  System with strong photon-phonon interaction and optomechanical instability
are perspective for generation of coherent phonons and photons. Typically,
above the threshold of optomechanical instability, the photon intensity
increases linearly with pumping. We demonstrate that in such systems, it is
possible to achieve hard mode of excitation when jump increase in the photon
intensity takes place. We derive the analytical expression determining
conditions for such a jump increase. We demonstrate that the hard excitation
mode in system with optomechanical instability arises due to an additional
phase condition for the existence of a nonzero solution. The discovered hard
excitation mode paves the way for creation highly sensitive sensors and optical
transistors.
