In this paper, we report on progress in the fabrication of a high speed optical phase modulator based on a nonlinear electro-optic (EO) polymer with an in-plane slotline radio frequency (RF) electrode structure. Compared to microstrip, a slotline RF electrode design has several potential advantages such as easy fabrication, high poling efficiency, low V(pi), and suppression of current drift. The guest-host nonlinear polymer system AJL49/APC was used in the device. Design, fabrication, and characterization are presented.