Photonic memory is an important building block for all-optical information processing. We experimentally demonstrate storage of quadrature phase-encoded data at ambient and cryogenic temperatures and show all-optical, fully-tunable control of the retrieved optical phase.
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.
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.
With the recent developments in photonic computing platforms, the need of novel optical memories becomes increasingly important. Optoacoustic memories have shown great potential due to their quick access time, coherent nature, and broad bandwidth. These continuously tunable memories can be controlled entirely optically, but so far their intrinsic storage time is limited by the acoustic life time to approximately 10 ns. In this work, we experimentally demonstrate a cryogenic optoacoustic memory with an intrinsic storage time beyond 135 ns.
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 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.