Deep-learning-empowered synthetic dimension dynamics:morphing of light into topological modes

Synthetic dimensions(SDs)opened the door for exploring previously inaccessible phenomena in high-dimensional space.However,construction of synthetic lattices with desired coupling properties is a challenging and unintuitive task.Here,we use deep learning artificial neural networks(ANNs)to construct lattices in real space with a predesigned spectrum of mode eigenvalues,and thus to validly design the dynamics in synthetic mode dimensions.By employing judiciously chosen perturbations(wiggling of waveguides at desired frequencies),we show resonant mode coupling and tailored dynamics in SDs.Two distinct examples are illustrated:one features uniform synthetic mode coupling,and the other showcases the edge defects that allow for tailored light transport and confinement.Furthermore,we demonstrate morphing of light into a topologically protected edge mode with modified Su-Schrieffer-Heeger photonic lattices.Such an ANN-assisted construction of SDs may advance toward“utopian networks,”opening new avenues for fundamental research beyond geometric limitations as well as for applications in mode lasing,optical switching,and communication technologies.

Terahertz surface plasmonic waves: a review

Terahertz science and technology promise many cutting-edge applications.Terahertz surface plasmonic waves that propagate at metal–dielectric interfaces deliver a potentially effective way to realize integrated terahertz devices and systems.Previous concerns regarding terahertz surface plasmonic waves have been based on their highly delocalized feature.However,recent advances in plasmonics indicate that the confinement of terahertz surface plasmonic waves,as well as their propagating behaviors,can be engineered by designing the surface environments,shapes,structures,materials,etc.,enabling a unique and fascinating regime of plasmonic waves.Together with the essential spectral property of terahertz radiation,as well as the increasingly developed materials,microfabrication,and time-domain spectroscopy technologies,devices and systems based on terahertz surface plasmonic waves may pave the way toward highly integrated platforms for multifunctional operation,implementation,and processing of terahertz waves in both fundamental science and practical applications.We present a review on terahertz surface plasmonic waves on various types of supports in a sequence of properties,excitation and detection,and applications.The current research trend and outlook of possible research directions for terahertz surface plasmonic waves are also outlined.

White-light emission from organic aggregates:a review

White light,which contains polychromic visible components,affects the rhythm of organisms and has the potential for advanced applications of lighting,display,and communication.Compared with traditional incandescent bulbs and inorganic diodes,pure organic materials are superior in terms of better compatibility,flexibility,structural diversity,and environmental friendliness.In the past few years,polychromic emission has been obtained based on organic aggregates,which provides a platform to achieve white-light emission.Several white-light emitters are sporadically reported,but the underlying mechanistic picture is still not fully established.Based on these considerations,we will focus on the single-component and multicomponent strategies to achieve efficient white-light emission from pure organic aggregates.Thereinto,single-component strategy is introduced from four parts:dual fluorescence,fluorescence and phosphorescence,dual phosphorescence with anti-Kasha’s behavior,and clusteroluminescence.Meanwhile,doping,supramolecular assembly,and cocrystallization are summarized as strategies for multicomponent systems.Beyond the construction strategies of white-light emitters,their advanced representative applications,such as organic light-emitting diodes,white luminescent dyes,circularly polarized luminescence,and encryption,are also prospected.It is expected that this review will draw a comprehensive picture of white-light emission from organic aggregates as well as their emerging applications.

Infrared upconversion imaging in nonlinear metasurfaces

Infrared imaging is a crucial technique in a multitude of applications,including night vision,autonomous vehicle navigation,optical tomography,and food quality control.Conventional infrared imaging technologies,however,require the use of materials such as narrow bandgap semiconductors,which are sensitive to thermal noise and often require cryogenic cooling.We demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas,using a nonlinear wave-mixing process.We experimentally show the upconversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation.In this process,an infrared image of a target is mixed inside the metasurface with a strong pump beam,translating the image from the infrared to the visible in a nanoscale ultrathin imaging device.Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.

Neuromorphic silicon photonics with 50 GHz tiled matrix multiplication for deep-learning applications

The explosive volume growth of deep-learning(DL)applications has triggered an era in computing,with neuromorphic photonic platforms promising to merge ultra-high speed and energy efficiency credentials with the brain-inspired computing primitives.The transfer of deep neural networks(DNNs)onto silicon photonic(SiPho)architectures requires,however,an analog computing engine that can perform tiled matrix multiplication(TMM)at line rate to support DL applications with a large number of trainable parameters,similar to the approach followed by state-of-the-art electronic graphics processing units.Herein,we demonstrate an analog SiPho computing engine that relies on a coherent architecture and can perform optical TMM at the record-high speed of 50 GHz.Its potential to support DL applications,where the number of trainable parameters exceeds the available hardware dimensions,is highlighted through a photonic DNN that can reliably detect distributed denial-of-service attacks within a data center with a Cohen’s kappa score-based accuracy of 0.636.

