Buried channel wave guides have been fabricated from thermally stable non linear optical polyimides. The Material system consists of a polyimide cladding and a polyimide based active Material. The buried channel wave guides are fabricated by a trench and fill process. This process was used for the fabrication of active wave guides at process temperatures above 300 °C. Single Mode wave guides, and Mach-Zenhder interferometers, were fabricated with attenuation < 2 dB/cm. Active Mach-Zehnder interferometers with a Vπ phase shift of 50 volts and the low attenuation were fabricated. Thermal aging of the poled active device demonstrated no change in activity after 30 Minutes at 230°C.