FDTD reflectance measure

[park sun geun]

Hi.
I am a student who is studying optoelectronics at graduate school.
We have just written and have written to help solve the problem.
Using a translator, the language can be awkward.

What I tried was to shoot a white light on the photonic crystal and see the reflectivity along the wavelength. But I faced many problems.

First, I could not find a way to shoot the light in the visible ray area at one time.

The second is to give the correct amount of light. For example, I would like to give a photonic crystal of exactly 1W of light and how much light is reflected.
(I guess I was just shooting a continuous light.

The third is linked to the above. I want to see the total amount of energy in the area detected in the observation area. Of course, since it is seen in the visible ray area, I wonder if I can see it as lm (lumen) considering the visibility characteristics.

I would like to see the amount of light reflected and placed on the photonic crystal as shown in the attached figure.

Please let me know if there is anything need to see the reflectivity of photonic crystals.

In addition, the size of the photonic crystal was made to be 100 nm, and the size of the grid to 197 nm. Then, just by moving the structure, the program stopped and shutdown. I would like to know if there is a problem with the specification of the computer or something else.

The version is 14.0.0.1205.

[Scott Newman]

The translator did a weird job as many of your comments are not clear and we need to clarify a few things

1. White light – I believe you mean a broadband source which is achieved by setting your source to be a pulse with a sufficiently short duration.
2. Visible ray area – Do you mean Visible spectrum?
3. Structure dimensions – You claim your photonic crystal is 100nm, this seems incredibly small. Is your entire crystal 100nm or are the holes in your crystal this dimension.
4. Grid resolution – You specify that your grid resolution (197nm) is almost double that of some part of your structure (100nm). Your resolution needs to be smaller than the smallest physical feature in order to properly define the space.
5. Source power – Setting the power to 1W is done by within the transverse tab of the source where you can set either amplitude or power. Is there something else you are trying to set?

Based on your description it is a bit hard to sort out where to even begin addressing your issues. Could you please attached your design file so that I can review what you have done?

[park sun geun]

I have more question.

How can I make to particular pulse?

I attach picture.

and Does observation area show the sum of all past light energy or average ?

How can I control the time of observation area?

I don’t know exact mechanism and control method of observation area.
I want to know.
The quality of the question is too low due to lack of knowledge.
please help me

[park sun geun]

Thank you for answer.

I attach file what i have done.

I try something. I set source that is like RGB white LED spectrum.
I want to see the reflectance, but the amount of reflectance has changed with time.
I guess observation area estimate average of light. is it right?
When i see sample file, that use power spectrum to estimate reflectance.
And i want to know power spectrum y axis. is it power(W)? And then what is mean normalization in power spectrum. I think it is a bit different from what I think.
In conclusion, I would like to see a change in reflectance per wavelength depending on the source I made while changing the photonic crystal.

And I choose sine-modulated gaussian pulse, but In simulation summary, Input type is Gaussian Modulated Continuous Wave. I want you to send me the exact amount.

If there is a sentence that you do not understand, please let me know.

[Scott Newman]

I have reviewed your questions as well as your designs and have a few comments and suggestions. Before I get to that based on your questions I would strongly recommend you watch the introductory webinars hosted on the Optiwave website (<a href=”https://optiwave.com/category/resources/webinars/”>https://optiwave.com/category/resources/webinars/</a&gt;), specifically look for the webinar week post which will have a collection of webinars. The OptiFDTD basics contains an example of a reflectance calculation for a dielectric half space.

1. The observation area performs fourier expansions at each of the mesh points for specific wavelengths. What you are seeing in the observation area is the coefficients of the expansions. You can control what wavelength you are examining along the toolbar. So the results you see are the cumulative effect of the entire simulation.
2. The simulation summary is incorrect, if you setup observation points (I strongly encourage you to put one observation point at the center of each observation area) you will see that the sources are in fact pulses.
3. Your sketch of your desired time pulse and its spectrum is off. The Fourier transform of rect is in fact a sinc function not a delta. The fourier transform of a infinite sine or cosine is the delta. Are you looking for a pulse (something with a finite spectral width) or are you looking for something with delta function spectral form? If you are looking for a spectral delta then the source should be a CW (continuous wave) simulation. If you want a pulse but for it to almost be a delta you should simply increase the FWHM on your pulse, as this gets larger the width in frequency will decrease.
4. The y axis of power plots is either W or a normalized quantity. The normalized value is the power normalized by the input which was set to be the key input (Input Plane 1 in your case). Because you have multiple sources you either need to run three simulations and superimpose them or export unnormalized data and normalize it yourself.
5. Your spatial resolution is set to the auto which is the largest possible and still be numerically stable. With the dimensions of your structure this is not enough. You can see this by examining the quality of your spheres in the XY and XZ planes of the 3D Refr_Idx_RE(y) viewer within OptiFDTD designer.
6. You simulation was not run long enough, see my comment above about placing observation points at each observation area. This lets you see the time evolving field at one grid point. If you do this you will see that the pulse only just barely reaches your transmission observation area. So the pulse has not completely propagated through the structure so your reflectance measurements are incomplete.
7. You will need to clarify your comment that “the reflectance changes with time”. What time? How long the simulation runs or are you saying each simulation has a different reflectance?

Before proceeding much further I strongly encourage you to explore the introductory webinars I mention above as they establish much of the basics of setting up an FDTD simulation.

Scott

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