Optical bistability in sideband output modes induced by a squeezed vacuum

We consider $N$ two-level atoms in a ring cavity interacting with a broadband squeezed vacuum centered at frequency ${\ensuremath{\omega}}_{s}$ and an input monochromatic driving field at frequency $\ensuremath{\omega}$. We show that, besides the central mode (at $\ensuremath{\omega}$), an infinity of sideband modes are produced at the output, with frequencies shifted from $\ensuremath{\omega}$ by multiples of $2(\ensuremath{\omega}\ensuremath{-}{\ensuremath{\omega}}_{s})$. We analyze the optical bistability of the two nearest sideband modes, red shifted and blue shifted.