http://link.springer.com/content/pdf/10.1140%2Fepjb%2Fe2013-31066-8.pdf#
How to control the mixing of two separate frequencies ω1 and ω2 is studied in a nonlinear Josephson-vortex THz photonic crystal in layered superconductors. Due to nonlinearity sum and difference frequencies can be generated, allowing controlled frequency shifting of electromagnetic waves within the THz range of the spectrum which is difficult to reach with current devices. Assuming no feedback from higher harmonics allows the sum and difference amplitudes to be calculated numerically using a perturbative method. We observed a strong resonance amplification of sum and difference mixing harmonics of two basic THz signals for certain ratios of ω1 and ω2. An analytical approach was proposed to understand the physical origin of such amplification.
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