Which Module should I choose?

[Arin Immo]

I want to deal with the problem:  A Guassian beam transports into a fibre from one end ,I want to know how it behaves at the other end  ,which  physical module should I choose?The " Mathmatics"  module  or the "  RF" moulde，or  another one?

[Pavel Dergachev]

Лучше, для начала выбрать "RF". (там уже введены уравнения и граничные условия)

В "Mathmatics" все придется задавать самому - этот модуль нужен для случаев, когда не хватает функциональности стандартных модулей.

[Arin Immo]

But how to define the incoming field as  a Guassian beam  in RF module? It seems impossible! Can you give me your email address? I will send you my file about it( because  to upload my file directly is very slow)! something wrong with it!

[Pavel Dergachev]

Посмотрите на стандартные примеры из COMSOL:

http://www.comsol.com/showroom/gallery/955/

http://www.comsol.com/showroom/gallery/956/

UPD. Если проблемы с присоединением файла, попробуйте выложить на любой файлообменник.

[Arin Immo]

I have met the error!  in the "Guassian .mph"->"Electromagnetic  Waves,Tansistent2"->"Scattering Boundary Condition1"->"Scattering Boundary Condition",  when I set E0,the yellow text tells: Unexpected unit of input.   What does it mean?

And you  go  "study 2" ->"compute",there will be another error!

[Arin Immo]

I follow the file  in the attachment step by step!

[Arin Immo]

The second error lies in "Electromagnetic  Waves,Tansistent2"  ->"Wave Equation ,Electric 1"->"Electric Displacement  Field "

[Pavel Dergachev]

1. В "Wave Equation, Electric 1" должно быть <d33*temw2.Ez^2>

2. В "Time Dependent" должно быть что-то похожее на <0 61[fs] 90[fs] 120[fs]>

3. В "Scattering Boundary Condition 1" Warning можно смело проигнорировать.

[Arin Immo]

http://www.youtube.com/watch?v=DkY4vaKo72wYes! It  works!  what dose the term "perfectly   matched layer"  mean?And in which condition I may use it?

[Arin Immo]

  I have met the error "There is no feature using these setting" when i go "mesh" -> "size 1", why does it happen?      And if you go "mesh  1"->"FreeTetrahedral  ",there will be another error,why?

[Pavel Dergachev]

У меня вроде все работает - я перешел на версию 4.3b.

[Arin Immo]

Welcome back! You must be very busy these days! I have met a lot of troubles and I finally overcome them!  However ,I don't know why the Electric field was always 0  whichever  study I use in 'RF'  module!  Maybe because I'm confused with"  wave equation    ,electic"   "Electric  field"  , it seems that they can't coexist  ,or they will override each other!

By the way,  how  did you switch it to 4.3b?  I  know  there is a  new photonic  module in it which may solve my stuff better!  I need it!

[Pavel Dergachev]

У Вас геометрия разделена на 2 части и я не вижу условий сочленения геометрии в уравнениях.

Вероятно это и есть причина проблем.

http://www.comsol.com/products/4.3b/

http://www.comsol.com/products/wave-optics/

[Arin Immo]

I have been with the problem for five days! I still can't work it out !What conditions should I add to the joint geometry equations?

[Pavel Dergachev]

Попробуйте геометрию собрать в виде "From Union", вместо текущего "From Assembly".

[Arin Immo]

It doesn't work  either!  O h,God! Where is the way  out?

[Pavel Dergachev]

Попробуйте использовать "Electromagnetic Waves, Transient".

[Arin Immo]

It works !  I have met some small   problems

[Arin Immo]

what does "From parent"(Picture 2)mean?  And when  I  plot something , why there is  the  only option"None"(Picture 1)?

[Pavel Dergachev]

1. Данные берутся такие как у его родительского элемента в дереве.

2. Видимо нет данных нужного типа.

[Arin Immo]

What do they mean of the options in boundary probe ?I  mean,for  example,the maximum  option,does   the solver  record the maximum value of Ez field in the boundary every time point?

[Pavel Dergachev]

Максимальное, минимальное и среднее значение указанной величины на выбранной границе, в каждый момент времени.

[Arin Immo]

for the output surface, I want to define it without reflection,   which boundary   condition   should I use,the scattered one or the initial one or anther one ?  These days I'm considering the appropriate boundary condition for the   solid!

[Pavel Dergachev]

Мне сложно ответить на вопрос - я практически не занимаюсь задачами такого типа.

Надо разбираться, что бы сказать точно, а на это нет времени.

[Arin Immo]

You must be  very tired! It seems that you are the only one answering questions  for us!  Thanks for all you have done for the forum!

For the last question, I mean this:  It's  a periodic boundary condition of  Bragg fiber structure!

 From the innermost boundary to the exterior boundaries 

at the first innermost boundary ,the transverse  electric field is 0,at the second boundary ,the electric field is minimum,  the other boundaries  follow  the two boundaries on order

so,what boundary conditions should I define  for the two boundary respectively?

[Pavel Dergachev]

Геометрия должна быть "From Union".

[Arin Immo]

I don't understand why there is negative  value of (emw.Ez) ^2 in the figure! There may be imaginary part in "emw.Ez" . But what is the physical meaning of  the imaginary part   of Ez? And if Ez is a complex number,  how to get the module of Ez  ?

[Arin Immo]

What does (-nz)mean? Does it indicate the direction of the surface? 

[Pavel Dergachev]

Модуль -> "abs()"

Мнимая часть -> "imag()"

Мнимая часть -> "real()"

"nz" - z компонента вектора нормали к поверхности

[Arin Immo]

for Nz ,If I want to  indicate  a certain direction ,should I put a specific value for Nz  or just let it be Nz?

[Pavel Dergachev]

Задается направление, наверное просто "nz".

[Arin Immo]

How should I deal with the Error:

Errors during multiphysics.

Automatic scaled regions cannot treat selections without exterior and interior boundaries.

- Feature: Perfectly Matched Layer 1 (pml1)

 

[Pavel Dergachev]

Неправильно задан PML, я не могу сказать большего, чем уже написано.

Для него видимо надо выбрать внешнюю и внутреннюю границы.

[Arin Immo]

Please help me with PML settings  of the file! I don't know where my settings are wrong.

[Pavel Dergachev]

Пожалуйста:

[Arin Immo]

First, I can open the file because of lower   comsol  version. Can you cut some pictures to show where you have made corrections ? 

Second, In 3-D situations ,I just can't use PML under the condition that I make the geometry an "Assembly"  ,It shows me the same error as above .Please help me with it ! I need the "Assembly",in that I can must the boundary condition "continuity",how to achieve that?

[Pavel Dergachev]

1. Не надо использовать сборку и "continuity". Это необходимо когда геометрия двигается.

2. PML не должен содержать границ с "continuity" и все будет работать. Я просто добавил внутреннюю границу в последний слой (без "continuity").

3. Тоже и в 3D.

Зачем Вы постоянно пытаетесь использовать "continuity"?

[Arin Immo]

I just want to make the boundary consistent  for electric field at each layer ,I wonder if a "union" satisfies the requirement  as default ??

[Arin Immo]

And which  kind  of material  should I use  for PML ? the same with the outermost layer ,or the air core or another arbitrary  one? 

[Pavel Dergachev]

Правильные граничные условия будут и без "union".

Если просто сделать геометрию как union - все будет работать.

Только надо сильно уменьшить сетку - она была слишком грубая.

[Pavel Dergachev]

PML должен быть из какого-то линейного материала (с постоянными коэффициентами) - вроде это главное условие.