Poly(methyl methacrylate-co-9-anthrylmethyl methacrylate) (PMMA-AMA) LP-136 with various AMA contents was
prepared. The polymer was modified via Diels-Alder (D-A) type "click chemistry". In one approach, the side-chain was
grafted stepwise with maleimide-containing chromophore AJL-04 followed with N-phenylmaleimide (PI) to form LP-160. LP-160 was doped with 30 wt % of chromophore AJLS-102 to give electro-optic (EO) core polymer AJ-415. In the
other approach, all the pending AMA groups were modified with PI in one step to yield LP-165. Doping 33.7 wt %
AJLS-102 in LP-165 gives another core polymer AJ-416. The EO and material properties of both polymers were
systematically studied. Via careful selection of bottom and top cladding materials with proper optical and electrical
properties, Mach-Zehnder type modulators were fabricated based on both core materials. At the operational wavelength
of 1550 nm, modulator with AJ-415 core has half-wave driving voltage (Vπ) of 0.95 V and insertion loss of 19.1 dB,
while the best results from modulators with AJ-416 core are 0.75 V of Vπ and 17.1 dB of insertion loss. AJ-416 also has
the advantage over AJ-415 for building EO modulator with better processibility and long-term stability.
A major breakthrough in the area of organic electro-optic (EO) materials has been recently achieved. To go beyond the
oriented gas model limit for organic EO materials, new approaches of using nanoscale architecture control and
supramolecular self-assembly have been proved as a very effective method to create a new paradigm for materials with
very exciting properties. High-performance EO polymers were demonstrated by a facile and reliable Diels-Alder "click"
reaction for postfunctionalization and lattice hardening to improve EO activity and thermal stability. This type of "click"
chemistry paves the way to systematically study the relationship among EO activity, chromophore shape, and number
density of the chromophores. Reversible supramolecular interactions were also introduced to a new generation of EO
dendrimers and polymers to create self-assembled nano-objects, overcome strong intermolecular electrostatic
interaction, and improve their poling efficiency and stability. These self-organized EO materials were used as hosts in a
binary chromophore system to further improve chromophore number density and r33 value. With these novel approaches,
we succeeded in enlarging the full potential of organic NLO materials by a factor of 3~5 and developing a variety of
nano-structured organic EO materials with ultrahigh r33 values (>300 pm/V at the wavelengths of 1310 and 1550 nm,
more than 10 times that of LiNbO3) and excellent auxiliary property, such as thermal stability and optical transparency.
The success of these material developments has inspired the exploration of new device concepts to take full advantage of
organic EO materials with ultrahigh r33 values.
A series of side-chain electrooptic (E-O) polymers have been prepared by Diels-Alder reaction in a solid state and characterized for their nonlinear optical properties. A synthesized chromophore were easily attached to a pendent anthracenyl moiety functionalized on the poly(methylmethacrylate-co-anthrylmethylmethacrylate) thermally in the bulk films during the poling process without compromising E-O performances. We have also controlled a chromophore concentration to determine its critical loading density at which chromophore-chromophore electrostatic interaction occurs in the polymer matrix. The highest E-O coefficient was 110 pm/V for the 34 wt% of the doped chromophore in the polymer at the wavelength of 1.3 μm. A high loading density of chromophore was obtained without observing a severe phase separation in the polymer matrix by an AFM morphology study. This novel approach provides to demonstrate a strategy for developing highly efficient E-O materials with the full potential of a chromophore.
Recent breakthroughs in developing exceptional organic electro-optic (EO) materials are reviewed. Whole series of guest-host polymers furnished with high μβ chromophores have shown large electro-optic coefficients around 100~160 pm/V @ 1.31μm. Moreover, new generation of NLO chromophores based on pyrroline and pyrrolizine acceptors have been designed and synthesized. To go beyond the typical oriented gas model limit for poled polymers, new approach of
using nanoscale architecture control and supramoleaular self-assembly has been proved as a very effective method to create a new paradigm for materials with very exciting properties. The approaches of employing Diels-Alder reactions for postfunctionalization and lattice hardening also provide a facile and reliable way to generate high-performance EO polymers and dendrimers. This type of "click" chemistry paves the way to systematically study the relationships between chromophore shape and number density, controlled self-assembly, in addition to provide the material properties needed for multi-layer device fabrication. Finally, a new generation of binary monolithic glasses has been developed that exhibit unprecedented high EO activities through careful manipulation of intricate supramolecular interactive forces for self-assembly. The results obtained from these poled binary organic glass materials (r33 as high as 310 pm/V at 1.31μm) are the highest values ever reported which are >10 times of the commercial lithium niobate crystals. The success of these material developments has recently inspired the exploration of new device concepts trying to take full advantage of the organic EO materials with ultrahigh r33 values.
