Learning Forum

[ldepra]

Hello, I am currently trying to simulate a 40nm thin film of Au using FDTD with a plane wave incidence at 1550nm, 0BW. 

After analyzing my results I have noticed that my reflection and transmission values are not making sense. I am currently using Periodic boundaries along the directions of NON-propagation and PML boundaries along the direction of propagation. I also have listed the script below if anyone is interested in the setup.

 

selectall; deleteall; clear;

 

 

slab_x=20e-9;

slab_yz=100e-9;

 

#Setting up simulation region

addfdtd;

set("background index",1);

set("x min",-slab_x/2-5000e-9);

set("x max",slab_x/2+5000e-9);

set("y min",-slab_yz/2);

set("y max",slab_yz/2);

set("z min",-slab_yz/2);

set("z max",slab_yz/2);

set("x min bc","PML");

set("x max bc","PML");

set("y min bc","Periodic");

set("y max bc","Periodic");

set("z min bc","Periodic");

set("z max bc","Periodic");

#set("mesh type","uniform");

#set("dx",0.5e-9);

#set("dy",5e-9);

#set("dz",5e-9);

 

 

 

#Setting Up Plane Wave

addplane;

set("injection axis","x");

set("x",-slab_x/2-3000e-9);

set("y min",-slab_yz/2);

set("y max",slab_yz/2);

set("z min",-slab_yz/2);

set("z max",slab_yz/2);

set("center wavelength",1.55e-6);

set("wavelength span",0.0e-6);

 

 

#Setup Gold Material

addrect;

set("x min",-slab_x/2);

set("x max",slab_x/2);

set("y min",-slab_yz/2);

set("y max",slab_yz/2);

set("z min",-slab_yz/2);

set("z max",slab_yz/2);

set("material","Au (Gold) - Palik");

 

 

#Setting Up Monitors R

addpower;

set("Monitor Type","2D X-Normal");

set("x",-slab_x/2-4000e-9);

set("y min",-slab_yz/2);

set("y max",slab_yz/2);

set("z min",-slab_yz/2);

set("z max",slab_yz/2);

 

#Setting Up Monitors R

addpower;

set("Monitor Type","2D X-Normal");

set("x",slab_x/2+4000e-9);

set("y min",-slab_yz/2);

set("y max",slab_yz/2);

set("z min",-slab_yz/2);

set("z max",slab_yz/2);

 

 

#Adding Movie

addmovie;

set("x min",-slab_x/2-5000e-9);

set("x max",slab_x/2+5000e-9);

 

[Amrita Pati]

Hi Lucio,

If the source is injected in the +x/y/z direction, then the transmission will be positive and reflection will be negative by convention.

So, when you add up the transmission and reflection make sure you use T - R (where R will be negative by convention).

If it is along the -x/y/z directions, use -T + R (where T will be neagtive by convention).

 

That being said, I would still expect gold to have a finite amount of absorption at 1550 nm. So, I would expect the sum of transmission and reflection to be less than 1. I will recommend performing convergence testing to confirm the validity of the results, especially if you think they are unreasonable at the moment.

 

Regards,
Amrita