Technical documentation and specifics
Published Date: August 4, 2021
New paradigms in materials and devices for hybrid electro-optics and optical rectification
Abstract: We review recent transformative advances in materials design, synthesis, and processing as well as device engineering for the utilization of organic materials in hybrid electro-optic (EO) and optical rectification (OR) technologies relevant to telecommunications, sensing, and computing. End-to-end (from molecules to systems) modeling methods utilizing multi-scale computation and theory permit prediction of the performance of novel materials in nanoscale device architectures including those involving plasmonic phenomena and architectures in which interfacial effects play a dominant role. Both EO and OR phenomenon require acentric organization of constituent active molecules. The incumbent methodology for achieving such organization is electric field poling, where chromophore shape, dipole moment, and conformational flexibility play dominant roles. Optimized chromophore design and control of the poling process has already led to record-setting advances in electro-optic performance, e.g., voltage-length performance of < 50 volt-micrometer, bandwidths < 500 GHz, and energy efficiency < 70 attojoule/bit. They have also led to increased thermal stability, low insertion loss and high signal quality (BER and SFDR). However, the limits of poling in the smallest nanophotonic devices—in which extraordinary optical field densities can be achieved—has stimulated development of alternatives based on covalent coupling of modern high-performance chromophores into ordered nanostructures. Covalent coupling enables higher performance, greater scalability, and greater stability and is especially suited for the latest nanoscale architectures. Recent developments in materials also facilitate a new technology—transparent photodetection based on optical rectification. OR does not involve electronic excitation, as is the case with conventional photodiodes, and as such represents a novel detection mechanism with a greatly reduced noise floor. OR already dominates at THz frequencies and recent advances will enable superior performance at GHz frequencies as well.
- Johnson, L. E.; Elder, D. L.; Xu, H.; Hammond, S. R.; Benight, S. J.; O’Malley, K.; Robinson, B. H.; and Dalton, L. R.. Proc. SPIE 11812. 2021, Molecular and Nano Machines IV (1181202) , . Doi: https://doi.org/10.1117/12.2595638
Published Date: January 13, 2020
Ultrahigh Electro-Optic Coefficients, High Index of Refraction, and Long-Term Stability from Diels–Alder Cross-Linkable Binary Molecular Glasses
Abstract: The development of organic electro-optic (EO) materials that concurrently possess a high electro-optic coefficient (r33), high index of refraction, and long-term or high-temperature stability of chromophore alignment has been a crucial goal. To address this challenge, we developed a crosslinkable EO system consisting of two chromophores, HLD1 and HLD2, which can be electric field poled and then thermally crosslinked in situ to form a stable EO material. This approach avoids the necessity for nonlinear optically inactive materials such as polymers or small molecule cross-linkers, thus resulting in high chromophore density (>5 × 1020 molecules/cm3) and high index of refraction (n = 1.89 at 1310 nm) for HLD1/HLD2. Different ratios of HLD1 and HLD2 were evaluated to optimize poling efficiency and thermal stability of the poling-induced order. With 2:1 HLD1/HLD2 (wt/wt), a maximum r33 of 290 ± 30 pm/V was achieved in a cross-linked film. Thermal stability tests showed that after heating to 85 °C for 500 h, greater than 99% of the initial r33 value was maintained. This combination of large EO activity, high index of refraction, and long-term alignment stability is an important breakthrough in EO materials. HLD1/HLD2 can also be poled without the subsequent cross-linking step, and even larger maximum r33 (460 ± 30 pm/V) and n3r33 figure of merit (3100 ± 200 pm/V) were achieved. Hyperpolarizabilities of HLD and control molecules were analyzed by hyper-Rayleigh scattering and computational modeling with good agreement, and they help explain the high acentric order achieved during poling.
- Xu, H.; Liu, F.; Elder, D. L.; Johnson, L. E.; de Coene, Y.; Clays, K.; Robinson, B. H.; Dalton, L. R.. Chemistry of Materials. 2020, 32, 1408-1421. Doi: https://doi.org/10.1021/acs.chemmater.9b03725
Published Date: June 1, 2020
A monolithic bipolar CMOS electronic–plasmonic high-speed transmitter
Abstract: To address the challenge of increasing data rates, next-generation optical communication networks will require the co-integration of electronics and photonics. Heterogeneous integration of these technologies has shown promise, but will eventually become bandwidth-limited. Faster monolithic approaches will therefore be needed, but monolithic approaches using complementary metal–oxide–semiconductor (CMOS) electronics and silicon photonics are typically limited by their underlying electronic or photonic technologies. Here, we report a monolithically integrated electro-optical transmitter that can achieve symbol rates beyond 100 GBd. Our approach combines advanced bipolar CMOS with silicon plasmonics, and addresses key challenges in monolithic integration through co-design of the electronic and plasmonic layers, including thermal design, packaging and a nonlinear organic electro-optic material. To illustrate the potential of our technology, we develop two modulator concepts—an ultra-compact plasmonic modulator and a silicon-plasmonic modulator with photonic routing—both directly processed onto the bipolar CMOS electronics.
