Storing Optical Information as a Mechanical Excitation in a Silica Optomechanical Resonator

We report the experimental demonstration of storing optical information as a mechanical excitation in a silica optomechanical resonator. We use writing and readout laser pulses tuned to one mechanical frequency below an optical cavity resonance to control the coupling between the mechanical displacement and the optical field at the cavity resonance. The writing pulse maps a signal pulse at the cavity resonance to a mechanical excitation. The readout pulse later converts the mechanical excitation back to an optical pulse. The storage lifetime is determined by the relatively long damping time of the mechanical excitation.

Figure 1

(a) Schematic of an optomechanical resonator. (b) Spectral position for the writing, readout, and signal pulses. (c) The intensity of intracavity signal and retrieved pulses (solid red line), along with the intensity of the stored mechanical oscillation (dotted black line), as a function of time, illustrating the optomechanical process of light storage and retrieval.

Figure 2

(a) The power of the heterodyne-detected signal and retrieved pulses emitted from the resonator as a function of time. The solid curve serves as a guide to the eye. The inset illustrates free-space evanescent excitation of a WGM and the timing of the writing and readout pulses used for the experiment. (b) Retrieved pulse energy as a function of the delay between the readout ($3\mu \mathrm{s}$ in duration) and writing pulses. An exponential fit shown as the red dotted line yields a storage lifetime of $3.5\mu \mathrm{s}$. (c) The temporal profile of the retrieved pulse generated by a readout pulse with duration of 0.3, 0.6, $1.4\mu \mathrm{s}$ (from bottom to top), under otherwise identical conditions as those for (a).

Figure 3

(a) Retrieved pulse energy as a function of the relative readout intensity. (b) Retrieved pulse energy (normalized to that at zero detuning) as a function of ${\omega }_s-{\omega }_l-{\omega }_m$ and with a relative readout intensity of 1 (blue squares) and 0.45 (black circles). The red dotted lines in (a) and (b) show the theoretical calculations with all parameters taken from the experiment. (c) Theoretically calculated temporal profile of the signal and retrieved pulses, along with the intensity of the stored mechanical oscillation (dotted line), with all parameters taken from the experiment in Fig. 2a. The inset shows the calculated spatial displacement pattern of the (1, 2) mechanical mode.