  The nonlinear response associated with the current dependence of the
superconducting kinetic inductance was studied in capacitively shunted NbTiN
microstrip transmission lines. It was found that the inductance per unit length
of one microstrip line could be changed by up to 20% by applying a DC current,
corresponding to a single pass time delay of 0.7 ns. To investigate nonlinear
dissipation, Bragg reflectors were placed on either end of a section of this
type of transmission line, creating resonances over a range of frequencies.
From the change in the resonance linewidth and amplitude with DC current, the
ratio of the reactive to the dissipative response of the line was found to be
788. The low dissipation makes these transmission lines suitable for a number
of applications that are microwave and millimeter-wave band analogues of
nonlinear optical processes. As an example, by applying a millimeter-wave pump
tone, very wide band parametric amplification was observed between about 3 and
34 GHz. Use as a current variable delay line for an on-chip millimeter-wave
Fourier transform spectrometer is also considered.
