# TE and TM modes vs polarization

I have often seen people informally (and sometimes formally) refer to TE and TM modes interchangeably with polarization. I don't see how these modes are related to polarization.

Here is what I think is right:

If one has a TE mode in a simple rectangular metal waveguide, the component of the electric field in the direction of propagation is zero. This is not true for the TM mode, which can have a non-zero component along the direction of propagation. Let us consider that the electric field is horizontally polarized. That is, the mode has a non-zero electric field along the x-axis and a zero field along the y-axis and z-axis.

Now, if we rotate the polarization of this mode by 90 degrees, the electric field is non-zero along the y-axis but zero along the x-axis and z-axis. The magnetic field can now have non-zero components along the x-axis and z-axis but zero along the y-axis.

In this case, the mode is still TE, but just polarized vertically instead of horizontally.

However, this is not what is found in multiple answers on this Researchgate page.

One of the answers from that page is:

TE and TM are used to describe polarization relative to a device (modes in a waveguide, waves incident onto a surface, etc.), while vertical and horizontal describe polarization relative to the ground.

That answer doesn't make much sense to me because it doesn't appear to be referring to which field (electric or magnetic) has a non-zero component along the direction of propagation.

Tl;Dr: how and why are TE and TM modes related to the polarization of light in a waveguide?

• Simply put, not everybody who answers questions on Researchgate knows what they are talking about. The same is true here, but at least we have the voting mechanism to help you work out which answers are and aren't sensible. Oct 20, 2022 at 4:10