Hybrid sol-gel/polymer electro-optic modulators with horizontal taper structure have been designed and
fabricated. Optical transition between sol-gel passive waveguides and electro-optic polymer waveguides via horizontal
tapers has been realized in the electro-optic modulators. With 1cm interaction length these hybrid electro-optic
modulators have been measured to have a half-wave voltage of 8.91 V (dual drive 4.45 V), an extinction ration of
21.2dB and an optical insertion loss of 11.8 dB.
Host polymers play an important role in determining the thermal, optical and electrical properties of guest-host electro-optic (EO) polymers. In this study, a series of novel polymers, polyaryletherketones (PEKs) and polyarylethersulfones (PES'), were synthesized. After an initial screening on EO modulator fabrication-related properties, a PEK, LP120, was identified as a good candidate to host the highly stable chromophores (DH6 and DH52) developed in the company. Further optimization indicated that solvents in chromophore/polymer solutions have a strong impact on the quality of spin-coated films. DH6/LP120 and DH52/LP120 films spun from cyclopentanone gave lower optical losses of 1.97 and 1.55 dB/cm, respectively, when compared with 2.84 dB/cm for DH6/APC and 1.96 dB/cm for DH52/APC. Moreover, poling efficiencies as being reflected by EO coefficient were also improved by using LP120 compared to APC.
Polymeric electro-optical modulators have the advantages in bandwidth, driving voltage, and cost over lithium niobate
modulator for potential industrial, military and space applications. There are strict requirements on electro-optical
polymer materials to be used for practical device fabrication: large EO response, high thermal and photochemical
stability, low optical loss, high long-term stability and good processibility. Lots of progress in material design,
modification and optimization has been made based on theoretical calculation and actual material processing. However it
is very challenging to put all good properties into one material. We report the development of a chromophore series
based on 3,4-ethylenedioxythiophene structure and two host polymers based on 4,4'-(3,3,5-trimethylcyclohexylidene)
diphenol monomer. EO activity and optical loss at different chromophore loadings were systematically studied and
compared on various guest/host combinations. Specifically, DH-52/APC system was compared with DH-6/APC system,
showing improved overall electrical and optical properties. LP-116, with higher glass transition temperature than that of
APC, exhibits excellent mechanical property and compatibility with various chromophore guests. Especially, DH-67/LP-
116 has optical loss of 0.87 dB/cm. This indicates that LP-116 can substitute APC as an improved host polymer and DH-
52/LP-116 is highly feasible for the fabrication of EO devices with enhanced performance.
A series of 2-dimensional two-photon absorbing chromophores and their 1-dimensional analogs were studied. The influence of the solvents on the linear absorption, photoluminescence and two-photon absorption cross-sections were also examined for these chromophores. The stoke's shift increase with increasing solvent polarity, that can be adequately described by Lippert equation. Two-photon absorption cross sections were measured with femtosecond pulses by the two-photon-induced fluorescence technique. It was observed that two-photon cross-sections were also strongly dependent on the solvents, however no simple correlation with solvent polarity was found in this study. Interestingly, a linear relationship was observed in these chromophores between the molar extinction coefficient and the two-photon cross section when plotted in log-log formats. Understanding of the relationship may provide a better insight of the two-photon absorption processes, and potentially will contribute to the design of highly efficient two-photon absorbing chromophores.
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