The theory of twisted transverse-wave couplers

The coupled-mode theory of a class of transverse-wave couplers in which the plane of polarization of the electric field rotates along the length of the coupler is described. The synchronism conditions between the circuit wave and the beam that lead to strong interaction with one or more of the transverse beam waves are given and the case of equal interaction with the two cyclotron waves is discussed in detail. It is observed that any two transverse waves of opposite polarization can be excited equally in a twisted coupler, or that coupling to one of two waves with the same phase velocity but opposite polarizations can be achieved.