Optical waveguiding along nanometer slits

Optical field confinement is a topic of immense interest in optical sci-ence and technology.Shrinking and confining an optical wave in spatial dimensions not only reduces the size of its footprint,but greatly enhan-ces its field strength in the confined region,leading to stronger light–matter interaction.

Deterministic all-optical quantum state sharing

Quantum state sharing,an important protocol in quantum information,can enable secure state distribution and reconstruction when part of the information is lost.In(k,n)threshold quantum state sharing,the secret state is encoded into n shares and then distributed to n players.The secret state can be reconstructed by any k players(k>n∕2),while the rest of the players get nothing.In the continuous variable regime,the implementation of quantum state sharing needs the feedforward technique,which involves opticelectro and electro-optic conversions.These conversions limit the bandwidth of the quantum state sharing.Here,to avoid the optic-electro and electro-optic conversions,we experimentally demonstrate(2,3)threshold deterministic all-optical quantum state sharing.A low-noise phase-insensitive amplifier based on the four-wave mixing process is utilized to replace the feedforward technique.We experimentally demonstrate that any two of three players can cooperate to implement the reconstruction of the secret state,while the rest of the players cannot get any information.Our results provide an all-optical platform to implement arbitrary(k,n)threshold deterministic all-optical quantum state sharing and pave the way to construct the all-optical broadband quantum network.

About the cover: Advanced Photonics Volume 2, Issue 1

The image on the cover for Advanced Photonics Volume 2,Issue 1,demonstrates the principle of compressed ultrafast photography via image encoding and decoding.The dynamic scene(shock wave)is spatially encoded by DMD and temporally sheared by streak camera,which is recovered through a compressed sensing algorithm with a high imaging speed of a trillion frames per second.Provided by S.Zhang et al.,a team of researchers from East China Normal University,the image is based on the research presented in their article,“Single-shot compressed ultrafast photography:a review,”Adv.Phot.2(1)014003。

Two-channel, dual-beam-mode, wavelength-tunable femtosecond optical parametric oscillator

Optical vortices,which carry orbital angular momentum,offer special capabilities in a host of applications.A single-laser source with dual-beam-mode output may open up new research fields of nonlinear optics and quantum optics.We demonstrate a dual-channel scheme to generate femtosecond,dualwavelength,and dual-beam-mode tunable signals in the near infrared wavelength range.Dual-wavelength operation is derived by stimulating two adjacent periods of a periodically poled lithium niobate crystal.Pumped by an Yb-doped fiber laser with a Gaussian(lp?0)beam,two tunable signal emissions with different beam modes are observed simultaneously.Although one of the emissions can be tuned from1520 to 1613 nm with the Gaussian(ls?0)beam,the other is capable of producing a vortex spatial profile with different vortex orders(ls?0 to 2)tunable from 1490 to 1549 nm.The proposed system provides unprecedented freedom and will be an exciting platform for super-resolution imaging,nonlinear optics,multidimensional quantum entanglement,etc.

Ultrafast and real-time physical random bit extraction with all-optical quantization

Optical chaos generated by perturbing semiconductor lasers has been viewed,over recent decades,as an excellent entropy source for fast physical random bit generation(RBG)owing to its high bandwidth and large random fluctuations.However,most optical-chaos-based random bit generators perform their quantization process in the electrical domain using electrical analog-to-digital converters,so their real-time rates in a single channel are severely limited at the level of Gb/s due to the electronic bottleneck.Here,we propose and experimentally demonstrate an all-optical method for RBG where chaotic pulses are quantized into a physical random bit stream in the all-optical domain by means of a length of highly nonlinear fiber.In our proof-of-concept experiment,a 10-Gb/s random bit stream is successfully generated on-line using our method.Note that the single-channel real-time rate is limited only by the chaos bandwidth.Considering that the Kerr nonlinearity of silica fiber with an ultrafast response of few femtoseconds is exploited for composing the key part of quantizing laser chaos,this scheme thus may operate potentially at much higher real-time rates than 100 Gb/s provided that a chaotic entropy source of sufficient bandwidth is available.

