Discussion Forum

Have you discovered what was happening?

I have the same problem now!

Thanks,

Felipe C. Salgado

Hi,

I APOLOGIZE BUT THE SYSTEM DOES NOT ALLOW ME TO UPLOAD THE FILES. Please contact me at samuele_lilliu@hotmail.it for the models.

I have noticed two things: few replies on this forum and many bugs in the COMSOL software. I would really appreciate if someone could have a look at the two models.

I am currently using the version 4.0a.

I am trying to simulate an optical fiber in 3D by using the same steps described in that 3D waveguide adapter. I would like to get a S21 plot vs frequency. For what I have seen, if you follow the same modeling strategy you get bad results.

The geometry is made of 2 cylinders, core and cladding (PLEASE SEE MODEL R12A):

GEOMETRY: coreRadius = 4.1 [um], claddingRadius = 125/8 [um], fiber length = 5 [um].

MATERIALS: I have defined two materials only with the refractive index, which are silica glass for the core (n = 1.46526) and doped silica gass for the cladding (n = 1.46).

ELECTROMAGNETIC WAVES:
- perfect electric conductor at the walls of the cladding;
- port 1 at the base of the core (input, numeric port, wave excitation at this port ON, power 1 W);
- port 2 at the other base of the core (output, numeric port, wave excit. OFF);
- scattering boundary conditions at the cladding 'rings' of the two bases.
- wave equation everywhere;

STUDY (here I follow what's written in that waveguide tutorial):
1) BOUNDARY MODE ANALYSIS at input port.
- Desired number of modes 6;
- Search for modes around 1.4625;
- Port name 1;
- Mode analysis frequency 1.9341 [Hz].
2) BOUNDARY MODE ANALYSIS at output port.
- Port name 2;
- the rest same as previous
3) FREQUENCY DOMAIN.
- a sweep of frequencies from 1e14 to 3.5e14 [Hz]

The simulation crashes and I get the following error message

THE FOLLOWING FEATURE HAS ENCOUNTERED A
- Feature: Stationary Solver 1 (sol1/s1)
- Error: Undefined value found

There is even an error in the error message... LOL. By the way I am not able to simulate frequencies between 1 and 3e14 [Hz] (I get that error message). When I use 3.5e14 Hz the simulation runs. However the fields are zero everywhere, which does not make sense. I don't see any propagating field in the structure (for the calculated mode and for 3.5e14Hz.

I have tried many things. For example different definitions of the input port: numeric, rectangular, coaxial, user defined. I have built a finer mesh for the core but nothing changes. I have modified the solvers. But nothing.

I have also tried to define the boundary conditions in a different way. So I have put the input and output ports inside the structure and defined all the boundaries of the geometry with a Scattering Boundary Condition (please see MODEL R10A). However, also in this case I don't observe any propagation.

Thanks in advanced for the reply,

SL

Here is the other file