Marcatili’s extended approach: comparison to semi-vectorial methods applied to pedestal waveguide design

This paper deals with a theoretical study of pedestal waveguides. An extension of the Marcatili method has been developed in order to adapt this analytical method to pedestal structures. Simulations are performed for two different T-pedestal waveguide (T-PW) configurations corresponding respectively to a high and a lower core to pedestal widths ratio (T-PW I and T-PW II). Each configuration is simulated considering two core widths (2 and 4 mu m) and a core height ranging from 1 to 2 mu m at a 670 nm wavelength. Then, this extended Marcatili method has been compared with a semi-vectorial finite difference method (SVFD) and a spectral method developed by Galerkin, both based on a numerical approach. The simulation of the T-PW structure with these three methods shows a good congruence since the relative differences between Marcatili's method and the numerical methods remain below 6%. Then, the three approaches are applied to study the modal birefringence minimization in the case of pedestal structures. Simulations are typically performed for waveguide height and width values ranging, respectively, around (1.6-2.6) mu m and (1.8-6) mu m, with pedestal widths ranging around (0.4-0.8) mu m, at a 670 nm wavelength. The authors stress a specific property of pedestal configurations: by judiciously adjusting the dimensional parameters (core and pedestal width and core height), the birefringence can be completely screened out.