I make simulations in a material KYW the structure looks like as shown below
where the upper part is air with refractive index 1, red part KYW with refractive index= 2,
the green/yellow part an adhesive with refractive index of 1.56 and the lower green part SiO2
with refractive index of 1.44.
I do my simulations at a wavelength of 1.55 micrometer and obtain the results as shown in
the figure. There are negative losses which I do not expect to obtain because all the materials
My simulation region is 12 micrometer wide and 8 micrometer high all with PML boundary conditions.
The gridsize is 20 x 20 nanometer
Can someone give an explanation why the losses are negative?