Hi. I think you are not injecting the proper mode into your fiber. You can use ports as your I/O ports. Check "Dielectric Slab Waveguide" example in Comsol.

Thanks@Seyed Hadi Badri for the answer. I am using numeric ports as I/O ports. I am using electromagnetic wave beam envelope (ewbe) not electromagnetic wave frequency domain (ewfd). It has the setting of input power not mode and the power is set as 1W in my case. The "Dielectric Slab Waveguide" is solved using ewfd. Since, I will have fiber length in cm so I am using ewbe. I tried with ewfd but the length requirement should be in

Hi. If you use the "Circular" or "Rectangular" port type in 3D or 2D simulations then you would have the "Mode type" option. If you are still having a problem, you can send me your simulation file.

Hi Seyed, I tried using the circular ports as you suggested. I am getting error - "Two points describing the axis vector need to be defined properly". In my opinion, the mode type (TE) in circular port settings should not be used because I am calculating a single mode fiber structure which supports HE11 mode.

I would like to share my file. I am following this from the given COMSOL example/tutorial on rectangular waveguides.

Hi. Unfortunately, I am busy for a while and it may take long time for me to check your simulation file. However, I have a proposal for solving your problem. I also had a problem in exciting a certain waveguide in Comsol. I used Lumerical to find the proper excitation mode. Then I exported the mode as Text file. You can import the electric field components as interpolation functions to Comsol. Afterwards use "User defined" ports and define your electric field components. I hope this solves your problem.

Thank you very much @Seyed Hadi Badri for your solution. I was also busy in solving this. I would like to share that the error was due to defining the cylindrical waveguide. COMSOL takes propagation direction in x-axis while I was defining it in z-axis. Now, it is working.

Hi. I don't understand what you exactly did to solve it. Please share your simulation file if it is possible. Thank you Suchita Yadav .

Hi, I modified the cylindrical co-ordinate and set x-axis as propagation direction (length of the fiber) and y & z are fiber cross-section. Check the axis in the attachment. New one is working.

Thanks.

Hello Suchita Yadav Could you advice, how you could change waveguide orientation ? If you could share modified *.mph , I would appreciate. Thank you.

Hello Seyed Hadi Badri .

Could you please attach any sample of "Ex.txt" to be imported acceptable for problem under discussion? (or just 1 string to understand the format). Thank you very much.

I attached a sample "Ex.txt" which is exported from Lumerical. Then you need to convert it to a rearrange the data so Comsol can read it. I also attached this file (ComsolEnteryEx.txt ).

Here's a Matlab code to convert these files:

%% This code is written by Mohsen Mohammadzadeh Gilarlue

function ImportMode()

close all

figure

[x,y,Data] = ReadModeFile ('Mode/Ex');

[x2,y2,Data2] = ChangeResolution(x,y,Data,200);

Ex = Convert2Scattered(x2,y2,Data2,'ComsolEnteryEx');

subplot(221);pcolor(x2,y2,Data2);title('E_x');

clear x y Data x2 y2 Data2 Data_scattered

end

function [x2,y2,Data2] = ChangeResolution(x,y,Data,res)

[x2,y2] = meshgrid(linspace(min(x),max(x),res), linspace(min(y),max(y),res));

Data2 = griddata(x,y,Data,x2,y2);

end

function [x,y,Data] = ReadModeFile(fileName)

if nargin ==0

disp ('hello');

[file,path,indx]=uigetfile('*.txt');

if indx == 0

errordlg('You did not selected a file');

end

file_name = [path,file];

else

file_name = [cd,'\',fileName,'.txt'];

end

f_name = fopen(file_name);

lines = textscan(f_name, '%s', 'Delimiter', '\n');

lines = lines{1};

blank_lines = find(cellfun('isempty', lines));

x = str2double( lines( (blank_lines(1)+2) : (blank_lines(2)-1) ) ) * 1e-9; % nm

y = str2double( lines( (blank_lines(2)+2) : (blank_lines(3)-1) ) ) * 1e-9; % nm

Data = str2double(split(lines( (blank_lines(3)+2) : (blank_lines(4)-1) ) ) ) * 1 ;

Data = Data.';

end

function Data_scattered = Convert2Scattered(x_grided,y_grided,Data_grided,name)

Data_scattered=[x_grided(:),y_grided(:),Data_grided(:)];

save([name ,'.txt'], 'Data_scattered', '-ASCII','-append');

end

Dear Vladimir G. Toshinsky

Please let me know if you need any further information.

And to change waveguide orientation, you need to change "Axis type" as shown in the attached figure.

Dear Seyed Hadi Badri

Thank you very much for prompt support. I really appreciate that.

You're welcome.

Dear Vladimir G. Toshinsky

My Comsol's version is 5.4 so I cannot open your mph file. However, from the figures you shared, I noticed that you considered that Ez, Ex and Ey are the same (int1) which is wrong.

Dear Seyed Hadi Badri

Thank you very much for pointing inaccuracy . I made modification (attachment), but calculation stop with error after that. If you have any comment, I would appreciate.

Dear Vladimir G. Toshinsky

There is something wrong with your port1, however, I cannot figure it out from the picture. I may be able to help you if you send me the m file of your project. Please follow the steps in the attached figure. First you should "Compact History", then save you mph file as m file. Send me the m files of this and previous project.

Dear Vladimir G. Toshinsky

Hi. I uploaded the corrected mph file. Please note that I used numerical ports.

You're welcome.

Tq, best explanation. Good for me too.

Hi Parisa Borjikhani

Please refer to Comsol's example "fiber simulator" in the "Application Libraries". Then go to its "Model Builder". This may be a good starting point for you. And the following links may be helpful:

https://www.comsol.com/blogs/step-index-fiber-simulation/

https://www.comsol.com/model/step-index-fiber-145