Two States of Polarization of EM Waves

[inticore]

I am studying about the cavity radiation inside a metallic cube. In the textbook it states that there are two independent waves corresponding to the two possible states of polarization of electromagnetic waves. What does it mean by this? (My current assumption is the phase change of the waves)

It's stated in the last sentence before the equation (1-11). The textbook is "Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles" by Eisberg R. and Resnick R. if it helps. I'm don't understand on the need to multiply by a factor of 2.

 

[tech99]

If you imagine communication via a square waveguide, it is possible to use, say, either vertically polarised waves or horizontally polarised waves. These have a separate existence and we can send different messages on either one and they can also have different frequencies. If we put metal plates on either end of the square waveguide, we have a cavity resonator, and two polarisations can still exist inside it. But now, due to the geometry, only certain narrow frequency bands can be supported.
Although I said horizontal and vertical, this is a simplification, as a very large number of modes can exist, but each one has its orthogonal, or cross polarised, partner. Each polarisation contains half the total energy in the cavity.

 

[inticore]

If you imagine communication via a square waveguide, it is possible to use, say, either vertically polarised waves or horizontally polarised waves. These have a separate existence and we can send different messages on either one and they can also have different frequencies. If we put metal plates on either end of the square waveguide, we have a cavity resonator, and two polarisations can still exist inside it. But now, due to the geometry, only certain narrow frequency bands can be supported.
Although I said horizontal and vertical, this is a simplification, as a very large number of modes can exist, but each one has its orthogonal, or cross polarised, partner. Each polarisation contains half the total energy in the cavity.

So, what I understand is that the cavity resonator limits the polarization to 2 states and also narrows the allowed frequencies. This explains so much, thanks.