Trial Function
A trial function is the starting point for the mode solver. The choice of a trial function
determines which mode is found, and the speed of convergence, but it should not affect the
accuracy of the computed mode. Just like the refractive index profiles, the trial function
can be entered in one of three ways:
-
An arbitrary two-dimensional profile can be uploaded as ASCII numeric values.
This profile must be uploaded as three separate text files. The first file
defines the x-grid. It is simply a column of numbers.
Click here for an example of the grid file. Similarly, the second file defines the y-grid.
The third file contains the trial function profile that corresponds
to the grid points defined in the previous two files.
Click here for an example of the profile file.
The refractive index file must
be arranged like:
N(x=1,y=1) N(x=2,y=1) N(x=3,y=1)....
N(x=1,y=2) N(x=2,y=2) N(x=3,y=2)....
-
The trial function can be created using a set of built-in polugon function. Each polygon is a
two dimenssional shape. The field value inside the polygon is specified by the user, and
the field outside the polygon is zero. Multiple polygons can be entered, and
most geometries of interest can be constructed this way. Click here for a complete description.
- The distribution profile from another job can be transferred to this job.
When a field, refractive index or function
is plotted
from the other program, there should be an option at the bottom of the screen for copying that
distribution as the trial function for another program.
Regardless of the size of the polygons, only the
the right-half of x=0 will be considered, and the symmetry condition
(symmetric or anti-symmetric) will be used to reflect the structure on the left-half of x=0.
Unlike the definitions of refractive index, the default background value is 0.0 (not 1.0).
Therefore, the trial function cannot be left blank. A trial function of zero everywhere
will crash the program. At the very least, a 'b 1.0' polygon must be specified.