Photobleachable Donor-Acceptor-Donor Chromophores with Enhanced Thermal Stability

An important step in the realization of active optical interconnects is the development of poled electro-optic (EO) polymer materials stable to both manufacturing and end-use environments. These environments vary according to process and ultimate application, but many require longterm thermal stability to 125 °C and short excursions to 250 °C or higher.1 Our efforts with EO polymers have been directed toward thermally stable waveguide devices2 and polyimide-based guest-host material systems.3 We recently demonstrated a proof-of-principle all-polyimide triple stack Mach-Zehnder based on DCM (4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran) as the active chromophore in the core waveguide layer.4 The structure of DCM is shown in Figure 1(a). Advantages of DCM include low absorbance at device wavelengths, photobleachability, compatibility with polyimides and their polyamic acid precursors, and commercial ability at high purity. DCM is less than optimum in its thermal characteristics, however. It out-diffuses when heated above 220 °C for significant periods of time and it plasticizes the host material. This plasticization depresses the glass transition temperature Tg, and is detrimental to long-term stability of the poled state.