2024

Bryant, Katherine; Hokkanen, Ari; Shahwar, Dura; Harjanne, Mikko; Salmi, Antti; Aalto, Timo

In this study, effective index birefringence and group index birefringence are investigated for 3 µm-thick silicon-on-insulator (SOI) strip waveguides, and experimental results are compared with simulations. We confirm zero group index birefringence at 1550 nm for a waveguide width of 2.6 µm; the absolute value of the same waveguide's group index birefringence is less than 2×10-4 over the measured 150 nm wavelength range. We further verify zero effective index birefringence at 1550 nm for a waveguide width of 3.2 µm, and the absolute value of its effective index birefringence is less than 6×10-5 over the same 150 nm wavelength range. Group and effective index birefringence dispersion are calculated based on the birefringence wavelength dependence, and the waveguide width needed to attain zero dispersion for either group or effective index birefringence is identified, at 3.1 µm and 2.7 µm, respectively. As a complement to our experimental findings, COMSOL simulations are conducted to analyze both the geometric- and stress-induced birefringence effects within the waveguides. The simulated birefringence values closely align with our experimental data, thereby validating the experimental results. We thus demonstrate the feasibility of achieving zero birefringence and zero birefringence dispersion through tuning the waveguide width in 3 µm SOI strip waveguides and validate these results via the agreement of a range of measurement methods and simulation.