Figure 2 : The effective refractive index of the TE and TM modes.

From: Polarisation independent silicon-on-insulator slot waveguides

Figure 2

The dashed lines denote TE modes while the solid lines denote TM modes. The points at which the corresponding solid and dashed lines cross are marked with various shapes, giving the value of wright at which there is no difference in the effective refractive index, that is, there is zero-birefringence. For both figures, the width of the left rail wleft is fixed at 150 nm while the width of the right rail wright is varied. The waveguides were taken to be straight and to have vertical walls. (a) Changing the size of the slot while the height is fixed at 220 nm and (b) changing the height while the slot is fixed at 140 nm. The corresponding effective refractive indices of the modes are calculated. We found that such behaviour is typical for all slot waveguides we studied which have one TE and one TM mode.