Question related to Optical Waveguides and power

[nordmoon]

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.

 

[chrisbaird]

The power you want is the optical radiant power, not the electrical power. The Poynting vector is the radiant power density and is equal to the cross product of the electric field vector E and the magnetic field vector H at each point in space. If the computational codes present the fields without the time dependence already factored out, you will need to take the time-average of the Poynting vector to get the average energy flux. To get the total power, integrate the time-average Poynting vector over the cross-sectional area of interest (e.g. the output face of the waveguide).

 

[nordmoon]

You are correct, thank you. I forgot about the Poynting vector.