We theoretically and numerically study the efficiency of Brillouin-based opto-acoustic data storage in a photonic waveguide in the presence of thermal noise and laser phase noise. We compare the physics of the noise processes and how they affect different storage techniques, examining both amplitude and phase storage schemes. We investigate the effects of storage time and pulse properties on the quality of the retrieved signal and find that phase storage is less sensitive to thermal noise than amplitude storage.
We theoretically and numerically study the efficiency of Brillouin-based opto-acoustic data storage in a photonic waveguide in the presence of thermal noise and laser phase noise. We compare the physics of the noise processes and how they affect different storage techniques, examining both amplitude and phase storage schemes. We investigate the effects of storage time and pulse properties on the quality of the retrieved signal and find that phase storage is less sensitive to thermal noise than amplitude storage.
We theoretically and numerically study the efficiency of Brillouin-based opto-acoustic data storage in a photonic waveguide in the presence of thermal noise and laser phase noise. We compare the physics of the noise processes and how they affect different storage techniques, examining both amplitude and phase storage schemes. We investigate the effects of storage time and pulse properties on the quality of the retrieved signal and find that phase storage is less sensitive to thermal noise than amplitude storage.
Storing and delaying optical information is of crucial importance for optical communications, signal processing and in the quantum domain. A plethora of techniques for optical storage have been shown which aim to maintain as much as possible the advantages of optics, such as e.g. the coherence, the bandwidth and capacity. In particular the interaction of optical waves with mechanical motion offers a solution to buffer optical information [1-4]. It was shown that one can use acoustic waves to store and delay optical signals coherently via the effect of stimulated Brillouin scattering (SBS) [3,4]. This allows for simultaneous storage at multiple wavelengths [5], cascaded storage at different spatial positions [6], and nonreciprocal storage with a GHz bandwidth [7]. However, the delay time of this technique is so far limited to the acoustic lifetime of about 10 ns.
Photonic memory is an important building block to delay, route, and buffer optical information, for instance, in optical interconnects or for recurrent optical signal processing. Photonic–phononic memory based on stimulated Brillouin–Mandelstam scattering (SBS) has been demonstrated as a coherent optical storage approach with broad bandwidth, frequency selectivity, and intrinsic nonreciprocity. Here, we experimentally demonstrate the storage of quadrature-phase encoded data at room temperature and at cryogenic temperatures. We store and retrieve the 2-bit states {00, 01, 10, 11} encoded as optical pulses with the phases {0,π2,π,3π2}—a quadrature phase shift keying signal. The 2-bit signals are retrieved from the acoustic domain with a global phase rotation of π, which is inherent in the process due to SBS. We also demonstrate full phase control over the retrieved data based on two different handles: by detuning slightly from the SBS resonance or by changing the storage time in the memory scheme, we can cover the full range [0, 2π). At a cryogenic temperature of 3.9 K, we have increased readout efficiency as well as gained access to longer storage times, which results in a detectable signal at 140 ns. All in all, the work sets the cornerstone for optoacoustic memory schemes with phase-encoded data.
In order to deliberately control the flow of optically encoded information, optical storage is an indispensable tool, but it must maintain all the advantages of optics, such as i.e. the coherence, the bandwidth and capacity. An elegant approach to this problem is to coherently transfer the information from optical to acoustic waves via an opto-mechanical nonlinearity, such as stimulated Brillouin scattering (SBS). The basic concept was first demonstrated in highly nonlinear fiber by Zhu et al. [1]. Recently, we experimentally demonstrated the coherence of this memory concept by encoding different amplitude and phase levels in an integrated photonic circuit [2] and the compatibility with wavelength division multiplexing [3]. This concept is based on a straight waveguide without the need of a structural resonance as an opto-mechanical resonator or a photonic crystal cavity. Therefore, the memory operation can be arbitrarily positioned on the photonic chip and can even be repeated and cascaded several times, via external control light pulses.
We experimentally show an optoacoustic memory based on Brillouin scattering with one order of magnitude higher storage time that retrieves amplitude and phase information after 120ns. We increase the intrinsic phonon lifetime of a highly nonlinear fiber by a factor of six by cooling the fiber down to 4.2K. We demonstrate the performance enhancement of optoacoustic memory by measuring the amplitude and phase information of an initial data pulse and its corresponding retrieved readout pulse using direct and double homodyne detection. Furthermore, we present the influence of different cryogenic temperatures between 4.2K and 20K on the optoacoustic memory and compare the results with continuous-wave measurements. In conclusion, our work can not only accelerate photonic computing but also advance other applications of stimulated Brillouin scattering that require long phonon lifetimes, such as optoacoustic filters in microwave photonics. In addition, the presented long-lasting sound wave optoacoustic memory is compatible with active acoustic refreshment technique potentially leading to all-optical coherent memory beyond 1 μs.
Stimulated Brillouin scattering drives a coherent interaction between optical signals and acoustic phonons and this effect 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 crosstalk 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 crosstalk, even if the phonons overlap in frequency. Moreover, we demonstrate that the strict phase matching condition enables the preservation of the coherence of the opto-acoustic transfer at closely spaced multiple acoustic frequencies. This particular phase-mismatch for broad-bandwidth pulses has far-reaching implications allowing dense wavelength multiplexing in Brillouin-based light storage, multi-frequency Brillouin sensing, multi-wavelength Brillouin lasers, parallel microwave processing and quantum photon-phonon interactions.