Abstract: Aspects of the present disclosure may address the problem of coupling a radio-frequency (RF) input signal to a light-frequency emitting diode, where the output impedance of the device providing the input signal and the diode input impedance differ. A coupler according to aspects of the present disclosure may be a capacitive coupler that may take the form of parallel concentric coils, which may be comprised of wire or metal plate coils, or parallel plates, connected in series with a variable capacitive element. According to a further aspect of the present disclosure, parallel concentric coils and parallel plates may be arranged in parallel, and the input signal to the coupler may be switched to one or the other. The switching may be automated, based on frequency content or amplitude of the input signal.