Characteristics of stress-birefringence in polymer optical strip waveguides with air cladding

Thermal stress which is unavoidably generated in the fabrication process alters the optical property of the waveguide materials and thus hinders the realization of polarization insensitive devices. This work reports the detailed numerical investigation of stress-induced birefringence in polymer strip waveguide. A more realistic model is used in the finite element analysis to estimate the stresses induced over the entire sequential fabrication process. It is observed that the birefringence in the strip channel is non-uniform which is maximum near the lower cladding and decreases to zero towards the top of the channel. The variation in birefringence is also influenced by the waveguide geometries. Such birefringence characteristics are obtained and discussed in a generalized form, allowing for their applicability with various polymer materials. Thus, the generalized characteristics can be used to determine the stress-birefringence of a polymer strip waveguide with air cladding only by knowing the stress-birefringence in its planar film. This will eliminate the necessity of extensive numerical analysis for the prediction of thermal stress in polymer waveguides and will be more accurate than analytical solutions.