The overlap and power coupling calculation can be used in applications such as the edge
coupler, where you are interested in knowing how much light is coupled from one waveguide
(here a fibre) to another.
The overlap, defined as the fraction of electro-magnetic fields that overlap between 2 field profiles,
is calculated using this formula, where E1, H1 are the fields from Mode 1, and E2, H2,
the fields from Mode 2.
The power coupling represents the fraction of power that couples from one mode to another.
If we consider the input mode (of power Pin) and the ith mode (of power Pi), the power
coupling is given by this formula.
Note the power coupling is a more practical value as it gives the fraction of power from
mode 1 that will actually propagate in mode 2 in the forward direction.
The calculation takes into account the reflected fields by assuming the reflected mode has
the same profile as the incoming field.
The “Overlap analysis” tool will calculate the overlap and the power coupling between
the selected mode and the selected field profile from the deck.
It is possible to shift the relative position of the modes and get, for instance, a plot
of the overlap vs the shift.
Note these features can be access from the user interface and from script commands.