Hossain Md Faruque, Chan Hau Ping, Uddin Mohammad Afsar
Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong, China.
Appl Opt. 2010 Jan 20;49(3):403-8. doi: 10.1364/AO.49.000403.
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.
我们提出了一种简单的方法，通过测量聚合物薄膜的折射率随温度的变化（dn/dT）来同时测量其热光系数和应力光系数。通常，这样的dn/dT值被视为热光系数。然而，在薄膜系统中，测得的dn/dT值是热光效应和应力光效应共同作用的结果。为了证明应力诱导效应，我们使用棱镜耦合器技术研究了两种不同聚合物的dn/dT值：苯并环丁烯（薄膜应力高）和环氧3505（薄膜应力可忽略不计）。采用有限元方法预测聚合物薄膜中的应力，并将其与实验测得的dn/dT值相结合，确定了各自的热光系数和应力光系数。我们发现，获得的热光系数与测得的dn/dT值有显著差异。该方法本质上具有通用性，因此可应用于广泛的聚合物波导材料。
