Volume relaxation in polymers and its effect on waveguide applications.

Abstract

Volume relaxation in polymers and the effect intrinsic to glassy polymers can significantly affect their refractive index over time. Its β rate has been found to be related only to relaxation temperature T and the glass transition temperature of the polymer T _g and not to the polymeric chemical structure. Universal values of β have been obtained for polymers and were used to predict the minimum index change related to volume in polymers. The index change is in the range from 7.86 × 10^-5 to 5.26 × 10^-4 when the T _g - T value of polymers is between 90 and 350 °C. These volume-relaxation-induced changes can cause serious deterioration or even failure in corresponding polymer waveguide devices, such as arrayed waveguide gratings and variable optical attenuators, when the T _g of a polymer is not sufficiently high. A minimum requirement is therefore suggested for the T _g of polymers used to fabricate waveguide devices.