Feasibility of a solely acoustic-wave-driven light amplifier

In Brillouin and Raman lasers, light is amplified by an input pump light through the excited acoustic and molecular oscillations in a medium. However, can medium oscillations alone amplify light in a realistic photonic circuit? Here, we demonstrate that modulating an optical resonator by a traveling wave having the frequency and phase velocity much smaller than the frequency and phase velocity of light can result in dramatically large light amplification accompanied by conversion to multiple comb lines within a relatively small frequency band. Our calculations show that the proposed light amplifier can be realized in a lithium niobate racetrack resonator with millimeter-scale perimeter modulated by a surface acoustic wave with a surprisingly small amplitude and with the propagation constant satisfying the Brillouin phase matching condition.