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In this example, we study a simple CorningĀ® SMF-28 fiber.  

 

Solvers

FDE

Associated files

fiber_smf28.lms

See also

Fibers

set calculation parameters

bent waveguide solver

fibers_smf28_screenshot_zoom81

 

First, we run the eigensolver at 1.55um to obtain the mode profile. The first mode is obviously the fundamental mode.  

fibers_smf28_E2

 

Notice that we have used symmetry boundary conditions in the X and Y directions.  Without using symmetry BC's, the eigensolver will find two 'fundamental' modes. This is because the fundamental mode is degenerate. Using symmetry BC's allows us select modes with a particular symmetry (or polarization), while suppressing modes with other symmetries (polarizations). In many cases, it is convenient to suppress some modes to simplify your analysis.  

 

Next, we can look for the wavelength where this device becomes multi-mode.  To do so, we must first disable the symmetry BC's, so we find all supported modes.  Next, re-run the solver at a much shorter wavelength (such as 1um) where the device is known to be multi-mode.  Next, switch to the frequency sweep tab and run a sweep, tracking all modes, from 1um to 1.55um.  The results are shown below.  

 

fibers_smf28_multimode_cutoff_zoom44

 

The frequency sweep shows that the effective index of the 2nd order mode (yellow line) drops below the refractive index of the cladding around 1.3um.

 

It is possible to simulate the behavior of a bent waveguide, however the CAD will not show the bending. Please refer to the following pages for details, set calculation parameters, bent waveguide solver.

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