The positions R and T monitors and other questions


#1

Hello dear all
In my structure I want to consider the optical properties of one nanowire that is clamped from both sides by platinum and aluminum on silicon substrate ; so, I have some questions about my structure:

  1. I don’t know the geometry of fdtd effects on my results or not?.
  2. Distance of source ( I have only used laser source with wavelength 633 nm) and R and T monitors from the nanowire as object.
  3. The Positions of R and T are right or not like figures 1 and 2, which one is right?
  4. I have used PML and plane wave in my structure; so, is it right?
  5. How can I get the results like band structure, photon energy and lattice parameter?


#2

I’ll answer your questions in order:

  1. The size of the FDTD simulation region can affect the results. For example, if you want to simulate the Si substrate which is semi-infinite, the size of the simulation region and the size of the Si substrate should be set up so that the substrate extends up to the boundary of the simulation region. If there is some space left between the substrate the simulation region boundary, this would simulate a finite-sized block of Si where there will be reflections between the interface of the Si and the air next to the Si.

  2. The distance of the source from the structure should not make a difference to the measured reflection and transmission unless you use something like a beam source since the beam source has a specified focus position, so moving the position closer or further could affect the field profile of the beam when it strikes the structure.

  3. The placement of the monitors in Figure 1 should be correct.

  4. Using PML boundaries at the sides of the simulation region with a plane wave is not recommended since it leads to edge effects as shown in example 3 on this page:
    https://kb.lumerical.com/en/index.html?ref_sim_obj_planewave_edge.html

Instead, if the structure is not periodic, a TFSF source can be used. If the structure has periodicity, periodic or Bloch boundaries can be used with the plane wave source. More information on the simulation setup for different types of devices is discussed in the video here which I would highly recommend viewing:
https://www.lumerical.com/solutions/materials/video/introduction_plasmonic_simulations.html

5.The method for calculating the bandstructure of a periodic structure and example simulation files can be found in this section of our online Knowledge Base:
https://kb.lumerical.com/en/index.html?diffractive_optics_pc_bandstructure.html


#3

Dear nlui, thank u so much according to the very good recommend, could u please tell me about the figure 1, if I want use TFSF source, the positions of R and T are right or not? I need the data like Transmittance and reflectance.


#4

A post was split to a new topic: Do I have to determine both n and k values when importing a new material(ZnO)?


#5

Dear Nancy
Hello and good time
In my structure ( single nanowire) the results of transmittance and reflectance are suitable or not?
If not please tell me which results are suitable?
Thank u so much


#6

Hi Ali,

This is a good question since you have a single device, the setup that you use could depend on the result that you are trying to collect. If using a TFSF source, the source will have a finite area where the source is injected. Using a frequency domain power monitor or profile monitor placed outside of the TFSF source region, you will measure the transmitted and reflected light which is scattered by the nanowire and any other structures which are fully contained within the TFSF source region. Since only the scattered fields are present outside of the source region, the results won’t include light which is directly reflected or transmitted through the substrate as shown in the “Testing your setup” image on this page:
https://kb.lumerical.com/en/index.html?ref_sim_obj_tfsf_sources_usage.html

You can see that there is basically no light outside of the source region even though the source is incident on a substrate.

If you would like to collect the total light which is reflected and transmitted including light which is directly reflected or transmitted through the substrate, you may want to use a different finite-sized source such as a beam source or custom import source which is set up to match the properties of the source that you would use experimentally such as a laser source.

If you do use a TFSF source, one thing to be careful of is to place the reflection and transmission monitor far enough away from the source boundaries that the monitors do not overlap with the white shaded region around the source boundaries as described here:
https://kb.lumerical.com/en/index.html?ref_sim_obj_how_close_can_monitors_be.html

For Figure 1 of your second post, the transmittance monitor is exactly at the surface of the substrate, so if using the TFSF source the source would probably extend into the substrate, and in that case the transmittance monitor would need to be moved lower.


Nanoantenna - reflectance , transmittance monitor position
#7

Dear Nancy.
Hello and good time.

At first I don’t know how to thanks you; so, I wish u reach to all of your wishes. Your recommends are very very useful to me. I have a request, could you please check my model as I sent u the file? because I want be sure my procedure is right or not?

Thank u so much
Best Regard
AliDouble clamped ZnO optical Ali .fsp (276.9 KB)


#8

Dear Nancy

I have sent you the file of my simulation, could you please check and then if there is some problem correct the file and transfer it?

