Factors affecting polyimide lightguide quality

Lightguides were fabricated from three polyimides which contain one or two hexafluoroisopropylidene (6F) groups per repeat unit. As the number of 6F groups increases the optical losses of the corresponding lightguides decrease. Two mechanisms - ordering with or without charge transfer complex formation and voids or pinholes - are seen to be responsible for optical losses. The second type of losses can be reduced by cure optimization. Where ordering is possible annealing leads to increased optical losses. Geometrical restraint of the ordering, however, leads to loss reduction under otherwise identical conditions.