The polarization of the photonic field can be written as a linear combination of the transverse electric (TE) polarization, êk,TE , and the transverse magnetic (TM) polarization, êk,TM , in relation to a given interface and propagation direction. The TE mode's polarization, êk,TE , is defined as being perpendicular to the propagation direction and parallel to the interface. The TM mode's polarization, êk,TM , is defined as being perpendicular to both the propagation direction and the TE polarization. For a given polarization, êk , the transverse electric field is along êk and the magnetic field is along the k×ê k direction. For example, for the TM mode, the transverse electric field polarization is along êk,TE and the transverse magnetic field polarization is along -ê k,TM .