Abstract
Acoustic waves can serve as memory for optical information; however, propagating acoustic phonons in the gigahertz (GHz) regime decay on the nanosecond time scale. Usually this is dominated by intrinsic acoustic loss due to inelastic scattering of the acoustic waves and thermal phonons. Here we show a way to counteract the intrinsic acoustic decay of the phonons in a waveguide by resonantly reinforcing the acoustic wave via synchronized optical pulses. We experimentally demonstrate coherent on-chip storage in amplitude and phase up to 40 ns, 4 times the intrinsic acoustic lifetime in the waveguide. Through theoretical considerations, we anticipate that this concept allows for storage times up to microseconds within realistic experimental limitations while maintaining a GHz bandwidth of the optical signal.
Highlights
We theoretically explore the limits of the scheme and demonstrate that, within practical limits, even storage times up to microseconds are within reach while maintaining a broad GHz bandwidth of the stored optical pulses
As a first experimental proof, we show that the efficiency of the Brillouin-based storage increases when the acoustic wave is refreshed (Fig. 3)
We demonstrated a way to compensate for the intrinsic acoustic decay of a coherent acoustic phonon in a chip-integrated waveguide
Summary
Coupling optical and mechanical waves in cavities, waveguides, and nanostructures offer great potential for optical signal processing [1,2,3,4,5,6,7,8], especially for delay lines and light storage [9,10,11,12,13,14,15,16,17,18,19]. It was shown recently that one can use these acoustic phonons to store and delay optical signals [9,17,19]. The optical information is resonantly transferred to a coherent acoustic phonon and is transferred back to the optical domain by a delayed optical retrieval pulse completely preserving the phase and amplitude [17] and the wavelength of the signal [19]. Propagating high-frequency acoustic phonons decay exponentially with a lifetime of a few nanoseconds determined by the material properties at room temperature. This inherent decay is due to the damping of the acoustic waves while propagating through the material. The optical information stored in the acoustic waves is lost, and a way of preserving the coherent acoustic vibration is needed
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