Can anyone point me to an online resource which gives details - and applications - as to when one should model an optical field using TE and TM modes, and when it's OK to use TEM modes. Cheers. edit: should've stuck this in the normal physics forum... mods please move... More specifics - TE and TM modes can exist in a bounded waveguide, TEM modes can't - however, they can exist in cables... but isn't the latter bounded ?!?!?