Thank you so much
Best Regard
Ali


#9

Dear Nancy.
According to your recommend about lase source like experimental, you told me that it was better use beam source or custom import source; hence, could you please set up my model according to your recommend?
I am so sorry such as this request.
Double clamped ZnO optical Ali .fsp (276.9 KB)


#10

Hi Ali,

The beam source (or import source) that is specified depends on the properties of the source that you would use experimentally. Without knowing the details of the source, it would not be possible to set up the source in the simulation.

The parameters used to define the beam are defined in the “Beam options tab” section on this page:
https://kb.lumerical.com/en/index.html?ref_sim_obj_sources_plane_waves_and_beam.html

If the beam waist size is several times larger than the source wavelength, you can choose to use the scalar approximation beam where you can specify the source using the beam waist radius and the distance of the source from the beam waist, or you can specify the beam radius and divergence angle.

If the beam waist size is on the order of or smaller than the wavelength of the source, then you can use the thin lens beam where you need to specify the numerical aperture of the beam and the distance from focus.

If the laser used in your experiment cannot be represented by a Gaussian beam, you could specify the beam by using the import source and importing the field profile of the beam. There is a tutorial showing this here:
https://kb.lumerical.com/en/index.html?ref_sim_obj_custom_source_profile_from_oth.html

Hopefully one of these options would work for you.


#11

Dear Nancy.
Hello and good time.

Could you please give me recommendation according to the below list:

  1. I want to use Gaussian or Import source; so, which figures are right to set up my structure (Figures. 1 and 2 . or Figures3. and 4.)?

  2. PML boundary condition is suitable or not?

  3. There is only n=2 for bulk ZnO nanowire; so, there is no k value for it; hence, If I want to define k=0 is right or not?

  4. There is no data of ZnO material inside the software; therefore, I have to determine the values of n and k for the bulk ZnO, After clicking on the (n, k) Material ( first option at above) it would be opened like Figures 5 and 6, after clicking on Sampled data ( the one before last option) it would be opened like fig. 7; so, which one is right to determine the value of n and k?

  5. If the Sampled data is right, Should I change the values of tolerance, max coefficients and wavelength or as default is right ?

  6. According to the Gaussian source like figures. 8 and 9. Should I change the values of waist radius, distance from waist, beam radius, divergence angle and NA and distance from focus or as default by the software is ok?

  7. According to the Import source like fig.10.Should I set up the Imported source setting or not?

Thank you so much
Best Regard
Ali











#12

Dear engineer.
Hello and good time.

Thank you so much according to the great recommendations of n, k values for the ZnO bulk material. Actually, In my model, I want only consider effects of reflectance and transmittance via single wavelength of laser (633 nm); so, which one is suitable to define only n value ( Fig.1 or Fig. 2 ):

Thank you so much
Best Regard
Ali


#13

Hi @alivazinishayan,

If you’re considering single frequency range, it’s easier to type the refractive index (n) as 2.0 in index blank when you select “〈object defined dielectric〉” feature in a Material tab (Optical material - material) from the Edit rectangle windows (Fig. 1) than to register “(n,k) Material” in a Material Database window (Fig. 2). Selecting the registered “(n,k) Material” in the Material - Optical material in the Edit rectangle window, generally the material fitting procedure is needed to confirm the fitted data of complex refractive indices (n,k) based on a multi-coefficient model (MCM). On the other hand, the “〈object defined dielectric〉” feature do not require a material fitting procedure, because the refractive index (n) is a constant not dispersive.

I would like to recommend you to start up the silver nanowire tutorial, one of the excellent examples for newbies. If the ratio of the length to diameter of nanowire is larger than, i.e., 100, you might consider the 2D simulation that is much more time and memory efficient approach than 3D one. This AgNW 2D example teaches how to set up the TFSF (total-field scattered-field) source and monitors to calculate the absorption, scattering, and extinction cross-sections. You can learn a lot of fundamentals and some important FDTD techniques from it.

I hope it could be a helpful guideline for you.


#14

Dear isawjsy
Hello and good time.

