Topological characteristics, including invariant topological orders, band inversion, and the topological edge mode (TEM) in photonic insulators, have been widely studied. Whether intriguing topological modes can be taken advantage of in simple one-dimensional systems to implement some practical applications is an issue, which is of increasing concern. In this work, based on a photonic dimer chain composed of ultrasubwavelength resonators, we verify experimentally that the TEM in the effective second-order parity-time (PT) system is immune to the inner disorder perturbation, and can be used to realize the long-range wireless power transfer (WPT) with high transmission efficiency. To intuitively show the TEM can be used for WPT, a power signal source is used to excite the TEM. It can be clearly seen that two light-emitting diode (LED) lamps with 0.5 W at both ends of the structure are lit up with the aid of TEMs. In addition, in order to solve the special technical problems of standby power loss and frequency tracking, we further propose that a WPT system with effective third-order PT symmetry can be constructed by using one topological interface mode and two TEMs. Inspired by the long-range WPT with TEMs in this work, the use of more complex topological structures is expected to achieve energy transmission with more functions, such as the WPT devices whose direction can be selected flexibly in the quasiperiodic or trimer topological chains.

Harnessing the spontaneous emission of incoherent quantum emitters is one of the hallmarks of nano-optics. Yet, an enduring challenge remains—making them emit vector beams, which are complex forms of light associated with fruitful developments in fluorescence imaging, optical trapping, and high-speed telecommunications. Vector beams are characterized by spatially varying polarization states whose construction requires coherence properties that are typically possessed by lasers—but not by photons produced by spontaneous emission. Here, we show a route to weave the spontaneous emission of an ensemble of colloidal quantum dots into vector beams. To this end, we use holographic nanostructures that impart the necessary spatial coherence, polarization, and topological properties to the light originating from the emitters. We focus our demonstration on vector vortex beams, which are chiral vector beams carrying nonzero orbital angular momentum, and argue that our approach can be extended to other forms of vectorial light.

Non-Hermitian skin effect (NHSE) has led to interesting physics and sophisticated applications beyond the conventional framework. However, NHSE studies have been limited to an individual dimension due to the difficulty of constructing nonreciprocal coupling in higher-dimensional systems. With the concept of synthetic dimension, we realize two-dimensional (2D) NHSE in a synthetic photonic lattice. The synthetic photonic lattice is composed of a spatial dimension and a synthetic frequency dimension, which is constructed by introducing gain and loss and dynamically modulating the complex refractive index in a one-dimensional ring-resonator array. In the synthetic 2D NHSE system, we can manipulate the spatial position and frequency mode of the light in real time, thus enabling programmable light propagation and frequency conversion. Specifically, the incident light can be localized in the spatial dimension and the frequency dimension simultaneously, leading to second-order corner modes in the synthetic 2D NHSE lattice. Besides, the 2D NHSE system exhibits an excellent robustness for the disorder and point defect in the lattice. This work generalizes the non-Hermitian skin effect in synthetic dimension to control the light in different dimensions, which shows great promise for potential applications in on-chip light manipulation, frequency synthesis, and information processing.

We demonstrate highly sensitive photon counting in the infrared region based on two-photon absorption (2PA) in a silicon avalanche photodiode, where the required photon energy for inducing effective conductivity is provided by an intense midinfrared (MIR) field at 3 $\mu \mathrm{m}$. The used MIR pumping scheme can not only benefit from the enhanced 2PA coefficient in the nondegenerate regime, but also eliminate the detrimental background noises due to the pump harmonic excitation of the pump. Consequently, the enhancement factor for the signal counting rate unprecedentedly reached about ${10}^5$ with input infrared pulses at the femtojoule level. Additionally, the noise equivalent power is substantially improved by 2 orders of magnitude in comparison to conventional schemes with near-infrared pumping. Therefore, the presented configuration might provide an alternative to realize sensitive infrared detection and imaging with desirable features of room-temperature operation, no phase-matching requirement, and broadband responding window, which can find a variety of applications, including remote ranging, sensitive sensing, biochemical imaging, and trace spectroscopy.

Enhancing the measurement signal from solid-state quantum sensors such as the nitrogen-vacancy (N-$V$) center in diamond is a challenge for sensing and imaging of condensed-matter systems. Here we design and fabricate diamond scanning probes with a truncated parabolic profile that optimizes the photonic signal from single, near-surface, embedded N-$V$ centers, forming a high-sensitivity probe for nanoscale magnetic field imaging. These structures operate over the full N-$V$ photoluminescence spectrum with the emission being directed into a measured numerical aperture of 0.44. Furthermore, they yield a median saturation count rate of 2.1 MHz, a fivefold improvement in measurement signal over the state of the art in scanning-probe-based N-$V$ sensors. We additionally introduce a charge-state-registered pulsed-excitation method for measuring the detection efficiency of photons from the N-$V$’s metrologically relevant negative charge state, finding an overall detection efficiency of $12\mathrm{\%}$. We demonstrate the excellent properties of these diamond scanning probes by imaging thin-film ferromagnetic stripes with a spatial resolution better than 50 nm.

