Optomechanical frequency comb memory.

Typical nano-mechanical oscillator arrays exhibit a mechanical frequency distribution arising from the imprecision in the nanofabrication process, thus hindering their collective dynamics. We tailor the inhomogeneously broadened spectrum of a nano-oscillator ensemble to unravel the collective dynamics of mechanical oscillators in an optomechanical array. We show that by engineering tunable optomechanical interactions, the instantaneous phase matching between the oscillators reveals collective dynamics in the form of a photon-phonon echo excitation without the need for active frequency tuning. Using numerical simulations, we demonstrate that by controlling such collective dynamics, broadband and scalable coherent light storage can be realized. An optomechanical memory of this kind enables information storage over a wide band of wavelengths, including the telecommunications band and, importantly, can be integrated into the silicon photonic networks.