I have simulated single ZnO nanowire to investigate effects of mechanical properties on the optical properties like transmittance and reflectance; hence, at first it is considered without mechanical stress and strain; so, I got the results as i mentioned. For the second part, after simulation ZnO nanowire under loading condition using ABAQUS and importing STL file format to the FDTD solution, unfortunately I got the same results; so, I am afraid about the correct set up of my structure by FDTD, could you pleas guide me how i can solve my problem?
It should be noticed that, to getting the transmittance and reflectance results, i have right click on the both monitors and then choose option T, respectively; so, is it right?

Thank you so much
Best Regard
Ali


#15

@alivazinishayan

I am not familiar with ABAQUS. Does this simulate a physical deformation of the shape of the structure which you then importing into FDTD Solutions, or does it simulate the stress-strain profile?

If it is calculating the stress-strain profile, you would first need to convert the stress into a change in refractive index of the material due to stress and load it into FDTD Solutions to see the result. Here’s and example which shows that:
https://kb.lumerical.com/en/index.html?other_application_stress_strain.html

Regarding getting the transmission and reflection, the “T” result from the monitors is appropriate because it gives the net power flowing through the monitor.


#16

Dear Nancy.
Hello and good time.

First, thank you so much according to the good recommendation. Actually, the results of simulation using ABAQUS are including physical deformation of the shape of the structure and stress-strain profile; so, the problem is how i can consider effects of stress and strain on Refractive index, while there is only one value for the bulk ZnO (n=2); hence, there are two questions:

  1. How can I convert stress into the change of Refractive index as regards n value of bulk ZnO is 2.0; therefore , which equations are appropriate, as shown below. So, n means that new value after mechanical stress or not? What is parameter of R in the equations.

  2. To getting effects mechanical stress on my structure, Should I import the only new value of n into the FDTD ?

  3. Do I need import physical deformation of shape from ABAQUS into the FDTD after mechanical stress?

Thank you so much
Best Regard
Ali


#17

Dear Nancy.
Hello and good time.

To mechanical stress, I have considered Von Misses stress; therefore, according to the equations of stress conversion into a change in refractive index of the material due to stress and load it, actually, I don’t know which directions of stress is appropriate. It should be noted that the direction of mechanical force is y; so, it is typically that stress is considered as Von Misses stress.
Could please guide me?

Thank you so much
Best Regard
Ali


#18

Dear Nancy.
Hello and good time.

Could you please check up the simulation of my structure, whether it is set up correctly? It would be sure if it is set up correctly.

Thank you so much
Best Regard
Ali

1.2.fsp (276.8 KB)


#19

The simulation setup looks good, but the memory requirements to run the simulation are very high. I would recommend moving up the x min boundary of the simulation region to reduce the volume of the simulation to help reduce memory requirements.

As well, because the structure looks like it is symmetric, you could also apply symmetry in the boundary conditions in the x and y directions to further reduce memory requirements:
https://kb.lumerical.com/en/index.html?ref_sim_obj_symmetric_anti-symmetric.html

You could also consider using the mesh override region just over the smaller structures, so that a coarser mesh can be used in the substrate and in the air above the structure which would also reduce memory requirements.

If you want to simulate the results for the structure under stress, then the physical deformation of the structure, and the change in refractive index due to applies stress are two effects that could be included in the simulation. However, depending on the particular case, you may not need to include the effects. For example, the stress and strain example here assumes that the change in the shape due to bending the structure is very small, so the deformation of the shape of the structure is not included in the simulation:
https://kb.lumerical.com/en/index.html?other_application_stress_strain.html

If the change in refractive index of the ZnO is small due to the applied stress, then it’s possible that you could exclude this effect. Unfortunately I don’t know the details of the calculation of the change in refractive index due to applied stress for ZnO with Von Mises stress, so it might require looking into it in more detail. The equations from the stress and strain example in the Knowledge base are for the particular case where the structure is bent with a specified bending radius R, so the equations in your case may be different, but the main idea of using the n,k import to import the refractive index over space for the structure with applied stress is the same.


#20

Dear Nancy.
Hello and good time.

Thank you so much according to the best recommendation. I have two questions:

  1. Actually, I don’t know why after changing the value of Refractive index in my structure according to the effects of stress on n value, I get again the same result like free-stress.

  2. I have changed the cross-section of ZnO like circular and rectangular and also the value of their diameters; therefore, I get again the same results like hexagonal cross-section of ZnO nanowire with small diameter.

So, I would to know if there is problem in my simulation or the results are right?

Thank you so much
Best Regard
Ali