Measurement of the thermo-optical effect of integrated waveguides

Abstract

Thermo-optical switches are widely used in integrated optics and various types of integrated optical structures have been reported in literature. These structures include, but are not limited to Mach-Zehnder-Interferometer (MZI) switches and digital optical switches. The thermo-optical effect depends on the refractive index, the polarizability and the density of a material. The polarizability effect can often be neglected and the change of refractive index is dominated by a density change due to the thermal expansion of the material. We report herein a new method to measure the thermo-optical effect of waveguides directly, using integrated MZIs fabricated in polymer waveguide technology. Common methods rely on macroscopic samples, but the properties can differ significantly for micro-structured waveguides. Using a floodlight halogen rod lamp and metal-shields, we realized a radiation heater with a trapezoidal-shaped heating pattern. While the heating occurred from the bottom side, a thermocouple was placed on top of the sample. By dynamically measuring the temperature and the corresponding output-power of the MZI, the temperature difference between constructive and destructive interference can be determined. Multiple measurements of different sample MZIs exhibit an average thermo-optical coefficient (TOC) of 1.6 ∗ 10-4 1/K .