Thermo-optic coefficients of polymers for optical waveguide applications

Polymers with diverse chemical structure were evaluated to establish an empirical relationship between their thermo-optic coefficients (dn/dT) and coefficients of thermal expansion (α) according to the Lorentz–Lorenz equation. The results have showed that, regardless their chemical structure and Tgs, all the evaluated polymers follow a single linear relationship between their dn/dT values and α values with the slope (δn/δT)ρ equal to 0.56 and the interception (ρδn/δρ)T equal to −3.7×10−6. The relationship can be used to estimate the dn/dT value of a given polymer using its α value, which is widely available and can be easily measured using TMA and other conventional equipment, and the estimated dn/dT value is useful for developing polymers and evaluating device performance in optical waveguide applications.