Quantum memory is the core device for the construction of large-scale quantum networks. For scalable and convenient practical applications, integrated optical memories, especially on-chip optical memories, are crucial requirements because they can be easily integrated with other on-chip devices. Here, we report the coherent optical memory based on a type-IV waveguide fabricated on the surface of a rare-earth ion-doped crystal (i.e., $\mathrm{E}{\mathrm{u}}^{3+}$:${\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$). The properties of the optical transition (${}^7{\mathrm{F}}_0\to {}^5{\mathrm{D}}_0$) of the ${\mathrm{Eu}}^{3+}$ ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of $97\pm 1\mathrm{\%}$ between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.

Plasmonic nanopores are the subject of extensive investigations as a potential platform to enable efficient optical readout in translocation experiments with biomolecules such as DNA and proteins. They allow for the engineering of electromagnetic fields at the nanoscale, which are typically used to enhance the emission efficiency of fluorescent molecules. Their features make them suitable for detection strategies based on the energy transfer between translocating molecules and the nanopore itself. Here, we carry out an optical experiment to show that a handful of diffusing dyes acting as donors can exchange energy via Förster-resonance energy transfer (FRET) with a gold nanopore functionalized with dyes behaving as acceptors. The FRET pair is composed of ATTORho6G (donor) and Alexa610 (acceptor). To perform this proof-of-concept experiment, we use a gold nanopore with a diameter of 80 nm, prepared on a ${\text{Si}}_3{\text{N}}_4$ membrane. We observe that the presence of the acceptors on the walls of the nanopore reduces the lifetime of the diffusing donors. In addition, we observe that the presence of the acceptors reduces the fluorescence signal on the donor detection channel and increases the fluorescence signal on the acceptor detection channel. The combination of these three effects gives us enough evidence to claim that the diffusing donors exchange energy with the functionalized nanopore via FRET, despite the relatively large size of the nanopore. The FRET efficiency of the process is found to be of the order of $30\mathrm{\%}$, which is in fairly good agreement with a theoretical value obtained using a simplified model.

Unidirectional wave propagation in nonreciprocal structures enables exciting opportunities to control and enhance wave-matter interactions in extreme ways. Within this context, here we investigate the possibility of using terminated unidirectional plasmonic waveguides to enhance typically weak nonlinear effects by orders of magnitude. We theoretically demonstrate remarkable levels of electric field enhancement and confinement (field hot spots) when the unidirectional waveguiding structure is terminated with a suitable boundary that fully stops the one-way mode. Such a large field enhancement, originating from a nonresonant effect, is fundamentally different from the narrow-band field concentration effects in resonant plasmonic structures. Instead, it is analogous to the broadband response of plasmonic tapers, but without the need for any adiabatic impedance matching. We show that this effect can indeed lead to a substantial boosting of nonlinear light-matter interactions, exemplified by an improvement of several orders of magnitude in the third-harmonic-generation efficiency, which is of large significance for several applications. More broadly, our findings show the potential of extreme nonreciprocal configurations for enhanced wave-matter interactions.

We investigate the demonstration and quantification of the strong coupling between excitons and guided photons in a $\mathrm{Ga}\mathrm{N}$ slab waveguide. The dispersions of waveguide polaritons are measured from $T=6$ to 300 K through gratings. They are carefully analyzed within four models based on different assumptions, in order to assess the strong-coupling regime. We prove that the guided photons and excitons are strongly coupled at all investigated temperatures, with a small $(11\mathrm{\%})$ dependence on the temperature. However, the values of the Rabi splitting strongly vary among the four models: the “coupled oscillator” model overestimates the coupling; the analytical “Elliott-Tanguy” model precisely describes the dielectric susceptibility of $\mathrm{Ga}\mathrm{N}$ near the excitonic transition, leading to a Rabi splitting equal to $82\pm 10$ meV for fundamental transverse-electric mode; the experimental ellipsometry-based model leads to smaller values of $55\pm 6$ meV. We evidence that, for waveguides including active layers with large oscillator strengths, as required for room-temperature polaritonic devices, a strong bending of the modes’ dispersion is not necessarily the signature of the strong coupling, which requires for its reliable assessment a precise analysis of the material dielectric susceptibility.

