Abstract
Stimulated Brillouin scattering drives a coherent interaction between optical signals and acoustic phonons and can be used for storing optical information in acoustic waves. An important consideration arises when multiple optical frequencies are simultaneously employed in the Brillouin process: in this case, the acoustic phonons that are addressed by each optical wavelength can be separated by frequencies far smaller than the acoustic phonon linewidth, potentially leading to cross talk between the optical modes. Here we extend the concept of Brillouin-based light storage to multiple wavelength channels. We experimentally and theoretically show that the accumulated phase mismatch over the length of the spatially extended phonons allows each optical wavelength channel to address a distinct phonon mode, ensuring negligible cross talk and preserving the coherence, even if the phonons overlap in frequency. This phase-mismatch for broad-bandwidth pulses has far-reaching implications allowing dense wavelength multiplexing in Brillouin-based light storage, multifrequency Brillouin sensing and lasing, parallel microwave processing, and quantum photon-phonon interactions.
Highlights
Coherent interactions between the optical and the acoustic domain enable breakthrough functionalities in fields such as light storage,1–3 nonreciprocal systems,4–6 generating macroscopic quantum states,7,8 and microwave photonics,9–11 with a number of recent developments in integrated photonic platforms.12–14 Within this broader field, interactions between optical modes and traveling acoustic waves via stimulated Brillouin scattering (SBS) are of particular interest because coupling occurs in the absence of a cavity; the optical field can couple to a continuum of phonon modes rather than being limited to a discrete set of acoustic waves
An important consideration arises when multiple optical frequencies are simultaneously employed in the Brillouin process: in this case, the acoustic phonons that are addressed by each optical wavelength can be separated by frequencies far smaller than the acoustic phonon linewidth, potentially leading to cross talk between the optical modes
We experimentally and theoretically show that the accumulated phase mismatch over the length of the spatially extended phonons allows each optical wavelength channel to address a distinct phonon mode, ensuring negligible cross talk and preserving the coherence, even if the phonons overlap in frequency
Summary
Coherent interactions between the optical and the acoustic domain enable breakthrough functionalities in fields such as light storage, nonreciprocal systems, generating macroscopic quantum states, and microwave photonics, with a number of recent developments in integrated photonic platforms. Within this broader field, interactions between optical modes and traveling acoustic waves via stimulated Brillouin scattering (SBS) are of particular interest because coupling occurs in the absence of a cavity; the optical field can couple to a continuum of phonon modes rather than being limited to a discrete set of acoustic waves. It is known from continuous-wave (CW) studies of multiwavelength optical pumps on Brillouin processes that the three-wave interaction between the optical pump wave, the Stokes wave, and the acoustic wave prevents coupling to additional optical waves that are phasemismatched How these phase and frequency effects carry across to the more complicated situation of optical information storage, in which short pulses at multiple wavelengths are stored coherently in the acoustic domain, is the central question that we seek to address here. We demonstrate how optical pulses at different optical wavelengths can be simultaneously coherently stored in distinct spatially and temporarily overlapping traveling acoustic waves with negligible cross talk. This work conclusively demonstrates that the Brillouin storage involves distinct phonons, notwithstanding their overlap in both the frequency and spatial domains
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