## Photonics

#### Magnetooptical materials , Polarisation Rotation

• sandeep_chamoli
Subscriber

Hi Team,

I am want to do the magnetooptical material simulation. I have a tensor of magnetooptical material from literature. I have few questions.

(1) the value we need to keep here in FDTD material data base is the eigen value of this tensor?

• Guilin Sun
Ansys Employee
A1: the values here are from the diagonalized elements: exx,eyy, ezz
A2: U is the conjugate transpose of the eigen vector V. If it is real matrix, then it is just a transpose.
Only when you know the material diagonal tensor can you use the rotation transformation. Permittivity rotation grid attribute
A3: propagation direction does not define the tensor, it is the tensor that defines the material anisotropy. Therefore, you may need to know what anisotropy of the material you desire to have light propagating along z. Please find more information about anisotropy and light polarization from some books.

• sandeep_chamoli
Subscriber
HI , Thanks.
I am able to see the rotation in the polarisation, this part is fine.
But i have a question.
first, i am going +z direction , and i have certain pol rotation in light after passing through the magnetooptical material. I can calculate that pol state using pol ellipse, as given here. https://support.lumerical.com/hc/en-us/articles/360034395234-Calculating-the-far-field-polarization-ellipse
Now, when i am going back (-z), why the polarisation is going back to its original state , i think it should further add polarisation ?
• Guilin Sun
Ansys Employee
Not sure what do you mean "the original state". Is it the same as the +z polarization state, or the incident state? The device is not special to separate forward and backward propagation. Please first test online example. As long as everything setting is the same as +z case, except the propagation direction, I do not see any physics that prevent to have the same result, except it is the kind of circulator. Please carefully check the settings and think over the physics.
• sandeep_chamoli
Subscriber
Hi, Noted.
Can you please tell me , how to get the information of apmplitude of S and P light from the following figure. Because once we know the S and P amplitudfe and their phase difference (which is available in pol. ellipse analysis group result) we can get the same pol. state shown in this figure.

Using the definition from equation 10 here , https://www.waves.utoronto.ca/prof/svhum/ece422/notes/03-polarization.pdf . Its giving back same major angle but ratio is not same.
• Guilin Sun
Ansys Employee
You can either using that analysis group to get Gp, Gs, or using grating analysis with your own script to get the farfield vectorial fields of Gp and Gs. Please refer this script
https://support.lumerical.com/hc/en-us/articles/360034407034-gratingpolar-Script-command
To count for all the grating orders this script gives results in spherical coordinate. you will need to extract the fields at the specific theta,phi to get the complex valued of Ep and Es. Please note that this is different to plot ellipse polarization. I would suggest you to read the scripts in the analysis group, get to know how does it work to get the ellipse and how to get the Ep and Es at the diffraction angle (diffraction order) .