Compact chip-scale comb sources are of significant interest for many practical applications. Here, we experimentally study the generation of supercontinuum (SC) in an axially varying integrated waveguide. We show that the local tuning of the dispersion enables the continuous blue shift of dispersive waves by more than 200 nm due to their trapping by the strongly compressed pump pulse. This mechanism provides an insight into supercontinuum generation in varying-dispersion integrated waveguides. Pumped close to 2.2 $\mu \mathrm{m}$ in the femtosecond regime and at a pulse energy of approximately 4 pJ, the output spectrum extends from 1.1 $\mu \mathrm{m}$ up to 2.76 $\mu \mathrm{m}$ and shows good coherence properties. Octave-spanning SC is also observed at an input energy as low as approximately 0.9 pJ. We show that the supercontinuum is more robust against variations of the input-pulse parameters and is also spectrally flatter in waveguides with an optimized dispersion profile than in dispersion-engineered ones. This research demonstrates the potential of varying-dispersion waveguides for coherent SC generation and paves the way for integrated low-power applications, such as chip-scale frequency-comb generation, precision spectroscopy, optical-frequency metrology, and wide-band wavelength division multiplexing in the near infrared.

Exceptional points (EPs) in photonics are associated with non-Hermitian Hamiltonians with energy gain or loss, a notable example is EPs in parity-time symmetric Hamiltonians. We show that, counterintuitively, actual energy gain or loss is not required to generate this type of non-Hermitian degeneracy, since the eigenvalue of the optical Hamiltonian is the mode's propagation constant and not the energy. This is demonstrated by a simple three-layer insulator-metal-insulator (I-M-I) plasmonic waveguide, the eigenmodes of which are known to experience degeneracy at a certain point in the parametric space suggested to be used for rainbow trapping. We identify this point to be, in fact, an EP with the coalescence of the eigenmodes, despite the system having neither parity nor time symmetry. Furthermore, we demonstrate the manifestation of a third-order EP, which is generated by merging two separate EPs in the parametric space of the I-M-I waveguide. The presented results reveal unconventional properties of the Hamiltonian of a simple plasmonic waveguide and provide an insight into the nature of EPs in non-Hermitian plasmonic systems in general, suggesting the possibility of accessing even higher-order EP regimes in simple photonic structures without the need for optical gain or loss.

Quantum optics and nanophotonics are the basis of future communications and computation technologies. Thus, there is an ever-increasing need for analysis and design tools that are suitable for large, complex, and multielement systems. However, full quantum analysis of systems requires writing the full quantum Hamiltonian, which is usually possible only in simple cases that are easy to analyze analytically, and especially difficult when the system contains dispersive and dissipative elements. Here we use circuit theory to modularize the modeling of the quantum Hamiltonian, and therefore the entire quantum system. We use the notion of optical metatronics—circuit analog for nanophotonic structures—to model our photonic system as an electronic circuit, and show how each coupling term in the Hamiltonian can be written using classical equivalent circuits. Thus, the quantum-interaction term between any two elements can be analyzed, designed, and optimized using the vast library of circuit engineering tools, which by their very nature enable the design of complex, multielement realistic systems. Our work generalizes the current theoretical treatment of quantized nanophotonic systems, paving the way for a systemic, modularized modeling of large-scale systems.

Plasmonic lattices consisting of nanoparticles in a homogeneous environment are well known for their support of so-called surface lattice resonances. They are associated with localized surface plasmons coupled to each other via photons propagating freely along the structure. Interestingly, such structures provide narrow resonances in plasmonic structures without their coupling to any external high-$Q$ resonators. In this paper, we explore modes in a stack of two identical plasmonic lattices. We demonstrate that such a structure is able to support a mode that is positioned strictly on a Rayleigh anomaly and does not shift with the variation of distance between two lattices over wide limits. Given the fact that the period is the most stably reproduced quantity in an experiment, such behavior can be used to simplify the fabrication of structures with resonances at desired energies. The application of this effect can be very useful in lasing, light emission from metasurfaces, optical filters, and many other optical devices.

The interplay of high operating temperatures and good heat dissipation is crucial for high-performance terahertz quantum cascade lasers. We therefore study the influence on the cross-plane thermal conductivity of different aluminum concentrations in the barrier of ${\mathrm{Ga}\mathrm{As}/\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ active regions. The thermal conductivity is decreasing from $30\mathrm{W}{\mathrm{K}}^{-1}{\mathrm{m}}^{-1}$ to $12\mathrm{W}{\mathrm{K}}^{-1}{\mathrm{m}}^{-1}$ if the aluminum concentration is increased from 15% to 24%. The temperature during pulsed-laser operation is obtained by measuring the variation of the emission frequency for different laser pulse lengths. This shows, that besides the thermal conductivity, the amount of electric input power has a strong influence on the temperature reached internally during laser operation and is critical for creating high-power devices operating at high temperatures. We show that active regions with thin but high ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ barriers fulfill this need and are well suited for high-temperature operation. A thermal model of the devices allows prediction of the active-region temperature increase for very short pulse durations. For the structure with 24% Al barriers and a starting temperature of 10 K, the model shows an increase by 24 K for a pulse length of only 300 ns.

