Optical Neural Network Architecture for Deep Learning with Temporal Synthetic Dimension

The physical concept of synthetic dimensions has recently been introduced into optics.The fundamental physics and applications are not yet fully understood,and this report explores an approach to optical neural networks using synthetic dimension in time domain,by theoretically proposing to utilize a single resonator network,where the arrival times of optical pulses are interconnected to construct a temporal synthetic dimension.The set of pulses in each roundtrip therefore provides the sites in each layer in the optical neural network,and can be linearly transformed with splitters and delay lines,including the phase modulators,when pulses circulate inside the network.Such linear transformation can be arbitrarily controlled by applied modulation phases,which serve as the building block of the neural network together with a nonlinear component for pulses.We validate the functionality of the proposed optical neural network for the deep learning purpose with examples handwritten digit recognition and optical pulse train distribution classification problems.This proof of principle computational work explores the new concept of developing a photonics-based machine learning in a single ring network using synthetic dimensions,which allows flexibility and easiness of reconfiguration with complex functionality in achieving desired optical tasks.

New Insight into the Development of Oxygen Carrier Materials for Chemical Looping Systems

化学链燃烧(CLC)和化学链重整(CLR)是通过循环氧化还原反应,清洁高效地将烃类转化为动力、燃料和化学品的创新技术。金属氧化物材料在化学链氧化还原过程中起着至关重要的作用。在还原过程中,氧载体为烃类的转化和产物合成提供所需的氧离子量。在氧化步骤中,耗尽的金属氧化物氧载体从空气中补充分子氧,同时释放热量。近年来,用于各种化学链应用的氧载体材料已经取得了较大进展。在这些金属氧化物材料中,铁基氧载体由于其高携氧能力、显著的成本效益,以及化学链反应在实际应用方面的多功能性而具有吸引力。它们的反应性也可以通过结构设计和改性进一步得到增强。本文综述了氧载体材料的发展及其在这些材料上的烃类转化机制的最新进展。这些进展将有助于氧载体材料的开发,以实现更有效的化学链技术应用。

Inverse-designed silicon carbide quantum and nonlinear photonics

Inverse design has revolutionized the field of photonics,enabling automated development of complex structures and geometries with unique functionalities unmatched by classical design.However,the use of inverse design in nonlinear photonics has been limited.In this work,we demonstrate quantum and classical nonlinear light generation in silicon carbide nanophotonic inverse-designed Fabry-Pérot cavities.We achieve ultra-low reflector losses while targeting a pre-specified anomalous dispersion to reach optical parametric oscillation.By controlling dispersion through inverse design,we target a second-order phase-matching condition to realize second-and third-order nonlinear light generation in our devices,thereby extending stimulated parametric processes into the visible spectrum.This first realization of computational optimization for nonlinear light generation highlights the power of inverse design for nonlinear optics,in particular when combined with highly nonlinear materials such as silicon carbide.

Multi-dimensional band structure spectroscopy in the synthetic frequency dimension

The concept of synthetic dimensions in photonics provides a versatile platform in exploring multi-dimensional physics.Many of these physics are characterized by band structures in more than one dimensions.Existing efforts on band structure measurements in the photonic synthetic frequency dimension however are limited to either onedimensional Brillouin zones or one-dimensional subsets of multi-dimensional Billouin zones.Here we theoretically propose and experimentally demonstrate a method to fully measure multi-dimensional band structures in the synthetic frequency dimension.We use a single photonic resonator under dynamical modulation to create a multidimensional synthetic frequency lattice.We show that the band structure of such a lattice over the entire multidimensional Brillouin zone can be measured by introducing a gauge potential into the lattice Hamiltonian.Using this method,we perform experimental measurements of two-dimensional band structures of a Hermitian and a non-Hermitian Hamiltonian.The measurements reveal some of the general properties of point-gap topology of the non-Hermitian Hamiltonian in more than one dimensions.Our results demonstrate experimental capabilities to fully characterize high-dimensional physical phenomena in the photonic synthetic frequency dimension.

