Actually, not the cavity. There is an actual fiber there but it's hard to see a bit I think 😅 source is outside of the structure, it's located at x:-600nm , y: 0nm, z: 600nm. It's a plane wave source. Fiber is at the origin of simulation which is x:0, y:0 and z:0.  Whole simulation area geometry is xspan: 2000nm, yspan: 2000nm and zspan: 2000nm.

I used the script you mentioned and attached the integration result to "last_result" variable. Then I visualized it. Here is what I get:

I'm using 21 steps for the frequency band. When tried to see actual 3D monitor results, it gave me 53 datas for each frequency step. Now I can monitorize just frequency responses for "z" axis. I think this makes sense.