To simulate a waveguide with an angle, first the waveguide will need to be rotated, like the screenshot below.
The Mode Source also need to be rotated to get the proper cross section to calculate the eigenmode for injection.
In some situation, the option “rotation offset” is also needed. This is to avoid taking other unwanted structures in the eigenmode calculation. In this grating coupler example, the “rotation offset” is on to make sure the si waveguide is out of the way when calculating the fiber modes. When there is a value in the “rotation offset” option, it will general a plane of reference and move to the offsetted location. In the screenshot below, the plane of reference appears out of the simulation region and the original source is still inside the simulation region. The source will be injected at the location where the source is specified at the geometry tab. Side note, the mode expansion monitor will behave in a very similar way.