Cross-polarization generation and its impact on coupler performance

In high index contrast integrated optic waveguides, it has been found that waveguide asymmetries can produce cross-polarization coupling. This effect has been well studied for polarization rotation. A similar effect, as produced by fabrication-induced asymmetry, can significantly limit the performance of directional couplers. In this paper, we analyze the effect, propose a method to circumvent these manufacturing-related limitations, and demonstrate an improvement of the extinction ratio from 25 to 40 dB level