Electromagnetic diode action in an asymmetric side-coupled cavity-resonator system

A novel compact electromagnetic diode based on Fano resonance is reported, realized by combining a ­defective photonic crystal with a varactor-loaded split ring resonator. One-way response is achieved in a microwave waveguide system, attributed to the sharp asymmetric Fano lineshape, the strong nonlinearity enhancement, and the pronounced nonreciprocal field localization. A low threshold intensity of −1.6 dBm, a high transmission contrast up to 17.1 dB, and a maximal transmission over −16 dB are achieved within a subwavelength volume. Compared with conventional electromagnetic diode designs based on ­defective photonic crystals, the presence of interaction between cavity and resonator provides more flexibility in tuning the transmission properties. The findings may be beneficial for designing nonreciprocal integrated photonic devices in practical application.