Effective index and singular matrix error

Hi everyone,

I am trying to analyze a silicon waveguide by COMSOL 3.5 using RF Module - Perpendicular waves, and I need to find the effective index for a set of wavelength. I have had no problems to run my simulation for just one value of wavelength, for this I have chosen "Eigenvalue" at "Solver parametrers" window and I just set the fields "Desired number of effective mode indices" and "Search for effective mode indices around" and it gives the appropriate result. On the other hand when I try to run a simulation for several wavelentgh values I have chosen "parametric" at "Solver parametrers" window and set the "Parameter name" as "lambda0_rfweh", which is the name used by COMSOL, and I define the set of wavelentghs at "Parameter values" as: "First value: 1500E-9", "Last Value: 1560E-9" and "Number of values: 100". When I try to run this simulation I get the error "7111 Singular matrix ". Could someone please help me set up this simulation properly to find the values ​​of effective index for a set of wavelengths?

Thanks!

João