## Photonics

#### 2D Far-field

TAGGED: , ,

• noumanzia
Subscriber

Hello,

I am using this script to extract 2D far-field. Now I want to get the FF for a specific wavelength, lets say 1.5 µm. How can I do that using the second index of this function which is now "1"?

farfield2d("monitor",1);

• Guilin Sun
Ansys Employee

https://optics.ansys.com/hc/en-us/articles/360034410074-farfield2d-Script-command

• noumanzia
Subscriber

Hi  @Gullin Sun, I am aware of the link you shared but I do not know how to select a particular wavelength. The second parameter in the farfield2d function (the link you shared) is the frequency index but how this indexing works and how can I select a specific wavelength is still unknown. Lets say how can you select FF 1.55 µm wavelength or 200 THz?

• Guilin Sun
Ansys Employee

As you can see:

out = farfield2d("mname", f, n, illumination, periods, index, direction);

the value of "f" here is the frequency index; you can get the result at frequency number 5 like this:

efar5=farfield2d("monitor",5);

You cannot directly specify wavelength or frequency, but the frequency point only.

• noumanzia
Subscriber

How may I know which index points to which frequency and how are the indexes defined?

• noumanzia
Subscriber

There is a huge difference in the FF results when index 1 or 100 is selected.

• Guilin Sun
Ansys Employee

This is correct, since the frequency is very different from point 1 to point 100.

You can extract the frequency, eg:

f=getdata("monitor","f");

then you can calculate wavelength. Please note that f(1) is the smallest corresponding to longest wavelength.

You may need to watch some online 100-level courses:

https://optics.ansys.com/hc/en-us/sections/360007813194-FDTD100-List-of-videos