I am doing a 2D COMSOL mode analysis of an optical waveguide. The mode analysis shows you the electric/magnetic field and you want to find out the power of the guided mode. How could I do this? Power is P = I*V or dE/dt with units of Joules per second. In the FEM simulation I have given the wavelength, the dimensions and geometry of my waveguide. I know nothing about the current or voltage... I am missing something here? Is power the same as electric potential energy? What is the difference? My simulations give me the refractive index for each mode solutions and plots of the electric or magnetic fields. Shouldn't I just be able to integrate the area of interest? Not sure if that would give the power.