Resolving and weighing the quantum orbits in strong-field tunneling ionization

Tunneling ionization of atoms and molecules induced by intense laser pulses contains the contributions of numerous quantum orbits.Identifying the contributions of these orbits is crucial for exploring the application of tunneling and for understanding various tunneling-triggered strong-field phenomena.We perform a combined experimental and theoretical study to identify the relative contributions of the quantum orbits corresponding to the electrons tunneling ionized during the adjacent rising and falling quarter cycles of the electric field of the laser pulse.In our scheme,a perturbative second-harmonic field is added to the fundamental driving field.By analyzing the relative phase dependence of the signal in the photoelectron momentum distribution,the relative contributions of these two orbits are unambiguously determined.Our results show that their relative contributions sensitively depend on the longitudinal momentum and modulate with the transverse momentum of the photoelectron,which is attributed to the interference of the electron wave packets of the long orbit.The relative contributions of these orbits resolved here are important for the application of strong-field tunneling ionization as a photoelectron spectroscopy for attosecond time-resolved measurements.

Air-core fiber distribution of hybrid vector vortex-polarization entangled states

Entanglement distribution between distant parties is one of the most important and challenging tasks in quantum communication.Distribution of photonic entangled states using optical fiber links is a fundamental building block toward quantum networks.Among the different degrees of freedom,orbital angular momentum(OAM)is one of the most promising due to its natural capability to encode high dimensional quantum states.We experimentally demonstrate fiber distribution of hybrid polarization-vector vortex entangled photon pairs.To this end,we exploit a recently developed air-core fiber that supports OAM modes.High fidelity distribution of the entangled states is demonstrated by performing quantum state tomography in the polarization-OAM Hilbert space after fiber propagation and by violations of Bell inequalities and multipartite entanglement tests.The results open new scenarios for quantum applications where correlated complex states can be transmitted by exploiting the vectorial nature of light.

High-capacity free-space optical link in the midinfrared thermal atmospheric windows using unipolar quantum devices

Free-space optical communication is a very promising alternative to fiber communication systems,in terms of ease of deployment and costs.Midinfrared light has several features of utter relevance for free-space applications:low absorption when propagating in the atmosphere even under adverse conditions,robustness of the wavefront during long-distance propagation,and absence of regulations and restrictions for this range of wavelengths.A proof-of-concept of high-speed transmission taking advantage of intersubband devices has recently been demonstrated,but this effort was limited by the short-distance optical path(up to 1 m).In this work,we study the possibility of building a long-range link using unipolar quantum optoelectronics.Two different detectors are used:an uncooled quantum cascade detector and a nitrogen-cooled quantum well-infrared photodetector.We evaluate the maximum data rate of our link in a back-to-back configuration before adding a Herriott cell to increase the length of the light path up to 31 m.By using pulse shaping,pre-and post-processing,we reach a record bitrate of 30 Gbit s−1 for both two-level(OOK)and four-level(PAM-4)modulation schemes for a 31-m propagation link and a bit error rate compatible with error-correction codes.

Nonlinear thermal emission and visible thermometry

The control of thermal emission is of great importance for emerging applications in energy conversion and thermometric sensing.Usually,thermal emission at ambient temperature is limited to the midto far-infrared,according to the linear theory of Planck’s law.We experimentally demonstrate a broadband nonlinear thermal emission in the visible-NIR spectrum within a quadradic nonlinear medium,which emits visible thermal radiation through a pump-driven nonlinear upconversion from its mid-IR components even at room temperature,unlike its linear counterpart which requires ultrahigh temperature.The broadband emission is enabled by the crucial random quasi-phase-matching condition in our nonlinear nanocrystal powders.Moreover,nonlinear thermal emission also permits visible thermometry using traditional optical cameras instead of thermal ones.This scheme paves the way to understand thermal radiation dynamics with nonlinearity in many fields,such as nonlinear heat transfer and nonlinear thermodynamics.

About the cover: Advanced Photonics Volume 2, Issue 3

The image on the cover for Advanced Photonics Volume 2,Issue 3,illustrates precise THz spectroscopy using a lowcomplexity dual-comb fiber laser,in which the blurry vibrational absorption spectrum of gas molecules is clearly resolved by the adaptive sampling dual-comb method.The image is based on the original research presented in the article by Jie Chen,Kazuki Nitta,Xin Zhao,Takahiko Mizuno,Takeo Minamikawa,Francis Hindle,Zheng Zheng,and Takeshi Yasui:“Adaptive-sampling near-Doppler-limited terahertz dualcomb spectroscopy with a free-running single-cavity fiber laser,”Adv.Photon.2(3),036004.

