Assuming "x" and "z" as the axes on which your 2D geometry is defined and that propagation of the main field is along the z-axis, a plasmonic evanescent wave should propagate along the x-axis. So, I would use the x-axis vector component of the field instead of the z-axis one.

Paulo Lourenço

Thanks for your respond.

I did not use the x component of electric field to calculate the EFR.

the propagation length is in the z direction, that's why I use the poynting vector in the z direction in order to calculate the evanescent field ratio and it is common.

The problem, as I said before, is I can not reach the optimum value for slot height and width.

Do you have idea to share?

Thanks in advance.

I am afraid not Parviz, only one correction to my previous statement. I wrote "... plasmonic evanescent wave should propagate along the x-axis ..." but I should have written "... plasmonic evanescent wave should drop off exponentially along the x-axis ...". There is no transfer of energy away from the surface (no propagation).

Denis Jaisson

my structure has been desined in 2 dimension using Comsol and I used mode analysis study to find modes and propagation constants. I calculated the evanescent field ratio using poynting vector (I mean time avarage power flow) in the z direction which Comsol gives you. Then I used surface integration of poyntig vector over slot and upper cladding region (which is air) divided by the same prameter over whole structure.

EFR`= surface integration(Pz)slot and air/ surface integration (Pz) whole structure

my purpose is to optimize the EFR versus slot height and width but I can not able to optimize these parameters.

I would be very thankful, if you can give me useful advices.

Denis Jaisson

if your meaning by 3D integral is volume integral, I would say no. it is not 3D integral.

I can not do the 3D integral because my structure is the cross section of plasmonic slot waveguide, so it is 2D. and the integral is the surface integral for both nominator (including slot and uppercladding) and denominator (whole structure).

what should I do?

what is your suggestion?

Denis Jaisson

Sorry for late response.

The structure as I said before, is the cross section of plasmonic slot waveguide. the integral in numerator is the surface integral which cover slot region and upper cladding (which form air or the gas) and the surface integral in denominator covers whole cross section (including slot region, upper cladding, two metal strip which surround the slot region and two lower cladding forming the substrate).

I have attached my structure in order to understand my meaning.

Hope your next advice helps me a lot.

Denis Jaisson

you mean that my structure might have no optimum value?

if I want to get the optimum value, what should I do?

another question:

regarding plasmonic material, the propagation length is really important.

How do you calculate the propagation length using Comsol?