- Koch, U.; Uhl, C.; Hettrich, H.; Fedoryshyn, Y.; Hoessbacher, C.; Heni, W.; Baeuerle, B.; Bitachon, B. I.; Josten, A.; Ayata, M.; Xu, H.; Elder, D. L.; Dalton, L. R.; Mentovich, E.; Bakopoulos, P.; Lischke, S.; Krüger, A.; Zimmermann, L.; Tsiokos, D.; Pleros, N.; Möller, M.; Leuthold, J.. Nature Electronics. 2020, 3, 338–345. Doi: https://doi.org/10.1038/s41928-020-0417-9
Published Date: June 20, 2014
Benzocyclobutene barrier layer for suppressing conductance in nonlinear optical devices during electric field poling
Abstract: We measured the electro-optic (EO) coefficients (r33) of thin-film devices made from several monolithic, high number density organic EO chromophores with and without additional charge barrier layers. We found that a cross-linkable benzocyclobutene layer was very effective in suppressing unwanted, leakage current, keeping the effective poling voltage nearly identical to the applied voltage. This barrier layer proved to be superior to a titanium dioxide (TiO2) barrier layer. The suppression of the leakage current in combination with a new chromophore enabled the construction of EO devices that had r33 values in the range of 400–500 pm V−1 with poling fields ≥ 85 V μm−1.
- Jin, W.; Johnston, P. V.; Elder, D. L.; Tillack, A. F.; Olbricht, B. C.; Song, J.; Reid, P. J.; Xu, R.; Robinson, B. H.; Dalton, L. R.. Applied Physics Letters. 2014, 104, 243304. Doi: https://doi.org/10.1063/1.4884829
Published Date: March 18, 2016
Structure–function relationship exploration for enhanced thermal stability and electro-optic activity in monolithic organic NLO chromophores
Abstract: We have developed a series of novel monolithic materials based on molecules previously explored as dopants in guest–host systems to study intrinsic structure–function relationships in organic electro-optic (EO) materials. In a library of EO molecules with varied bridge segments, molecular modification of the donor with bis(tert-butyldiphenylsilyl) groups led to improvement in formation of amorphous films and led to enhanced poling efficiency. Further modification to include a carbazole site-isolation group on the bridge effectively reduced intermolecular dipole–dipole interactions, led to a material with poling efficiency of approximately 3 (nm V−1)2, and an increased glass transition temperature to 20–40 °C higher than similar reported monolithic materials. This level of thermal stability is comparable to common guest/host systems, which incorporated poly(methyl methacrylate) (PMMA) as the host. Our research showed that π-bridge length and type impacted first molecular hyperpolarizability β of a chromophore, which is accordingly reflected in the EO response. These findings further promote the utility of monolithic materials for their increased EO behavior and improved thermal stability, making this material system a competitor of guest–host systems in commercial applications.
- Jin, W.; Johnston, P. V.; Elder, D. L.; Manner, K. T.; Garrett, K. E.; Kaminsky, W.; Xu, R.; Robinson, B. H.; Dalton, L. R.. Journal of Materials Chemistry C. 2016, 4, 3119-3124. Doi: https://doi.org/10.1039/C6TC00358C
Published Date: June 7, 2018
Ultra-high electro-optic activity demonstrated in a silicon-organic hybrid modulator
Abstract: Efficient electro-optic (EO) modulators crucially rely on advanced materials that exhibit strong electro-optic activity and that can be integrated into high-speed and efficient phase shifter structures. In this paper, we demonstrate ultra-high in-device EO figures of merit of up to n3r33=2300 pm/V achieved in a silicon-organic hybrid (SOH) Mach–Zehnder modulator (MZM) using the EO chromophore JRD1. This is the highest material-related in-device EO figure of merit hitherto achieved in a high-speed modulator at any operating wavelength. The π-voltage of the 1.5-mm-long device amounts to 210 mV, leading to a voltage-length product of UπL=320 Vμm—the lowest value reported for MZM that are based on low-loss dielectric waveguides. The viability of the devices is demonstrated by generating high-quality on-off-keying signals at 40 Gbit/s with Q factors in excess of 8 at a drive voltage as low as 140 mVpp. We expect that efficient high-speed EO modulators will not only have a major impact in the field of optical communications, but will also open new avenues towards ultrafast photonic-electronic signal processing.
- Kieninger, C.; Kutuvantavida, Y.; Wolf, S.; Zwichel, H.; Blaicher, M.; Kemal, J.; Elder, D. L.; Lauermann, M.; Dalton, L. R.; Freude, W.; Randel, S.; Koos, C.. Optica. 2018, 5 (6) , 739-748. Doi: https://doi.org/10.1364/OPTICA.5.000739