Large-scale spiking neural networks have been designed based on superconducting-nanowire single-photon detectors (SNSPDs) as receiver elements for photonic communication between artificial neurons and synapses. Such large-scale artificial neural networks will require thousands of waveguide-integrated SNSPD devices on a single chip. Efficient waveguide-coupled SNSPDs and high-throughput methods for their characterization at this scale are very challenging. Here, we design, fabricate, and measure SNSPDs that are compatible with these large-scale networks. We demonstrate integrated-photonic circuits to simultaneously characterize many waveguide-coupled SNSPDs with a single-fiber input. We achieve up to 15 waveguide-coupled SNSPDs in a single integrated-photonic circuit and a total of 49 waveguide SNSPDs with a detection plateau out of 49 tested. This is perhaps the largest number of SNSPDs integrated in a photonic circuit to date. We employ several types of photonic circuits to enable rapid and reliable characterization of detector performance. We further demonstrate several important synaptic functions of these detectors. These include a binary response in the detectors with average incident photon numbers ranging from less than ${10}^{-3}$ to greater than 10, indicating that synaptic responses based on these detectors are independent of the number of incident photons in a communication pulse. Such a binary response is ideal for communication in neural systems. We further demonstrate that the response has a linear dependence of the output-current pulse height on the bias current with up to a factor of 1.7 tunability in pulse height, a function that cannot be obtained without a detection plateau.

The realization of robust strong coupling and entanglement between distant quantum emitters (QEs) is necessary for scalable quantum-information processes. However, it is hard to achieve it based on conventional systems. Here, we propose theoretically and demonstrate numerically a scheme to realize such strong coupling and entanglement. Our scheme is based on the photonic crystal platform with topologically protected edge state and zero-dimensional topological corner cavities. When the QEs are put into topological cavities, the strong coupling between them can be fulfilled with the assistance of the topologically protected interface state. Such a strong coupling can maintain a very long distance and be robust against various defects. In particular, we numerically prove that the topologically protected entanglement between two QEs can also be realized. Moreover, the duration of quantum beats for such entanglement can reach several orders longer than that for the entanglement in a conventional photonic cavity, making it beneficial for a scalable quantum-information process.

On-chip integration fundamentally changes the way in which information is processed. The exploding communication capacity requires a high degree of integration of optical devices in a limited footprint. These requirements have pushed the minimization of optical chips almost to their physical limits. One potential way to break this limitation is to increase the number of functionalities in a module, for which the most critical issue is to expand the degree of freedom of information processing. Here, we propose a degree of freedom of information processing based on the basic mode vectors in the anti-parity-time-symmetry system. Based on our principle, adjacent whispering-gallery modes in a ring cavity are remarkably distinguished in their sensitivity to the signal intensity. What is more, the desired modes are labeled by individual resonance frequencies. This principle is demonstrated experimentally based on the wavelength-selective nonlinear excitation in microring resonators with the nonlinear material ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. In addition, the combination of this proposed degree of freedom and the signal-direction-dependent function is experimentally demonstrated. This research provides a degree of freedom for designing multifunction devices, which will fundamentally expand the capacity of on-chip information processing.

Neural networks based on machine learning can interpolate well within the training dataset, but their ability to extrapolate is severely limited by fundamental issues such as the bias-variance trade-off. Here we introduce the concept of an operator parameter space consisting of physical entities encoded with Maxwell’s equations to improve the networks’ capability to generalize beyond their training set. We illustrate the idea with photonic crystals, and show that the network trained with operator parameters yields remarkably accurate predictions of the topological transitions both within and beyond the training physical space. Such concepts can be generalized to higher-dimensional wave structures by choosing the appropriate operator parameters.

Personal radiative thermal management using photonic smart textiles has become a center of attention due to its potential to facilitate thermal comfort, and to decrease the energy cost for heating and cooling. Here, we provide an approach for a dynamic transmittance switch textile (DTST): a dynamic, passive, radiative thermal regulating fabric that controls the infrared (IR) transmission by adapting to the ambient temperature and humidity. The DTST is constituted from metal-coated monofilaments and stimuli-responsive polymer actuator beads, in this way benefiting from multiple IR photonic effects to strongly control the wide-band transmission of thermal radiation and to provide for a sharp, dynamic response. This design shows a wide dynamic ambient setpoint temperature window of approximately $16{}^{\circ }\mathrm{C}$, meaning that the wearer is comfortable between 9.5 and $25.7{}^{\circ }\mathrm{C}$, wider than any theoretically reported or fabricated switchable fabric. This performance indicates a polyvalent user comfort and an important energy saving potential for residential and office buildings.