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In this work, we describe a theoretical approach for combined thermal, mechanical and optical simulation and analysis of planar polymer waveguides. We consider a finite element approach for thermal and stress/deformation simulation. Also, a Crank-Nicholson finite difference beam propagation method (CN-BPM) is implemented to perform the optical simulation. The results of the finite element (thermo-mechanical) analysis are coupled with the CN-BPM results to carry out the optical simulation of poly(methyl methacrylate) (PMMA) waveguides as function of temperature. For thermal simulation, a model was designed where a polysilicon microheater was added to the upper cladding of the PMMA waveguides to vary the temperature between 20 • C and 200 • C. Thus, the impact of the induced temperature gradients on the refractive index modulation of the PMMA waveguides and the corresponding change in numerical aperture are obtained. In addition, the temperature gradients influence the beam intensity profiles and the movement of the primary eyes within the optical waveguides, thus, impacting the optical properties. Furthermore, the thermally induced mechanical stress and deformation were calculated for transverse and axial directions. In the next step, validation of the model by systematic experimental studies will be performed. In general, our approach provides a toolbox for more comprehensive multi-physics theoretical analysis of polymer-optical waveguides which, in future, can be extended to more complex and functional structures as required for flexible sensor networks, as example.

Straight and bent self-written waveguides (SWWs) are formed within a photomonomer mixture by means of a self-trapping effect when a single laser beam or two laser beams with tilt are propagated inside. These SWWs can be used as optical interconnects in integrated photonic circuits if two laser beams are launched in opposite directions into the photomonomer. In this work, two kinds of photo-polymerization models are implemented to simulate the SWWs. In the phenomenological model, the refractive index increases directly with actinic laser intensity, whereas the diffusion model has a more complex variation of refractive index profile which takes into account the individual redistribution of mixture components. Both these models are linked with a Crank-Nicholson based Beam Propagation Method (CN-BPM) to simulate the time varying light distribution within the polymer coupling structures. Differences are observed in the numerical simulation results for straight and bent SWWs with respect to the temporal evolution of refractive index within the mixture, corresponding beam intensity profiles and curing time. In addition, we show that a saturation of refractive index change leads to the polymerization of surrounding monomer and, as consequence, to corrupted light guiding. We report on the minimum refractive index modulation that is required for optimal light guiding within the SWW.

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