Using modified Teng-Man reflection ellipsometry, very high linear electro-optic coefficients (r33 = 250 - 300 pm/V) have been measured in thin films of poled organic glasses. The glasses consist of two chromophores designed to yield synergistically enhanced orientation during the poling process. The chromophores were ordered by the contact poling method under moderate electric fields of ~ 0.44 MV/cm. Compared to measurements made 1-4 hours after poling, the electro-optic coefficient relaxed to a value about 15% lower in a period of one week and thereafter remained relatively stable at room temperature. We report both standard Teng-Man reflection type measurements made at a 45° angle of incidence as well as a more complete analysis of nonlinear reflection ellipsometric data as a function of angle of incidence and optical bias. The more complete analysis takes into account the properties of the multilayer stack structure of the test samples consisting of glass/ITO/NLO-organic/gold. Limitations of a simple model to analyze Teng-Man reflection data will be discussed, as well as contributions of electrochromism.
Jingdong Luo, Sen Liu, Marnie Haller, Jae-Wook Kang, Tae-Dong Kim, Sei-Hum Jang, Baoquan Chen, Neil Tucker, Hongxiang Li, Hong-Zhi Tang, Larry Dalton, Yi Liao, Bruce Robinson, Alex Jen
Recent development of high-performance nonlinear optical polymers for electro-optics (E-O) is reviewed in this paper. A highly efficient and thermally stable nonlinear optical (NLO) chromophore, namely 2-[4-(2-{5-[2-(4-{Bis-(tert-butyl-dimethyl-silanyloxy)-ethyl]-amino}-phenyl)-vinyl]-thiophen-2-yl}-vinyl)-3-cyano-5-trifluoromethyl-5H-furan-2-ylidene]-malononitrile, has been prepared and incorporated in amorphous polycarbonate (APC) composites. The result from high electric field poling shows a very large E-O coefficient (r33 = 94 pm/V at 1.3 μm), ~80% of which can be maintained at 85 °C for more than 500 hours. In addition to this guest/host sysytem, a high Tg side-chain polymer, derived from a 3-D cardo-type polimide with dendron-encapsulated chromophores as pendent groups has also been synthesized and characterized. A high degree of chromophore dipole orientation and a large r33 of 71 pm/V at 1.3 μm can be achieved in this poled polyimide. More than 90% of its E-O activity can be maintained at 85 °C for more than 600 hours. To access the full potential of poled polymers for device applications, we have developed a new lattice-hardening approach to overcome the “nonlinearity-stability-tradeoff” of conventional thermoset methods. By using the Diels-Alder lattice-hardening process, we can achieve the same high poling efficiency and large r33value as in a guest-host system while maintaining good thermal stability seen in densely-crosslinked polymers. By modifying the electronic properties of the crosslinking reagents, we can fine-tune the processing temperature window of the Diels-Alder reactions to achieve hardened materials with optimal properties.
Recent progress in developing high-performance organic polymers for electro-optics and photonics is reviewed. A highly fluorinated hyperbranched aromatic polymer with the degree of branching around 0.51 was prepared by a mild one-step polyesterification of an AB2 type monomer. Further post-functionalization with and thermally cross-linking by aromatic trifluorovinyl ethers (TFVE) afforded thermally stable, low loss optical polymer with improved solvent resistance. By more precisely controlling the molecular nano-architecture, we have developed a series of highly fluorinated crosslinkable dendrimers. These materials possess most of the desirable properties needed for the fabrication of optical waveguides, such as high solubility in common organic solvents (up to 50 wt%), very low optical loss, and excellent thermal stability. To overcome the “nonlinearity-stability tradeoff,” a facile and reversibly crosslinkable NLO polymer system is developed that combines both advantages of high poling efficiency and good alignment thermal stability. By smartly controlling the poling and crosslinking processes through the reversible Diels-Alder (DA) reactions, it allows highly polarizable chromophores to be efficiently poled at the stage of low viscosity linear thermoplastic polymer. The resulting nonlinear optical polymer exhibits a combination of a very large r33 value (76 pm/V at 1.3 μm) and good temporal stability at 70°C.
Recent progress in developing high-performance nonlinear optical chromophores and polymers for electro-optics is reviewed. Using the single-mode focused microwave irradiation, a diversified family of 2,5-dihydrofuran derivatives has been synthesized as a new class of tunable electron acceptors. Very large r33 values (128 and 116 pm/V at 1.3 μm) have been demonstrated by doping one of the 2-dicyanomethylen-3-cyano-4,5,-dimethyl-5-trifluoromethyl-2,5-dihydrofuran (CF3-TCF)-based chromophores in poly(methyl methacrylate) (PMMA) and a high Tg polyquinoline (PQ-100), respectively. An excellent long-term temporal stability at 85°C has also been maintained in the PQ system. Two side-chain dendronized NLO polymers have been synthesized. Using a mild, simple, and generally applicable post-functionalization method, highly polarizable chromophores with dendritic modification has been covalently attached to side chains of poly(4-hydroxystryene). This approach provides the combined advantages of achieving better poling efficiency through the dendritic effect and shortening the development time required for E-O dendrimer synthesis. Systematic property comparison between these polymers and other conventional NLO polymers, such as guest-host and simple side-chain polymers, has been performed. Exceptionally high poling efficiency (a very large E-O coefficient of 97 pm/V at 1.3 μm) and good temporal stability at room temperature were dmeonstrated in this dendronized side-chain polymer system.
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