High-efficiency Ka-band frequency multiplier based on the nonlinear kinetic inductance in a superconducting microstrip

Abstract

Local oscillator sources have become a major technological deficit approaching the terahertz frequencies. For applications, where a narrow linewidth is necessary, such as coherent remote sensing, the best solution to signal generation is frequency multiplication, where phase locking can be easily achieved using the fundamental source. We present an alternative to existing frequency multiplier technologies for cryogenic applications. The device is a superconducting waveguide that has kinetic inductance dependent on the rf current through the device. The nonlinear kinetic inductance is anomalous to a nonlinear optical medium, where the Kerr effect causes 3- or 4-wave mixing, as demonstrated in microwave parametric amplifiers utilizing the same nonlinear effect. In 4-wave mixing, three photons at the fundamental frequency are mixed to generate a single photon at the third harmonic. Dispersion engineering is used to achieve wideband phase matching and phase out harmonics higher than the third. The device length is designed to be the point where most photons are up-converted to the third harmonic. Simulations of these devices lead to expected efficiencies as high as 90%. We report results from a NbTiN frequency multiplier from 34.2 to 104 GHz with efficiency better than 50%.