Reply To: Sign convention of diffraction order numbers of Lumerical FDTD/RCWA ?

[Guilin Sun]

You are right that people use different conventions. Caution should be taken when to interpret the result.

In Lumerical products, we usually follow the theta, phi convention:

https://optics.ansys.com/hc/en-us/articles/360034394294-Understanding-direction-unit-vector-coordinates-in-far-field-projections

A little more:

usually theta is actually from 0 to 90deg, as it uses the monitor normal as reference. So when light is propagating along +z, the reflection theta angles will be positive as we use cosine (from squareroot operation) to get the angle in degree.