How to model the Bragg Wavelength shift caused by an applied load

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Hi everyone,

I am trying to simulate the shift of the Bragg Wavelenght in an optic fiber caused by an applied load. I am using COMSOL version 5.3a. I simulate the deformation of the fiber caused by the load using the physics "Solid Mechanics" and the load is applied as "Point Load" on the cladding of fiber. In this simulation i checked the option "Inclued non linearity" to later export the deformed geometry.

Then i export my deformed geometry and i import it in a second project for the optical study using the physics "Beam Envelope". I remesh the geometry, delete the outer cladding (to simply the simulation) and define the PML. I define the refractive indexes of the core, cladding and PML using the equation i found in the COMSOL tutorial "Stress-Optical Effects in a Photonic Waveguide". The stress used in the equations is imported from the "Solid Mechanics" model using 3 interpolation function i called (sx, sy and sz).

The results i obtain (attacched) don't match with the theorical result and with the results i obtain in FBG-SimPlus (also attached). Anyone can tell me what i am doing wrong? Are the equations wrong or is the entirety of the approach?

The projects are too big to be attached sorry.

Also sorry for my english.



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