Simultaneous measurement of thermo-optic and stress-optic coefficients of polymer thin films using prism coupler technique.
We present a simple method for simultaneous measurement of thermo-optic and stress-optic coefficients of polymer thin films by measuring the film refractive indices as a function of temperature (dn/dT). Usually, such dn/dT value is considered as the thermo-optic coefficient. However, in the thin film systems, the measured dn/dT values result from both the thermo-optic and stress-optic effects. To demonstrate the stress-induced effects, the dn/dT values have been investigated for two different polymers: benzocyclobutene (high film stress) and epoxy 3505 (negligible film stress), using a prism coupler technique. The finite element method has been used so as to predict the stresses in the polymer film and, by combining them with the experimental dn/dT values, the individual thermo-optic and stress-optic coefficients have been determined. We found that the obtained thermo-optic coefficient is significantly different than the measured dn/dT values. The method is generic in nature and can thus be applied to a wide range of polymer waveguide materials.
Hossain
Md Faruque
MF
Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong, China.
Chan
Hau Ping
HP
Uddin
Mohammad Afsar
MA