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.
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.
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.
Optical and acoustic waves can interact over the nonlinear effect of stimulated Brillouin scattering (SBS), which is a coherent process. By using traveling acoustic waves, we recently showed proof-of-principle experiments of Brillouin-based light storage. The particularity of Brillouin-based light storage is the strict phase-matching condition. This allows for different features: simultaneous storage at multiple wavelengths, cascaded storage at different spatial positions, and nonreciprocal storage with a GHz bandwidth. However, the delay time of this technique has so far been limited to the acoustic lifetime of about 10 ns. In this talk, I will discuss our recent results on coherent photon-phonon interaction. One focus will be on a proof-of-principle experiments on how to reinforce acoustic phonons. This enables us to overcome the obstacle of the limited acoustic lifetime by optically reinforcing the acoustic wave.
The importance of optical signal processing techniques is growing rapidly in recent years due to the exponentially increasing demand for bandwidth, capacity and power efficiency in communications and computing. However, due to their bosonic nature photons do not interact with each other, unless there is a nonlinear medium mediating the interaction. One of the strongest nonlinear effects is the interaction of light waves, photons, with sound-waves, acoustic phonons, which is known as stimulated Brillouin scattering (SBS). This thesis experimentally investigates SBS in photonic chips. It is shown in this thesis that the fundamental interaction strength between light and sound waves can be tailored by using one-dimensional photonic bandgap structures, completely suppressing the effect or alternatively enhancing the interaction to form phase-locked Brillouin frequency combs. It was shown furthermore that efficiently generating SBS on-chip enables the generation of stable RF signals that are widely tunable in frequency. Finally, it is shown in this thesis that SBS enables the storage of light signals on a chip, one of the holy grails of all-optical signal processing. Delaying optical signals is of key importance in optical networks to enable synchronization, buffering, and rerouting. SBS enables large delays by resonantly transferring an optical signal to an acoustic wave, that travels five orders of magnitude slower and retrieving it after a certain storage time. It is demonstrated in this thesis that a Brillouin-based memory (BBM) technique allows storing amplitude and phase of optical data pulses and operate at multiple wavelengths with minimal cross-talk. Replenishing of the acoustic wave to overcome storage time limitations imposed by the lifetime of the acoustic wave as well as non-reciprocal light storage is also shown.
High Resolution Image Download MS PowerPoint Slide In recent years, remarkable advances in photonic computing have highlighted the need for photonic memory, particularly high-speed and coherent random-access memory. Addressing the ongoing challenge of implementing photonic memories is required to fully harness the potential of photonic computing. A photonic-phononic memory based on stimulated Brillouin scattering is a possible solution, as it coherently transfers optical information into sound waves at high-speed. Such an optoacoustic memory has shown great potential as it fulfills key requirements for high-performance optical random-access memory due to its coherence, on-chip compatibility, frequency selectivity, and high bandwidth. However, the storage time has so far been limited to a few nanoseconds due to the nanosecond decay of the acoustic wave. In this work, we experimentally enhance the intrinsic storage time of an optoacoustic memory by more than 1 order of magnitude and coherently retrieve optical information after a storage time of 123 ns. This is achieved by employing the optoacoustic memory in a highly nonlinear fiber at 4.2 K, increasing the intrinsic phonon lifetime by a factor of 6. We demonstrate the capability of our scheme by measuring the initial and readout optical data pulses with a direct and double homodyne detection scheme. Finally, we analyze the dynamics of the optoacoustic memory at different cryogenic temperatures in the range of 4.2–20 K and compare the findings to continuous wave measurements. The extended storage time is beneficial not only for photonic computing but also for Brillouin applications that require long phonon lifetimes, such as optoacoustic filters, true-time delay networks, and synthesizers in microwave photonics.
Stimulated Brillouin scattering describes a way to excite coherent acoustic phonons solely by optically forces in integrated waveguides. It was shown recently that one can use these acoustic phonons to store and delay optical signals [1], [2]. The optical information is resonantly transferred to a coherent acoustic phonon and is then transferred back to the optical domain by a delayed optical retrieval pulse. The storage time, however, is so far limited to a few nanoseconds, determined by the lifetime of the acoustic phonon. A delay of several nanoseconds might be enough for delaying some high speed signals, however increasing the delay time beyond the acoustic lifetime would enable new possibilities for phonon-based on-chip optical signal processing.
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.