as mentioned earlier, that the epoxy has a lower bulk resistivity than PU-FTC, which facilitates the electric field poling. A UV curable epoxy, NOA73 (n = 1:54 @ 1.3 m), was chosen for the upper cladding. In the typical device, the waveguide rib width was 6 m, the core layer thickness was 1.5 m, and the rib height was 0.3 m. The thickness of the lower and upper claddings was set at 3 m and 3.5 m, respectively, to keep the optical loss due to the electrodes small. The length of the arms of the interferometer where the modulation interaction occurs was 20 mm and the length of the linear Y -branch transition was 3 mm at each side. The total branching angle of the Y -branch was 1 , and the separation between the two straight waveguides in the interaction region was 50 m. For the traveling-wave type microwave electrode, a microstrip line (MSL) structure was adopted. Its characteristic impedance was designed to be 50 by setting the width of the upper electrode to be 22 m, with a typical electrode gap of 10 m. A smaller electrode gap results in a lower driving voltage. However, this could cause higher microwave loss due to the ohmic loss. To reduce the mm-wave loss, the thickness of the upper electrode was increased to 4 m by electroplating after the electrode shape was defined by lithography. Then the extra loss due to both the bends and the transitions from the

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broad pad to the narrow MSL was considered. It was found that a simple right-angle bend could be used without any significant radiation loss. A tapered pad structure, 3 mm2150 m, was formed at each end of the microstrip line to facilitate the attachment of the coaxial input and output cables during packaging. V. DEVICE FABRICATION AND EXPERIMENTAL RESULTS The fabrication steps for the EO polymer modulator are described here. The bottom ground electrode was made on a silicon substrate by depositing Cr/Au. For the lower cladding, Epoxylite 9653 was spin-coated to be 3 m and thermally cured by heating at 130 C for 3 h. For the core layer, a 1.5-m-thick PU-FTC was spun and dried overnight, and then pre-cured at 120 C for 3 min on a hot plate. To induce the EO effect in the core, corona poling was performed at 100 C by applying 8 kV between the corona needle and the ground electrode. Then, a standard photolithography and RIE in oxygen were done to form the core rib for the waveguide. NOA73 was spin-coated to be 3.5 m for the upper cladding and cured by exposing under ultraviolet light. Thin Cr/Au layers were deposited on top of the polymer films as base metals for the electroplating, and a photoresist 8 m thick was spun on the metal layers and dried sufficiently at room temperature. Also, we have made the electrode pattern by aligning the electrode pattern on the mask with the etched waveguide pattern. Electroplating was performed at 50 C for 10 min with a pulsed current source. The thickness and width of the electrode are 4 m and 22 m, respectively. Finally, for light coupling, the end facets were prepared by dicing with a nickel blade. To measure the performance of the modulator, TM-polarized light at 1.31 m was coupled to the device through a single-mode fiber. The output light was collected by an objective lens and focused onto a photodetector. Fig. 9 shows the response of the modulator to a low-frequency sawtooth wave electrical signal. The upper signal is the applied modulating signal and the lower the optical output. V is obtained by finding the voltage required to turn the modulator from full on to full off. The measured V was 4.5 V, which corresponds to an r33 of about 25 pm/V with an effective field-overlap integral factor of one. This is consistent with the r33 value measured at 1.06 m on test samples. The extinction ratio, the ratio of the light power out during the on state to that of the off state, was measured to be 18 dB. The extinction ratio should increase when a single-mode fiber is used to collect the output rather than the lens. The measured insertion loss was 14 dB for the device length of 36 mm. The total insertion loss is the sum of the waveguide propagation loss and the coupling loss at the facets. There is a 5-dB/facet coupling loss since no attempt was made to match the 9-m-diameter mode of the fiber to the elliptical mode (7 m2 2 m) of the polymer waveguide. Accordingly, the propagation loss of the waveguide was 2.5 dB/cm. The waveguide propagation loss is a collection of the losses from material intrinsic absorption, waveguide/cladding layer scattering, and poling-induced scattering [15]. Finally, Fig. 10 shows the frequency response of the modulator. The device is working well from 0 to 40 GHz except for some

Fig. 9. Oscilloscope traces for the measurement of V of the polymer modulator. The upper trace is the 10 Vp-p , 1-kHz sawtooth waveform applied to the microstrip line. The lower trace is the light output from the device.

Fig. 10. The measured frequency resoponse of the PU-FTC Mach–Zehnder modulator.

ripples, which are believed to be due to impedance mismatches at the input and output. VI. CONCLUSIONS A novel crosslinkable EO polymer based on a high chromophore incorporating tricyanobutadiene acceptors was proposed and synthesized. We have systematically studied the effect of the electric poling profile on optical characteristics such as the EO effect, thermal stability, and damage, in order to realize the optimum poling condition leading to a large EO coefficient and high thermal stability. Also, a high-speed intensity modulator was successfully designed and fabricated by employing the polymer and a near optimum poling scheme. REFERENCES [1] G. E. Betts, “Linearized modulators for suboctave-bandpass optical analog links,” IEEE Trans. Microwave Theory Tech., vol. 42, pp. 2642–2649, 1994. [2] S.-S. Lee, A. H. Udupa, H. Erlig, H. Zhang, Y. Chang, C. Zhang, D. H. Chang, D. Bhattacharya, B. Tsap, W. H. Steier, L. R. Dalton, and H. R. Fetterman, “Demonstration of a photonically controlled RF phase shifter,” IEEE Microwave Guided Wave Lett., vol. 9, pp. 357–359, 1999. [3] A. R. Chraplyvy, J.-M. Delavaux, R. M. Derosier, G. A. Ferguson, D. A. Fishman, C. R. Giles, J. A. Nagel, B. M. Nyman, J. W. Sulhoff, R. E. Tench, R. W. Tkach, and J. L. Zyskind, “1420-km transmission of sixteen 2.5-Gb/s channels using silica-fiber-based EDFA repeaters,” IEEE Photon. Technol. Lett., vol. 6, pp. 1371–1373, 1994. [4] C. C. Teng, “Travelling-wave polymeric optical intensity modulator with more than 40 GHz of 3-dB electrical bandwidth,” Appl. Phys. Lett., vol. 60, pp. 1538–1540, 1992. [5] Y. Shuto, S. Tomaru, M. Hikita, and M. Amano, “Optical intensity modulators using diazo-dye-substituted polymer channel waveguides,” IEEE J. Quantum Electron., vol. 31, pp. 1451–1460, 1995. [6] D. Chen, H. R. Fetterman, A. Chen, W. H. Steier, L. R. Dalton, W. Wang, and Y. Shi, “Demonstration of 110 GHz electro-optic polymer modulators,” Appl. Phys. Lett., vol. 70, pp. 3335–3337, 1997.

