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Hi,

I need to calculate effective refractive index along a fiber taper in order to calculate the localize Brillouin scattering parameters along the fiber taper. Is FDTD the best program to use?

### Responses (5):

• #11249 Participant

Hi,

I need to calculate effective refractive index along a fiber taper in order to calculate the localize Brillouin scattering parameters along the fiber taper. Is FDTD the best program to use?

• #11340 Lizzie Li
Participant

OptiFiber can calculate the effective refractive index of fiber taper. And you can define the taper you want to simulate.

• #11365 saima buzdar
Participant

Hi
Is the Modal index different from the effective refractive index ?
if yes then what does show the modal index value like :Mode 1 ( 1.35890436, 0.00000283 )

Thanks

• #11369 Lizzie Li
Participant

Yes, mode index is different from the effective refractive index. After defining the fiber, you can get the effective refractive index by calculating modes.

• #11382 saima buzdar
Participant

In OptiFDTD after modes calculation we get data like this:

[ Modes ] [ Modal Index ] [ Polarization ]
Mode 1 ( 1.35890436, 0.00000283 ) FVect TE
Mode 2 ( 1.35909016, -0.00000458 ) FVect TM
i want to know that what does modal index show?
How Effective refractive index is calculated in FDTD ?

Thanks

• #11760 Steve Dods
Participant

The definition of Modal Index seems to be consistent and well defined. Modal index is the propagation constant of the mode divided by the free-space wavenumber, k ( k = 2 Pi / wavelength ). Since Modal Index is the quotient of two wave numbers it is dimensionless, like refractive index. Effective Index is sometimes used to mean Modal Index, but that is a bad choice of words because Effective Index is a term used for other things too. Effective Index sometimes means a number that will be useful in characterizing a material when a 2D simulation will be used to approximate propagation on a 3D structure. That is why I always use the term Modal Index when referring to a number that represents the propagation constant of a mode. Less confusing/ ambiguous. As for how Modal Index is calculated in OptiFDTD, well, that is a long story. You can find it in Optiwave OptiMode documentation.