Learning Forum

[anindya]

Dear Experts,

For some specific reason, I would like to measure and plot the phase spectrum of an incident optical signal as a function of refractive index of a certain medium but I am unable to find any monitor in FDTD which can measure the phase spectrum.Is there any way to do such this? I wish to see the change in phase spectrum by sweeping the refractive index.Kindly suggest a possible solution.

 

Thanks and regards,

Anindya Bose

[Guilin Sun]

I am not quite sure what exactly you want to get. you want to get "phase spectrum as a funtion of refractive index"? usually the phase and the refractive index is a function of frequency or wavelength. Since both can be nonlinear and monotonically change, I am not sure if you can use refractive index as the absissa. Once you get both of them as a function of frequency/wavelength, you could try to plot phase as a function of refractive index (most likely the real part).

probably you can sweep refractive index, could you later find a material with specified reftractive index as the function of frequency?

If you want to see the map of phase vs frequency and swept refrative index, you can image them:

image(f,index,phase)

where f is the frequency of the source;

index is what you swept;

phase is what you get from a monitor, most likely it is a line monitor. If it is 2D monitor, then you will have 3D matrix result that cannot be directly imaged.

Phase is always associated with field components. For example, if you want to get phse of Ex from a xy plane monitor , you can

E=getresult("monitor","E");

x=E.x;

y=E.y;

f=E.f;

Ex=E.Ex;

phase_x=pinch(angle(Ex)));

then phase_x will be a function of x,y and f.

Please try.

[anindya]

Dear Mr Guilin Sun,

Thank you for your response.I am particularly looking for a time dependent refractive index model where I can vary the refractive index with time and can visualize the change of phase at the output due to that.A Lumerical  link is provided below where it is mentioned but I am unable to get that model in the Lumerical mode.

Link: https://www.lumerical.com/learn/whitepapers/flexible-material-plugins/

Can you please suggest me where exactly I can get the feature.

Thanks and regards,

Anindya Bose

[Guilin Sun]

The time dependent refractive index can be found here  https://optics.ansys.com/hc/en-us/articles/360034394734-Advanced-and-custom-optical-material-models-in-FDTD-and-MODE

Since plugin material is advanced feature, we provide very limited technical support.

However, since it changed with time, you will need to use time monitor and complex source field:

to get real and imaginery parts of the fields in order to get phase information. Frequency-domain monitor can only give steady-state CW phase.