Stress-Induced Birefringence Characteristics of Polymer Optical Rib Waveguides

We report the detailed numerical investigation of stress-induced material birefringence in polymer rib waveguide for the design of nonbirefringent waveguide devices. To accurately simulate the stress-induced effects we propose a more realistic model in the finite element analysis which considers the stresses induced over the entire sequential fabrication process. It is observed that the birefringence is nonuniform, and it is different for different etch depth and core width. The maximum birefringence in the core layer is observed near the lower cladding which decreases to zero toward the top surface. The influence of this material anisotropy on the modal birefringence is analyzed also for different rib structures. We found the stress effects on the modal birefringence to be largely affected by etch depth, while core width has small effect. It is also found that the deeply etched core has better birefringence stability. Finally, an accurate design of the zero-birefringence waveguide is illustrated by taking the stress effects into account, and the results are compared with experimental data. Excellent agreement between calculated and experimental results confirms the potential application of this work to aid in the design of polarization-insensitive waveguide devices.