Self-configuring universal linear optical component[Invited]

We show how to design an optical device that can perform any linear function or coupling between inputs and outputs.This design method is progressive,requiring no global optimization.We also show how the device can configure itself progressively,avoiding design calculations and allowing the device to stabilize itself against drifts in component properties and to continually adjust itself to changing conditions.This self-configuration operates by training with the desired pairs of orthogonal input and output functions,using sets of detectors and local feedback loops to set individual optical elements within the device,with no global feedback or multiparameter optimization required.Simple mappings,such as spatial mode conversions and polarization control,can be implemented using standard planar integrated optics.In the spirit of a universal machine,we show that other linear operations,including frequency and time mappings,as well as nonreciprocal operation,are possible in principle,even if very challenging in practice,thus proving there is at least one constructive design for any conceivable linear optical component;such a universal device can also be self-configuring.This approach is general for linear waves,and could be applied to microwaves,acoustics,and quantum mechanical superpositions.

Unscrambling light-automatically undoing strong mixing between modes

Propagation of light beams through scattering or multimode systems may lead to the randomization of the spatial coherence of the light.Although information is not lost,its recovery requires a coherent interferometric reconstruction of the original signals,which have been scrambled into the modes of the scattering system.Here we show that we can automatically unscramble optical beams that have been arbitrarily mixed in a multimode waveguide,undoing the scattering and mixing between the spatial modes through a mesh of silicon photonics tuneable beam splitters.Transparent light detectors integrated in a photonic chip are used to directly monitor the evolution of each mode along the mesh,allowing sequential tuning and adaptive individual feedback control of each beam splitter.The entire mesh self-configures automatically through a progressive tuning algorithm and resets itself after significantly perturbing the mixing,without turning off the beams.We demonstrate information recovery by the simultaneous unscrambling,sorting and tracking of four mixed modes,with residual cross-talk of−20 dB between the beams.Circuit partitioning assisted by transparent detectors enables scalability to meshes with a higher port count and to a higher number of modes without a proportionate increase in the control complexity.The principle of self-configuring and self-resetting in optical systems should be applicable in a wide range of optical applications.

Higher-order topological insulators in synthetic dimensions

Conventional topological insulators support boundary states with dimension one lower than that of the bulk system that hosts them,and these states are topologically protected due to quantized bulk dipole moments.Recently,higherorder topological insulators have been proposed as a way of realizing topological states with dimensions two or more lower than that of the bulk due to the quantization of bulk quadrupole or octupole moments.However,all these proposals as well as experimental realizations have been restricted to real-space dimensions.Here,we construct photonic higher-order topological insulators(PHOTIs)in synthetic dimensions.We show the emergence of a quadrupole PHOTI supporting topologically protected corner modes in an array of modulated photonic molecules with a synthetic frequency dimension,where each photonic molecule comprises two coupled rings.By changing the phase difference of the modulation between adjacent coupled photonic molecules,we predict a dynamical topological phase transition in the PHOTI.Furthermore,we show that the concept of synthetic dimensions can be exploited to realize even higher-order multipole moments such as a fourth-order hexadecapole(16-pole)insulator supporting 0D corner modes in a 4D hypercubic synthetic lattice that cannot be realized in real-space lattices.

Thermodynamic limits for simultaneous energy harvesting from the hot sun and cold outer space

The sun and outer space are two of the most important fundamental thermodynamic resources for renewable energy harvesting.A significant amount of work has focused on understanding the fundamental limit of energy harvesting from the sun.More recently,there have been several theoretical analyses of the fundamental limit of energy harvesting from outer space.However,far less is understood about the fundamental limits of simultaneous energy harvesting from both the sun and outer space.Here,we consider and introduce various schemes that are capable of simultaneous energy harvesting and elucidate the fundamental thermodynamic limits of these schemes.We show that the theoretical limits can far exceed the previously established limit associated with utilizing only one thermodynamic resource.Our results highlight the significant potential of simultaneous energy harvesting and indicate new fundamental opportunities for improving the efficiency of energy harvesting systems.

