Some of the most highly active organic electro-optic (EO) materials developed recently rely on the combination of an EO-active (chromophore-containing) host material (dendrimer or side-chain polymer) and an EO-active (chromophore) guest. These new binary-chromophore materials exhibit EO coefficients (r33) in the range of 250 to greater than 300 pm/V (currently as high as 450 pm/V). The EO activity of these binary-chromophore materials is greater the sum of their individual components. The experimentally observed increase in the nonlinear optical response of two representative classes of EO chromophore−EO dendrimer and EO chromophore−EO polymer mixtures relative to the response of the isolated components is described quantitatively herein by a physical model that accounts for cooperativity in the guest−host interactions.

This review provides a survey of nonlinear optical (NLO) chromophores and materials incorporating them which have been demonstrated over the last several years. Conventional polymeric materials, dendrimers, and other material design approaches are reviewed. Macroscopic nonlinear optical properties are introduced mainly in terms of second-harmonic generation (SHG) and the electro-optic (EO) effect. The temporal and thermal stability of nonlinear optical properties are also discussed. The review begins with a brief introduction explaining overall principles relating to the origin of second-order nonlinear optical properties. The structure of NLO materials, methods for their characterization, and structure–property relationships are also introduced. Much current research is aimed at optimizing microscopic nonlinearity in well-defined heterocyclic NLO chromophores which are then embedded in materials such as polymers, dendrimers, etc. Strong electron density donor and acceptor groups are connected through an efficient π-electron conjugative bridge to yield a highly electronically asymmetric and hyperpolarizable NLO chromophore. This review highlights the design and synthesis of recent chromophores that simultaneously exhibit large molecular hyperpolarizability, and low optical absorption at an operating wavelength, in addition to good processability and thermal/photochemical stability. Although NLO chromophores have been designed to exploit both dipolar and octupolar symmetry, the former has exhibited the strongest potential for the development of practical NLO devices. Organic materials based on polymers and dendrimers containing dipolar chromophores are mainly demonstrated for nonlinear optics. Experimental results corresponding to such dipolar compounds are mainly considered in this review. In addition, new strategies to improve thermal stabilities are also discussed herein.

A novel, thermally curable, tri-component organic glass for electro-optic applications was designed and synthesized. The system employed the Diels–Alder cycloaddition reaction to effect efficient cross-linking. The first component was a dendrimer containing multiple electro-optic chromophore substituents surrounded by an outer periphery possessing diene functionality. The second was a furan-protected, bis-dienophile electro-optic chromophore, introduced in order to function as a nonlinear optically-active cross-linking agent. The initial glass-transition temperature of the material was tuned by the addition of the third component, an optically-inert, maleimide-based dienophile cross-linking agent. Tuning of this mixture allowed optimum poling temperature to coincide with optimum thermal conditions for promotion of the Diels–Alder cross-linking reaction. The electro-optic properties of the material were evaluated in real-time, using a reflection-based single-beam ellipsometry apparatus that was modified to perform in situ signal monitoring. The high electro-optic activity observed (r33 of 150 pm V−1), was thermally stable up to 130 °C (a 48 °C improvement over similar uncross-linked materials). After processing, materials were insoluble in acetone, retained 90% of their original r33 after 15 months at room temperature, and performed well in accelerated operational testing at 85 °C in air.

Extensive experimental and theoretical study suggests that interchromophore electrostatic interactions are among the most severe impediments to the induction and stability of large electro-optic coefficients in electric-field-poled organic materials. In this report, multichromophore-containing dendritic materials have been investigated as a means to minimize unwanted attenuation of nonlinear optical (electro-optic) activity at high chromophore loading. The dendritic molecular architectures employed were designed to provide optimized molecular scaffolding for electric-field-induced molecular reorientation. Design parameters were based upon past experimental results in conjunction with statistical and quantum mechanical modeling. The electro-optic behavior of these materials was evaluated through experimental and theoretical analysis. Experimental data collected from the dendrimer structures depict a reasonably linear relationship between chromophore number density (N) and electro-optic activity (r(33)) demonstrating a deviation from the dipolar frustration that typically limits r(33) in conventional chromophore/polymer composite materials. The observed linear dependence holds at higher chromophore densities than those that have been found to be practical in systems of organic NLO chromophores dispersed in polymer hosts. Theoretical analysis of these results using Monte Carlo modeling reproduces the experimentally observed trends confirming linear dependence of electro-optic activity on N in the dendrimer materials. These results provide new insight into the ordering behavior of EO dendrimers and demonstrate that the frequently observed asymptotic dependence of electro-optic activity on chromophore number density may be overcome through rational design.

Alternating polymers of a nonlinear optical chromophore and bulky spacers were synthesized. High chromophore loading and efficient site isolation were achieved with this approach. The effects of chromophore loading density and electric poling field on the electro-optical (EO) properties of the polymers were carefully compared with those of guest-host systems of the same chromophore. The alternating polymer can be poled to higher EO efficiency under a lower poling field than the optimized guest-host system, while the lambda(max) of the polymer film is about 40 nm shorter than that of the guest-host system.

The title compound, C28H26N4OS, is an efficient non-linear optical (NLO) material and features a transoid configuration in contrast to the results of quantum chemical calculations. Molecules associate into layers via C-H center dot center dot center dot N interactions.

