Discussion Forum

Greetings.
The proposed coupler consists of two layers. the bottom layer comprises one-single mode silicon waveguide embedded in sio2. the upper layer comprises two parallel symmetric metal (Ag) plates isolated by 50nm wide gap and upper clad-with EO polymer to form an (MDM plasmonic waveguide) as shown in the attached file
To guarantee a strong coupling between two waveguides, the effective refractive index of the photonic and plasmonic mode should be close. After coupling between photonic and plasmonic modes, The two Eigen modes(quasi-even and quasi-odd) are formed in the coupler
the interference pattern is induced by beating between the quasi-even and quasi-odd mode , and at the coupling length , a nearly complete power transfer from silicon waveguide to plasmonic waveguide

First, I have made a 2D mode analysis (by comsol 4.3b) and received an effective refractive index for photonic mode, plasmonic mode, quasi-even , and quasi-odd mode . I obtain the real part of refractive index for photonic mode and plasmonic mode are 2.1131 and 2.1134 , respectively. this is done by using perfect match layer

when I design 3D coupler (using comsol version 4.3b) using electromagnetic wave beam envelope and boundary mode analysis study . the power is transfer from silicon waveguide to plasmonic (i.e. confined in polymer ) but not completely. what is the problem ? is the perfect match layer (pml)is necessary for 3D boundary mode analysis, becaue in 3D I didn't use pml condition
I excite the 3D design by numerical port , is this right? what is the type of numerical port TE or TM mode

i.e I have added two port , numerical port ,(on silicon layers) I have also created two boundary analyses, one for each port , I search mode around 3.48 silicon, when I compute boundary mode analysis 1, I received 2 modes which Is not same as the photonic mode (in 2D mode analysis)
when I compute the study(boundary mode analysis 1, 2 and frequency domain)and choose power flow time average y component , the problem is (only part of power is transferred from silicon to plasmonic waveguide)

Is the problem in the boundary conditions and PML?? if I must use what is the thickness of pml?
is the physics and study is suitable for this case
Is the problem in mesh???? because I use the default Fine mesh

The other problem when I apply the same steps (3D coupler) above but in comsol version 5, the design is not work (no any power is transferred , no solution) and appear problem
(Failed to find a solution for the initial parameter. The relative error (3.5e+005) is greater than the relative tolerance, returned solution is not converged)
what is the origin of the problem , I attached my work built in comsol version 5 below

Thank you
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