  Kinetic inductance in thin film superconductors has been used as the basis
for low-temperature, low-noise photon detectors. In particular thin films such
as NbTiN, TiN, NbN, the kinetic inductance effect is strongly non-linear in the
applied current, which can be utilized to realize novel devices. We present
results from transmission lines made with these materials, where DC (current)
control is used to modulate the phase velocity thereby enabling an on-chip
spectrometer. The utility of such compact spectrometers are discussed, along
with their natural connection with parametric amplifiers.
