Electro-optic polymers for high speed modulators

Different electro-optic polymer systems are analyzed with respect to their electro-optic activity, glass transition temperature (Tg) and photodefinable properties. The polymers tested are polysulfone (PS) and polycarbonate (PC). The electro-optic chromophore, tricyanovinylidenediphenylaminobenzene (TCVDPA),which was reported to have a highest photochemical stability [1] has been employed in the current work. Modified TCVDPA with bulky side groups has been synthesized, and a doubling of the electro-optic coefficient (r33) compared to the unmodified TCVDPA has been shown. The plasticizing effect of the chromophore, has been reduced by attaching it to the polymer backbone. SU8 (passive) and PC-TCVDPA (active) channel waveguides were fabricated by photodefinition technique and the passive waveguide losses were measured to be 5 dB/cm at 1550 nm. Over the past few years there has been an increased interest in electro-optic polymers for telecommunication applications. Due to their potential for low drive voltage, integration ability, low optical losses in the 1.3 and 1.55 μm telecommunication windows, and low dispersion of refractive index between optical frequencies and millimeter waves, electro-optic polymer modulators are being targeted for > 40 Gb/s data rate communication systems. Polymer electro-optic modulators operating at 1.3 μm with drive voltages < 1 V and modulation bandwidths ranging from 150-200 GHz have been demonstrated [2]. Practical integration of these devices to telecommunication systems depends not just on the modulation and bandwidth milestones, but also on short and long term performance requirements. Polymer electro-optic modulators typically consist of waveguides with polymer core material and cladding layers, designed to form either a Mach-Zehnder interferometer, or a microring resonator. In both cases the core material consists of electro-optic chromophores either doped into, or covalently attached to the host material. The chromophores are responsible for the electro-optic activity in the material. The specific chromophore used will determine the photochemical stability of the device. The host material plays a critical role in the overall design, fabrication methods, and thermal stability. The chromophore and the host material together determine the optical losses. The chromophore can be simply doped in the host (guest-host polymer), attached as side chain, or even crosslinked between different polymer backbones. To date several host materials like PMMA, polyimide, polyurethane etc., have been used for both material and device studies. In the current work we report the usage of the TCVDPA chromophore in two different host materials namely, polysulfone and polycarbonate (the high Tg version). Solutions of PS and PC were prepared in Proceedings Symposium IEEE/LEOS Benelux Chapter, 2005, Mons