## Photonics

#### different result for wavelength and frequency interplation TMM in FDTD

• xiaofei.xiao15
Subscriber

I am using TMM for a very simple simulaiton, however, When I use two different definition for wavelength (method 1) and frequency (method 2), the results are very different. Why?

thanks

closeall;
clear;

# method 1
lam0 = linspace(400e-9, 2000e-9,100); # frequency vector
f = c/lam0; # frequency vector, why this one is not correct?

# method 2
#f = linspace(c/400e-9, c/2000e-9,100); # frequency vector
#lam0 = c/f;

theta = 0; # angle vector
d = [0; 170e-6; 0]; # air/SiO2/Si/SiO2/air
nf = length(f);
nd = length(d);

# refractive index of each layer (dispersive)
n2 = matrix(nd,nf);
n2(1,1:nf) = 1; # air
n2(2,1:nf) = getfdtdindex("SiO2 (Glass) - Palik",f,min(f),max(f));
n2(3,1:nf) = 1; # air

RT2 = stackrt(n2,d,f,theta); # dispersive data index data, and theta from 0 to 45 deg

visualize(RT2);

plot(RT2.lambda*1e6,RT2.Rp,RT2.Rs,RT2.Tp,RT2.Ts,"wavelength (um)","Power","170um SiO2, theta=0");
legend("Rp","Rs","Tp","Ts");

R = RT2.Rp;
T = RT2.Tp;
matlabsave("170um_SiO2_R_T",lam0, R, T);

• xiaofei.xiao15
Subscriber

this seems the high-frequency FP cavity interference because of the SiO2 slab. Can we eliminate these fringes? because in the experiment, we would not see them .

thanks