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1. Birefringence, dimensionality, and surface influences on organic hybrid electro-optic performance

   https://doi.org/10.1117/12.2594939  

   Johnson, Lewis E. ; Elder, Delwin L. ; Benight, Stephanie J. ; Tillack, Andreas F. ; Hammond, Scott R. ; Heni, Wolfgang ; Dalton, Larry R. ; Robinson, Bruce H. ( August 2021 , Physical Chemistry of Semiconductor Materials and Interfaces XX)

   Congreve, Daniel ; Nielsen, Christian ; Musser, Andrew J. ; Baran, Derya (Ed.)

   Hybrid organic electro-optic (OEO) devices consist of a layer of ordered organic chromophores confined between layers of metals or semiconductors, enabling optical fields to be tightly confined within the OEO material. The combination of tight confinement with the high electro-optic (EO) performance of state-of-the art OEO materials enables exceptional electro-optic switching performance in silicon-organic hybrid (SOH) and plasmonic-organic hybrid (POH) device architectures. Recent records in POH devices include bandwidths > 500 GHz and energy efficiency < 100 aJ/bit. However, optimization of device performance requires both understanding and improving the degree to which chromophores can be acentrically ordered near a metal or semiconductor interface. Applying bulk and/or isotropic models of OEO materials to nanophotonic device architectures often lead to overly optimistic translation of materials performance to device performance. Prior work has identified influences of high centrosymmetric order (birefringence), altered relations between acentric and centrosymmetric order (dimensionality), and surface electrostatics on chromophore ordering. We combine these models into a representation that can be used to understand the influences of these phenomena on device performance, how some prior OEO materials exhibited unusually high performance under confinement, how ordering close to surfaces may be improved, and implications for future electro-optic device design. 

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2. Electro‐Optic Activity in Excess of 1000 pm V −1 Achieved via Theory‐Guided Organic Chromophore Design

   https://doi.org/10.1002/adma.202104174  

   Xu, Huajun ; Elder, Delwin L. ; Johnson, Lewis E. ; de Coene, Yovan ; Hammond, Scott R. ; Vander Ghinst, Wouter ; Clays, Koen ; Dalton, Larry R. ; Robinson, Bruce H. ( September 2021 , Advanced Materials)

   High performance organic electro‐optic (OEO) materials enable ultrahigh bandwidth, small footprint, and extremely low drive voltage in silicon‐organic hybrid and plasmonic‐organic hybrid photonic devices. However, practical OEO materials under device‐relevant conditions are generally limited to performance of≈300 pm V⁻¹(10× the EO response of lithium niobate). By means of theory‐guided design, a new series of OEO chromophores is demonstrated, based on strong bis(4‐dialkylaminophenyl)phenylamino electron donating groups, capable of EO coefficients (r₃₃) in excess of 1000 pm V⁻¹. Density functional theory modeling and hyper‐Rayleigh scattering measurements are performed and confirm the large improvement in hyperpolarizability due to the stronger donor. The EO performance of the exemplar chromophore in the series, BAY1, is evaluated neat and at various concentrations in polymer host and shows a nearly linear increase inr₃₃and poling efficiency (r₃₃/E_p, E_pis poling field) with increasing chromophore concentration. 25 wt% BAY1/polymer composite shows a higher poling efficiency (3.9 ±0.1 nm²V⁻²) than state‐of‐the‐art neat chromophores. Using a high‐ε charge blocking layer with BAY1, a record‐highr₃₃(1100 ±100 pm V⁻¹) and poling efficiency (17.8 ±0.8 nm²V⁻²) at 1310 nm are achieved. This is the first reported OEO material with electro‐optic response larger than thin‐film barium titanate.

    

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3. Bis(4-dialkylaminophenyl)heteroarylamino donor chromophores exhibiting exceptional hyperpolarizabilities

   https://doi.org/10.1039/d0tc05700b  

   Xu, Huajun ; Johnson, Lewis E. ; de Coene, Yovan ; Elder, Delwin L. ; Hammond, Scott. R. ; Clays, Koen ; Dalton, Larry R. ; Robinson, Bruce H. ( March 2021 , Journal of Materials Chemistry C)

   Organic electro-optic (EO) materials incorporated into silicon-organic hybrid and plasmonic-organic hybrid devices have enabled new records in EO modulation performance. We report a new series of nonlinear optical chromophores engineered by theory-guided design, utilizing bis(4-dialkylaminophenyl)heteroarylamino donor moieties to greatly enhance molecular hyperpolarizabilities. Hyperpolarizabilities predicted using density functional theory were validated by hyper-Rayleigh scattering measurements, showing strong prediction/experiment agreement and >2-fold advancement in static hyperpolarizability over the best prior chromophores. Electric field poled thin films of these chromophores showed significantly enhanced EO coefficients ( r 33 ) and poling efficiencies ( r 33 / E p ) at low chromophore concentrations compared with state-of-the-art chromophores such as JRD1 . The highest performing blend, containing just 10 wt% of the novel chromophore BTP7 , showed a 12-fold enhancement in poling efficiency per unit concentration vs. JRD1 . Our results suggest that further improvement in chromophore hyperpolarizability is feasible without unacceptable tradeoffs with optical loss or stability. 

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4. New paradigms in materials and devices for hybrid electro-optics and optical rectification

   https://doi.org/10.1117/12.2595638  

   Johnson, Lewis E. ; Elder, Delwin L. ; Xu, Huajun ; Hammond, Scott W. ; Benight, Stephanie J. ; O'Malley, Kevin ; Robinson, Bruce H. ; Dalton, Larry R. ( August 2021 , Molecular and Nano Machines IV)

   Sekkat, Zouheir ; Omatsu, Takashige (Ed.)

   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. 

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5. Integrated lithium niobate electro-optic modulators: when performance meets scalability

   https://doi.org/10.1364/OPTICA.415762  

   Zhang, Mian ; Wang, Cheng ; Kharel, Prashanta ; Zhu, Di ; Lončar, Marko ( May 2021 , Optica)

   Electro-optic modulators (EOMs) convert signals from the electrical to the optical domain. They are at the heart of optical communication, microwave signal processing, sensing, and quantum technologies. Next-generation EOMs require high-density integration, low cost, and high performance simultaneously, which are difficult to achieve with established integrated photonics platforms. Thin-film lithium niobate (LN) has recently emerged as a strong contender owing to its high intrinsic electro-optic (EO) efficiency, industry-proven performance, robustness, and, importantly, the rapid development of scalable fabrication techniques. The thin-film LN platform inherits nearly all the material advantages from the legacy bulk LN devices and amplifies them with a smaller footprint, wider bandwidths, and lower power consumption. Since the first adoption of commercial thin-film LN wafers only a few years ago, the overall performance of thin-film LN modulators is already comparable with, if not exceeding, the performance of the best alternatives based on mature platforms such as silicon and indium phosphide, which have benefited from many decades of research and development. In this mini-review, we explain the principles and technical advances that have enabled state-of-the-art LN modulator demonstrations. We discuss several approaches, their advantages and challenges. We also outline the paths to follow if LN modulators are to improve further, and we provide a perspective on what we believe their performance could become in the future. Finally, as the integrated LN modulator is a key subcomponent of more complex photonic functionalities, we look forward to exciting opportunities for larger-scale LN EO circuits beyond single components.

    

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