A Polarisation Convertor
========================

This example uses a co-directional coupler arrangement to periodically
convert part of the zero order TE input mode to the zero-order TM mode.

The device is similar to that published in:

van der Tol, J. J. G. M., F. Hakimzadeh, et al. (1995).
"A new short and low-loss passive polarization convertor on InP." Phot. Tech. Lett vol. 7, pp. 32-34.


The simulation approximates the tilted side wall of the published device using a staircase of 4
slices.	Note that optimum performance is achieved if a little lateral offset is included between each
half period - see the join settings in the polnConvPer component. The FIMMPROP Scanner tool was used to determine this optimum.

Upon viewing the scattering matrix of polnConv, you will see that 80 percent of the zero order TE mode is converted into the zero order TM mode. You can observe this conversion by seperately plotting the Ex and Ey fields (view field profile/ plotted field)


Note also we use the "Periodic Section" rather than the "Simple Periodic Section". In the former, you can define the joint between each period. We use this joint to define the offset. 

We could alternatively have used zero-offset joins and altered the first and last slice widths of polnconv2a.rwg and polnconv2b.rwg to get the same effect, but changing the waveguide dimensions means that we have to re-compute the modes - much slower than scanning a join offset.


