Discussion Forum

Hi,

I am trying to simulate a 2D MZM with two MMI at two sides and waveguide at the middle. It is derived from the MZM example for the wave optics module. We don't have the wave optics module. So I used the RF module to simulate it.

It worked pretty well before I applied non-zero electric potential. Then I observed standing wave like waveform as the first figure shown.

I realized that there will be a lot of radiation at the output MMI which may not be able to be absorbed by the scattering boundary condition as the radiation may not incident normally to the boundary. Therefore, I added a PML in addition to the scattering boundary condition.

After I did that, the simulation gave an error as follow:

Undefined variable.
- Variable: comp1.es.Ey
- Geometry: geom1
- Domain: 1
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.emw.epsilonrzz@VDN$y
- Defined as: (((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN)))
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.emw.k@VDN$y
- Defined as: (((((((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murzz)+((comp1.emw.muryy*((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN)))))+(((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murxx)))*0.33333333333333331483)*((((((comp1.emw.epsilonrxx*comp1.emw.murxx)+(comp1.emw.muryy*comp1.emw.epsilonryy))+(comp1.emw.epsilonrzz*comp1.emw.murzz))/3)^(-0.5))*0.5))*comp1.emw.k0)
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.pml1.coordy@VDN$y
- Defined as: ((((((((((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murzz)+((comp1.emw.muryy*((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN)))))+(((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murxx)))*0.33333333333333331483)*((((((comp1.emw.epsilonrxx*comp1.emw.murxx)+(comp1.emw.muryy*comp1.emw.epsilonryy))+(comp1.emw.epsilonrzz*comp1.emw.murzz))/3)^(-0.5))*0.5))*comp1.emw.k0))*((-((1-i)*(((-6666666.6666666669771)*(((x+3.4694468903532394968e-23)*1.1564822967844132682e-16)-y))*pi)))/(comp1.emw.k^2)))+(((6666666.6666666669771*pi)*(1-i))*(1/comp1.emw.k)))
Failed to evaluate variable.
- Variable: comp1.pml1.invT22
- Defined as: d(comp1.pml1.coordy,y)
Failed to evaluate variable.
- Variable: comp1.pml1.detInvT
- Defined as: (((comp1.pml1.invT22*comp1.pml1.invT11)-(comp1.pml1.invT21*comp1.pml1.invT12))*comp1.pml1.invT33)
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.emw.curltestdepEx@VDN${test@4}
- Defined as: ((1/comp1.pml1.detInvT)*(-comp1.pml1.invT21))
Failed to evaluate expression.
- Expression: d((-mu0_const*(-comp1.emw.dHdtx*comp1.emw.curltestdepEx-comp1.emw.dHdty*comp1.emw.curltestdepEy+comp1.emw.iomega*comp1.emw.Jz*comp1.emw.testdepEz)*comp1.pml1.detInvT)*(dvol),{test@4})

It worked until the stationary step (no error comes out), but not any more. Plz help me to figure out the problem and if possible let me know why I have weird waveform as shown in first few figures. Is it really due to the incomplete absorption of the radiated wave by the SBC?

I attached the normE plot of the standing-wave like results and the model file of MZM_SBC and the model with PML added MZM_PML1.

Thank you very much.