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[7] Y. Shi, W. Wang, J. H. Bechtel, A. Chen, S. Garner, S. Kalluri, W. H. Steier, D. Chen, H. R. Fetterman, L. R. Dalton, and L. Yu, “Fabrication and characterization of high-speed polyurethane-disperse red 19 integrated electrooptic modulators for analog system applications,” IEEE J. Select. Topics Quantum Electron., vol. 2, pp. 289–299, 1996. [8] S. Matsumoto, K. Kubodera, T. Kurihara, and T. Kaino, “Nonlinear optical properties of an azo dye attached polymer,” Appl. Phys. Lett., vol. 51, pp. 1–2, 1987. [9] E. V. Tomme, P. P. V. Daele, R. G. Baets, and P. E. Lagasse, “Integrated optic devices based on nonlinear optical polymers,” IEEE J. Quantum Electron., vol. 27, pp. 778–787, 1991. [10] F. Wang, A. S. Ren, M. He, Q. W. Harper, L. R. Dalton, S. M. Garner, H. Zhang, A. Chen, and W. H. Steier, “High electro-optic coefficient from a polymer containing high chromophores,” presented at the ACS Polymer Materials Science and Engineering Conf., Dallas, TX, 1998. [11] C. C. Teng, “Precision measurements of the optical attenuation profile along the propagation path in thin-film waveguides,” Appl. Opt., vol. 32, pp. 1051–1054, 1993. [12] D. Morichere, P. A. Chollet, W. Fleming, M. Jurich, B. A. Smith, and J. D. Swalen, “Electro-optic effects in two tolane side-chain nonlinear-optical polymers: Comparison between measured coefficients and second harmonic generation,” J. Opt. Soc. Amer. B., vol. 10, pp. 1894–2000, 1993. [13] M. Eich, A. Sen, H. Looser, G. C. Bjorklund, J. D. Swalen, R. Twieg, and D. Y. Yoon, “Corona poling and real-time second-harmonic generation study of a novel covalently functionalized amorphous nonlinear optical polymer,” J. Appl. Phys., vol. 66, pp. 2559–2567, 1989. [14] J. L. Oudar and D. S. Chemla, “Hyperpolarizabilities of the nitroanilines and their relations to the excited state dipole moment,” J. Chem. Phys., vol. 66, pp. 2664–2668, 1997. [15] C. C. Teng, M. A. Mortazavic, and G. K. Boudoughian, “Origin of the poling-induced optical loss in a nonlinear optical polymeric waveguide,” Appl. Phys. Lett., vol. 66, pp. 667–669, 1995.

Sang-Shin Lee was born in Korea on September 5, 1968. He received the B.S., M.S., and Ph.D. degree in electrical engineering from Korea Advanced Institute of Science and Technology, Taejon, in 1991, 1993, and 1997, respectively. From 1997 to 1998, he worked as a Post-Doctoral Research Associate at the University of Southern California, Los Angeles. In 1998, he joined the Devices and Materials Laboratory of LG Corporate Institute of Technology, Seoul, Korea. His current research interests include polymer waveguide devices like modulators, switches, and variable optical attentuators, and optical MEMS devices.


Sean M. Garner received the B.E. degree in engineering physics from Stevens Institute of Technology, Hoboken, NJ, in 1993 and the Ph.D. degree in electrical engineering from the University of Souther California, Los Angeles, in 1998. Since 1998, he has been a Senior Research Scientist at Corning Incorporated, and his current research interests include optical waveguide devices.

Vadim Chuyanov, photograph and biography not available at the time of publication.

Hua Zhang was born in China in 1970. He received the B.S. degree in communication engineering from the University of Electronic Science and Technology of China in 1993 and the M.S. degree in electronic engineering from the University of Science and Technology of China in 1996. He is currently working toward the Ph.D. degree at the Department of Electrical Engineering of the University of Southern California, Los Angeles. His research interests are mainly in integrated nonlinear optical devices.

William H. Steier, photograph and biography not available at the time of publication.

Fang Wang, photograph and biography not available at the time of publication.

Larry R. Dalton, photograph and biography not available at the time of publication.

Anand H. Udupa was born in Chennai, India, in 1976. He received the B.Tech. degree from the Indian Institute of Technology, Chennai, in 1997, and the M.S. degree in electrical engineering from the University of California, Los Angeles, in 1999. His graduate research focused on the design and testing of high-frequency polymer modulators. He co-authored many scientific papers in international journals and conferences. He currently works in the field of mixed signal circuit design at Texas Instruments, Bangalore, India.

Harold R. Fetterman, photograph and biography not available at the time of publication.