A device for coupling an input signal to an output signal includes a metal transmission line; an ultra-small resonant receiver structure operatively connected to an end of the transmission line constructed and adapted receive the input signal and to cause at least part of the input signal to be passed along the transmission line in the form of plasmons; an ultra-small resonant transmitter structure operatively connected to another end of the transmission line and constructed and adapted to receive at least some of the plasmons corresponding to the input signal on the transmission line and to transmit the received signal as an output signal; a source of charged particles constructed and adapted to deliver a beam of charged particles along a path adjacent the ultra-small resonant receiver structure, wherein the input signal is encoded in the beam of charged particles; and a detector mechanism constructed and adapted to detect the output signal from the ultra-small resonant transmitter structure and to provide a signal representative of the output signal to another circuit. The receiver and/or transmitter structures may be formed on, in or adjacent to the transmission line.