slab-waveguide simulation / scattering losses

Hello,

I'm attempting to simulate a simple slab waveguide (see attached). The waveguide has a core of n=1.5 surrounded by air (n=1) above and below. This design is surrounded by PML rectangles.
The boundary conditions and the size of the core are selected to be such that the electric field imposed on the three left boundaries (inside, to the right the PML, top to bottom) is a mode supported by the waveguide:

exp(-p0*y)
exp(-p0*d)*cos(h0*y)/cos(h0*d)
exp(p0*y)

The physics is based on the RF Module / photonic crystal model library in Comsol 3.5a.

I would like to know the core power input (left) and output (right). To this end, I have two questions:

1. I would like to take the core (middle subdomain), integrate the y-values and get a vector of the average power in each x value of the core. According to this vector I'd like to generate a graph of the decline of power from input to output as a function of propagation length x. Is this possible in Comsol?

2. I select the core input, and from Post Processing I choose "Power outflow, time average" (nPoav_rfwe), which seems a reasonable choice, but the results don't make sense to me (the input power -6.793381e-11 [W/m] is lower than the output -3.18875e-10 [W/m]; also, what do the signs mean? how can I simulate "time average" when the simulation is not time-dependent?). I would appreciate suggestions on how to measure the input and output power.

I'm attaching the model if anyone's interested.

Thanks in advance!