Multidimensional synthetic chiral-tube lattices via nonlinear frequency conversion

Geometrical dimensionality plays a fundamentally important role in the topological effects arising in discrete lattices.Although direct experiments are limited by three spatial dimensions,the research topic of synthetic dimensions implemented by the frequency degree of freedom in photonics is rapidly advancing.The manipulation of light in these artificial lattices is typically realized through electro-optic modulation;yet,their operating bandwidth imposes practical constraints on the range of interactions between different frequency components.Here we propose and experimentally realize all-optical synthetic dimensions involving specially tailored simultaneous short-and long-range interactions between discrete spectral lines mediated by frequency conversion in a nonlinear waveguide.We realize triangular chiral-tube lattices in three-dimensional space and explore their four-dimensional generalization.We implement a synthetic gauge field with nonzero magnetic flux and observe the associated multidimensional dynamics of frequency combs,all within one physical spatial port.We anticipate that our method will provide a new means for the fundamental study of high-dimensional physics and act as an important step towards using topological effects in optical devices operating in the time and frequency domains.

Separating arbitrary free-space beams with an integrated photonic processor

Free-space optics naturally offers multiple-channel communications and sensing exploitable in many applications. The different optical beams will, however, generally be overlapping at the receiver, and, especially with atmospheric turbulence or other scattering or aberrations, the arriving beam shapes may not even be known in advance. We show that such beams can be still separated in the optical domain, and simultaneously detected with negligible cross-talk, even if they share the same wavelength and polarization, and even with unknown arriving beam shapes. The kernel of the adaptive multibeam receiver presented in this work is a programmable integrated photonic processor that is coupled to free-space beams through a two-dimensional array of optical antennas. We demonstrate separation of beam pairs arriving from different directions, with overlapping spatial modes in the same direction, and even with mixing between the beams deliberately added in the path. With the circuit’s optical bandwidth of more than 40 nm, this approach offers an enabling technology for the evolution of FSO from single-beam to multibeam space-division multiplexed systems in a perturbed environment, which has been a game-changing transition in fiber-optic systems.

Coherent self-control of free-space optical beams with integrated silicon photonic meshes

In technologies operating at light wavelengths for wireless communication,sensor networks,positioning,and ranging,a dynamic coherent control and manipulation of light fields is an enabling element for properly generating and correctly receiving free-space optical(FSO)beams even in the presence of unpredictable objects and turbulence in the light path.In this work,we use a programmable mesh of Mach-Zehnder(MZI)interferometers to automatically control the complex field radiated and captured by an array of optical antennas.The implementation of local feedback control loops in each MZI stage,without global multivariable optimization techniques,enables an unlimited scalability.Several functionalities are demonstrated,including the generation of perfectly shaped beams with nonperfect optical antennas,the imaging of a desired field pattern through an obstacle or a diffusive medium,and the identification of an unknown obstacle inserted in the FSO path.Compared to conventional devices used for the manipulation of FSO beams,such as spatial light modulators,our programmable device can self-configure through automated control strategies and can be integrated with other functionalities implemented onto the same photonic chip.

Low-overhead distribution strategy for simulation and optimization of large-area metasurfaces

Fast and accurate electromagnetic simulation of large-area metasurfaces remains a major obstacle in automating their design.In this paper,we propose a metasurface simulation distribution strategy which achieves a linear reduction in the simulation time with the number of compute nodes.Combining this distribution strategy with a GPU-based implementation of the Transition-matrix method,we perform accurate simulations and adjoint sensitivity analysis of large-area metasurfaces.We demonstrate ability to perform a distributed simulation of large-area metasurfaces(over 600λ×600λ),while accurately accounting for scatterer-scatterer interactions significantly beyond the locally periodic approximation.