Perturbation-driven echo-like superfluorescence in perovskite superlattices

The collective response of macroscopic quantum states under perturbation is widely used to study quantum correlations and cooperative properties,such as defect-induced quantum vortices in Bose–Einstein condensates and the non-destructive scattering of impurities in superfluids.Superfluorescence(SF),as a collective effect rooted in dipole–dipole cooperation through virtual photon exchange,leads to the macroscopic dipole moment(MDM)in high-density dipole ensembles.However,the perturbation response of the MDM in SF systems remains unknown.Echo-like behavior is observed in a cooperative exciton ensemble under a controllable perturbation,corresponding to an initial collapse followed by a revival of the MDM.Such a dynamic response could refer to a phase transition between the macroscopic coherence regime and the incoherent classical state on a time scale of 10 ps.The echo-like behavior is absent above 100 K due to the instability of MDM in a strongly dephased exciton ensemble.Experimentally,the MDM response to perturbations is shown to be controlled by the amplitude and injection time of the perturbations.

Submilliwatt, widely tunable coherent microcomb generation with feedback-free operation

Microcombs are revolutionizing optoelectronics by providing parallel, mutually coherent wavelengthchannels for time-frequency metrology and information processing. To implement this essential function inintegrated photonic systems, it is desirable to drive microcombs directly with an on-chip laser in a simpleand flexible way. However, two major difficulties have prevented this goal: (1) generating mode-lockedcomb states usually requires a significant amount of pump power and (2) the requirement to align laser andresonator frequency significantly complicates operation and limits the tunability of the comb lines. Here, weaddress these problems by using microresonators on an AlGaAs on-insulator platform to generate dark-pulsemicrocombs. This highly nonlinear platform dramatically relaxes fabrication requirements and leads to arecord-low pump power of <1 mW for coherent comb generation. Dark-pulse microcombs facilitated bythermally controlled avoided mode crossings are accessed by direct distributed feedback laser pumping.Without any feedback or control circuitries, the comb shows good coherence and stability. With around150 mW on-chip power, this approach also leads to an unprecedentedly wide tuning range of over one freespectral range (97.5 GHz). Our work provides a route to realize power-efficient, simple, and reconfigurablemicrocombs that can be seamlessly integrated with a wide range of photonic systems.

Photonic implementation of boson sampling:a review

Boson sampling is a computational problem that has recently been proposed as a candidate to obtain an unequivocal quantum computational advantage.The problem consists in sampling from the output distribution of indistinguishable bosons in a linear interferometer.There is strong evidence that such an experiment is hard to classically simulate,but it is naturally solved by dedicated photonic quantum hardware,comprising single photons,linear evolution,and photodetection.This prospect has stimulated much effort resulting in the experimental implementation of progressively larger devices.We review recent advances in photonic boson sampling,describing both the technological improvements achieved and the future challenges.We also discuss recent proposals and implementations of variants of the original problem,theoretical issues occurring when imperfections are considered,and advances in the development of suitable techniques for validation of boson sampling experiments.We conclude by discussing the future application of photonic boson sampling devices beyond the original theoretical scope.

Quantum interference with independent single-photon sources over 300 km fiber

In the quest to realize a scalable quantum network,semiconductor quantum dots(QDs)offer distinct advantages,including high single-photon efficiency and indistinguishability,high repetition rate(tens of gigahertz with Purcell enhancement),interconnectivity with spin qubits,and a scalable on-chip platform.However,in the past two decades,the visibility of quantum interference between independent QDs rarely went beyond the classical limit of 50%,and the distances were limited from a few meters to kilometers.Here,we report quantum interference between two single photons from independent QDs separated by a 302 km optical fiber.The single photons are generated from resonantly driven single QDs deterministically coupled to microcavities.Quantum frequency conversions are used to eliminate the QD inhomogeneity and shift the emission wavelength to the telecommunication band.The observed interference visibility is 0.670.02(0.930.04)without(with)temporal filtering.Feasible improvements can further extend the distance to∼600 km.Our work represents a key step to long-distance solid-state quantum networks.

Applications of thin-film lithium niobate in nonlinear integrated photonics

Photonics on thin-film lithium niobate(TFLN)has emerged as one of the most pursued disciplines within integrated optics.Ultracompact and low-loss optical waveguides and related devices on this modern material platform have rejuvenated the traditional and commercial applications of lithium niobate for optical modulators based on the electro-optic effect,as well as optical wavelength converters based on secondorder nonlinear effects,e.g.,second-harmonic,sum-,and difference-frequency generations.TFLN has also created vast opportunities for applications and integrated solutions for optical parametric amplification and oscillation,cascaded nonlinear effects,such as low-harmonic generation;third-order nonlinear effects,such as supercontinuum generation;optical frequency comb generation and stabilization;and nonclassical nonlinear effects,such as spontaneous parametric downconversion for quantum optics.Recent progress in nonlinear integrated photonics on TFLN for all these applications,their current trends,and future opportunities and challenges are reviewed.