Polyimide waveguiding at 830 nm

Abstract

In recent years several papers have investigated the optical properties of polyimides. However, most of the possible applications in the optoelectronic area would employ wavelengths in the near IR. To obtain an understanding of the factors which affect waveguide properties in this region lightguide experiments were conducted using a solid state laser with a wavelength of 830 nm. The main source of absorption of visible light in polyimides is the charge transfer complex (CTC) that is formed by overlap of the highest occupied molecular orbital of the diamine moiety with the lowest unoccupied molecular orbital of the five-membered imide ring. The behavior of the optical losses of a polyimide waveguide at 830nm can not be predicted from their behavior at 633nm. This is due to the fact that the CTC absorption does not affect the 830nm optical losses. In the near IR the waveguide quality of the investigated polyimides is solely due to molecular ordering up to the thermal decomposition temperature of the material. In most cases it is the thermal instability of the 6F that limits the useful processing range. To increase this range the 6F unit needs to be replaced by another, sterically and electronically similar acting group.