Thermal photonics with broken symmetries

Nanophotonic engineering provides an effective platform to manipulate thermal emission on-demand,enabling unprecedented heat management superior to conventional bulk materials.Amongst a plethora of nanophotonic structures,symmetries play an important role in controlling radiative heat transfer in both near-field and far-field.In physics,broken symmetries generally increase the degree of freedom in a system,enriching the understanding of physical mechanisms and bringing many exciting opportunities for novel applications.In this review,we discussed the underlying physics and functionalities of nanophotonic structures with broken geometrical symmetries,engineered mode symmetries,and broken reciprocity for the control of thermal emission.We overview a variety of physical phenomena and interesting applications,and provide the outlook for future development.

Creating locally interacting Hamiltonians in the synthetic frequency dimension for photons

The recent emerging field of synthetic dimension in photonics offers a variety of opportunities for manipulating different internal degrees of freedom of photons such as the spectrum of light.While nonlinear optical effects can be incorporated into these photonic systems with synthetic dimensions,these nonlinear effects typically result in long-range interactions along the frequency axis.Thus,it has been difficult to use the synthetic dimension concept to study a large class of Hamiltonians that involves local interactions.Here we show that a Hamiltonian that is locally interacting along the synthetic dimension can be achieved in a dynamically modulated ring resonator incorporatingχ3nonlinearity,provided that the group velocity dispersion of the waveguide forming the ring is specifically designed.As a demonstration we numerically implement a Bose–Hubbard model and explore photon blockade effect in the synthetic frequency space.Our work opens new possibilities for studying fundamental many-body physics in the synthetic space in photonics,with potential applications in optical quantum communication and quantum computation.

Design of a multichannel photonic crystal dielectric laser accelerator

To be useful for most scientific and medical applications,compact particle accelerators will require much higher average current than enabled by current architectures.For this purpose,we propose a photonic crystal architecture for a dielectric laser accelerator,referred to as a multi-input multi-output silicon accelerator(MIMOSA),that enables simultancous acceleration of multiple electron beams,increasing the total electron throughput by at least I order of magnitude.To achieve this,we show that the photonic crystal must support a mode at the I point in reciprocal space,with a normalized frequency equal to the normalized speed of the phase-matched electron.We show that the figure of merit of the MIMOSA can be inferred from the eigenmodes of the corresponding infinitely periodic structure,which provides a powerful approach to design such devices.Additionally,we extend the MIMOSA architecture to electron deflectors and other clectron manipulation functionalities.These additional functionalities,combined with the increased electron throughput of these devices,permit all-optical on-chip manipulation of electron beams in a fully integrated architecture compatible with current fabrication technologies,which opens the way to unconventional electron beam shaping,imaging,and radiationg encration.

Angle-selective perfect absorption with two-dimensional materials

Two-dimensional(2D)materials have great potential in photonic and optoelectronic devices.However,the relatively weak light absorption in 2D materials hinders their application in practical devices.Here,we propose a general approach to achieve angleselective perfect light absorption in 2D materials.As a demonstration of the concept,we experimentally show giant light absorption by placing large-area single-layer graphene on a structure consisting of a chalcogenide layer atop a mirror and achieving a total absorption of 77.6%in the mid-infrared wavelength range(~13μm),where the graphene contributes a record-high 47.2%absorptivity of mid-infrared light.Construction of such an angle-selective thin optical element is important for solar and thermal energy harvesting,photo-detection and sensing applications.Our study points to a new opportunity to combine 2D materials with photonic structures to enable novel device applications.

Structured 3D linear space–time light bullets by nonlocal nanophotonics

We propose the generation of 3D linear light bullets propagating in free space using a single passive nonlocal optical surface.The nonlocal nanophotonics can generate space–time coupling without any need for bulky pulse-shaping and spatial modulation techniques.Our approach provides simultaneous control of various properties of the light bullets,including the external properties such as the group velocity and the propagation distance,and internal degrees of freedom such as the spin angular momentum and the orbital angular momentum.

Light control with Weyl semimetals

Weyl semimetals are topological materials whose electron quasiparticles obey the Weyl equation.They possess many unusual properties that may lead to new applications.This is a tutorial review of the optical properties and applications of Weyl semimetals.We review the basic concepts and optical responses of Weyl semimetals,and survey their applications in optics and thermal photonics.We hope this pedagogical text will motivate further research on this emerging topic.