  We propose a scheme of continuous tunable THz emission based on dipolaritons
--- mixtures of strongly interacting cavity photons and direct excitons, where
the latter are coupled to indirect excitons via tunnelling. We investigate the
property of multistability under continuous wave (CW) pumping, and the
stability of the solutions. We establish the conditions of parametric
instability, giving rise to oscillations in density between the direct exciton
and indirect modes under CW pumping. In this way we achieve continuous and
tunable emission in the THz range in a compact single-crystal device. We show
that the emission frequency can be tuned in a certain range by varying an
applied electric field and pumping conditions. Finally, we demonstrate the
dynamic switching between different phases in our system, allowing rapid
control of THz radiation.