The title compound, C 28 H 26 N 4 OS, is an efficient non-linear optical (NLO) material and features a transoid configuration in contrast to the results of quantum chemical calculations. Mol­ecules associate into layers via C—H⋯N inter­actions.

Theoretical guidance, provided by quantum and statistical mechanical calculations, has aided the recent realization of electro-optic coefficients of greater than 300 pm/V (at 1.3 microns wavelength). This articles attempts to provide physical insight into those recent results and to explore avenues for the further improvement of electro-optic activity by structural modification, including to values of 500 pm/V and beyond. While large electro-optic coefficients are a necessary condition for extensive practical application of organic electro-optic materials, they are not a sufficient condition. Adequate thermal and photochemical stability, modest to low optical loss, and processability are important additional requirements. This article also examines such properties and suggests routes to achieving improved auxiliary properties.

The motivation for use of organic electro-optic materials derives from (1) the inherently fast (sub-picosecond) response of π-electron systems in these materials to electrical perturbation making possible device applications with gigahertz and terahertz bandwidths, (2) the potential for exceptionally large (e.g., 1000 pm/V) electro-optic coefficients that would make possible devices operating with millivolt drive voltages, (3) light weight, which is a concern for satellite applications, and (4) versatile processability that permits rapid fabrication of a wide variety of devices including conformal and flexible devices, three dimensional active optical circuitry, hybrid organic/silicon photonic circuitry, and optical circuitry directly integrated with semiconductor VLSI electronics. The most significant concerns associated with the use of organic electro-optic materials relate to thermal and photochemical stability, although materials with glass transition temperatures on the order of 200°C have been demonstrated and photostability necessary for long term operation at telecommunication power levels has been realized. This communication focuses on explaining the theoretical paradigms that have permitted electro-optic coefficients greater than 300 pm/V (at telecommunication wavelengths) to be achieved and on explaining likely improvements in electro-optic activity that will be realized in the next 1-2 years. Systematic modifications of materials to improve thermal and photochemical stability are also discussed.

Quantum and statistical mechanical calculations have been used to guide the improvement of the macroscopic electro-optic activity of organic thin film materials to values greater than 300 pm/V at telecommunication wavelengths. Various quantum mechanical methods (Hartree-Fock, INDO, and density functional theory) have been benchmarked and shown to be reliable for estimating trends in molecular first hyperpolarizability, β, for simple variation of donor, bridge, and acceptor structures of charge-transfer (dipolar) chromophores. β values have been increased significantly over the past five years and quantum mechanical calculations suggest that they can be further significantly improved. Statistical mechanical calculations, including pseudo-atomistic Monte Carlo calculations, have guided the design of the super/supramolecular structures of chromophores so that they assemble, under the influence of electric field poling, into macroscopic lattices with high degrees of acentric order. Indeed, during the past year, chromophores doped into single- and multi-chromophore-containing dendrimer materials to form binary glasses have yielded thin films that exhibit electro-optic activities at telecommunication wavelengths of greater than 300 pm/V. Such materials may be viewed as intermediate between chromophore/polymer composites and crystalline organic chromophore materials. Theory suggests that further improvements of electro-optic activity are possible. Auxiliary properties of these materials, including optical loss, thermal and photochemical stability, and processability are discussed. Such organic electro-optic materials have been incorporated into silicon photonic circuitry for active wavelength division multiplexing, reconfigurable optical add/drop multiplexing, and high bandwidth optical rectification. A variety of all-organic devices, including stripline, cascaded prism, Fabry-Perot etalon, and ring microresonator devices, have been fabricated and evaluated.

This communication primarily deals with utilizing organic electro-optic (OEO) materials for the fabrication of active wavelength division multiplexing (WDM) transmitter/receiver systems and reconfigurable optical add/drop multiplexers (ROADMs), including the fabrication of hybrid OEO/silicon photonic devices. Fabrication is carried out by a variety of techniques including soft and nanoimprint lithography. The production of conformal and flexible ring microresonator devices is also discussed. The fabrication of passive devices is also briefly reviewed. Critical to the realization of improved performance for devices fabricated from OEO materials has been the improvement of electro-optic activity to values of 300 pm/V (or greater) at telecommunication wavelengths. This improvement in materials has been realized exploiting a theoretically-inspired (quantum and statistical mechanics) paradigm for the design of chromophores with dramatically improved molecular first hyperpolarizability and that exhibit intermolecular electrostatic interactions that promote self-assembly, under the influence of an electric poling field, into noncentrosymmetric macroscopic lattices. New design paradigms have also been developed for improving the glass transition of these materials, which is critical for thermal and photochemical stability and for optimizing processing protocols such as nanoimprint lithography. Ring microresonator devices discussed in this communication were initially fabricated using chromophore guest/polymer host materials characterized by electro-optic coefficients on the order of 50 pm/V (at telecommunication wavelengths). Voltage-controlled optical tuning of the pass band of these ring microresonators was experimental determined to lie in the range 1-10 GHz/V or all-organic and for OEO/silicon photonic devices. With new materials, values approaching 50 GHz/V should be possible. Values as high as 300 GHz/V may ultimately be achievable.