Refractive index profile

[rahman sharaf]

Hi,

I would like to define a rectangular waveguide which its refractive indices along x and z axes in OptiFDTD,
i.e. along vertical and horizontal axes, set through a special function.
I wonder if anybody can help me how should I do this?

Thanks.

[Scott Newman]

I just want to clarify what you are asking for as I am not certain. If you can answer the following questions I can better help with the problem.

1. Is this a 2D or 3D design?
2. It sounds like you want the waveguide cross-section in the xz plane and the propagation in the y-axis, is this correct?
3. Do you want your script changing the refractive index profile along the propagation length of the waveguide or to specify a complex cross-sectional profile?
4. Are you looking for regions of constant dielectric or is this special function you are using needed to produce a graded refractive index structure?

Scott

[rahman sharaf]

Dear Mr. Newman,

Thank you for your attention.
My structure, in general, is three dimensional, its cross section as you mentioned is in the x-z plane and propagation is along the y axis.

The problem is that I want to introduce anisotropic refractive indices along x and z directions. I need that along x axis, the refractive index to be a Gaussian profile and along z axis it has an exponential profile. Along propagation direction (y axis) the refractive index is a constant value.

So for clarification I would like to inform you that:
1- my design is 3D.
2- Cross section is in the x-z plane and propagation is along y axis.
3- I need a Gaussian refractive index profile along x axis and an exponential profile along z axis while along propagation direction (y axis) a constant refractive index must be set.

Thank you so much for your time.

[Scott Newman]

Rahman,

A couple of points to what you are trying to do.

1. OptiFDTD is designed around propagation along the X or Z direction, which means your cross sections will need to be XY or ZY.
2. The way materials are handled within OptiFDTD you would need to create a script that creates points of material at each grid point where the points are calculated to give the profile you want. This can take time but would give you what you want, have you worked with our scripting engine?

[rahman sharaf]

Dear Mr. Newman,

Your comments are great and I appreciate your attention.

You are right about propagation direction in the software.

By script engine do you mean “layout script”?

With layout script I have created periodic structures such as gratings as well as other components including observation points and input illuminations.

Do you mean that I should define a waveguide for each point of my structure with desired refractive index and then in the layout script, I arranged them in the locations to create the profile?

Can I change a refractive index of a grid point in my design with scripting directly without a predefined waveguide in the “PROFILES AND MATERIALS” section?

[Scott Newman]

Rahman,

Unfortunately you would need to create a material definition for each change in the refractive index. The positive is that we allow material import through xml files, and multiple materials can be in one xml file. Depending on if you are using a licensed version or the free 32-bit you can find examples of in your material library located in your documents folder. This would allow you to automate the material creation through matlab, excel or some other third party processing utility. You could then us VB script to create partially overlapping 3D cubes and assign the required material.

As a secondary questions what is the relative refractive index differences? We have a product OptiBPM that does allow native graded materials specifically for waveguide modelling. However, the basis of BPM is that the guide is weakly guiding.

Scott

[rahman sharaf]

We implemented a matrial with a relative index of 1.59 and an index difference of 0.006.

It will do this just as you mentioned and I hope I can do.
Thank you so much for your valuable help and your time.

[Scott Newman]

That should be well within the range of feasibility for OptiBPM which can do the kind of profile you are looking for.

Scott

[rahman sharaf]

I appreciate your support and I will try optiBPM.

[Author]

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