Quantum light–matter interfaces are at the heart of photonic quantum technologies. Quantum memories for photons, where non-classical states of photons are mapped onto stationary matter states and preserved for subsequent retrieval, are technical realizations enabled by exquisite control over interactions between light and matter. The ability of quantum memories to synchronize probabilistic events makes them a key component in quantum repeaters and quantum computation based on linear optics. This critical feature has motivated many groups to dedicate theoretical and experimental research to develop quantum memory devices. In recent years, exciting new applications, and more advanced developments of quantum memories, have proliferated. In this review, we outline some of the emerging applications of quantum memories in optical signal processing, quantum computation and non-linear optics. We review recent experimental and theoretical developments, and their impacts on more advanced photonic quantum technologies based on quantum memories.
: Conventional human-driven methods face limitations in designing complex functional metasurfaces. Inverse design is poised to empower metasurface research by embracing fast-growing arti fi cial intelligence. In recent years, many research e ff orts have been devoted to enriching inverse design principles and applications. In this perspective, we review most commonly used metasurface inverse design strategies including topology optimization, evolutionary optimization, and machine learning techniques. We elaborate on their concepts and working principles, as well as examples of their implementations. We also discuss two emerging research trends: scaling up inverse design for large-area aperiodic metasurfaces and end-to-end inverse design that co-optimizes photonic hardware and post-image processing. Furthermore, recent demonstrations of inverse-designed metasurfaces showing great potential in real-world applications are highlighted. Finally, we discuss challenges in future inverse design advancement, suggest potential research directions, and outlook opportunities for implementing inverse design in nonlocal metasurfaces, recon fi gurable metasurfaces, quantum optics, and nonlinear metasurfaces.
The on-chip implementation of optical nonlinear activation functions is crucial for realizing large-scale photonic neural chips. The use of nonlinear effects from two-photon absorption (TPA) allows for the realization of broadband, high-speed all-optical nonlinear activation functions. Here, we exploit the strong TPA coefficients and CMOS-process maturity of Group IV photonics to experimentally demonstrate low-loss silicon-on-insulator (SOI) and germanium-on-silicon (Ge-on-Si) waveguides as all-optical nonlinear activation units. The devices exhibit fast response frequency up to 100 and 300 MHz, respectively. Using the implemented nonlinear activation function, we investigated the performance of convolutional neural networks in classifying the MNIST handwritten digit image dataset, achieving accuracies of 97.88% (SOI) and 97.74% (Ge-on-Si). This verifies the effectiveness of our approach in handwritten digit classification tasks.
The study of optical vortex beams has garnered significant attention due to their wide-ranging applications. These beams exhibit a phase singularity and accurately identifying the location of the singular point is crucial for various vortex-based applications. This study introduces a novel method for localizing the phase singularity of optical vortex beams using a hybrid optical correlator. In contrast to machine learning-based techniques, the proposed approach eliminates the need for complex architectures, reducing computational demands and facilitating real-time implementation. The method demonstrates robust performance under varying conditions, including different contrast levels and aberrations such as astigmatism.
Accurate mapping of subterranean structures, particularly tunnels, is vital for infrastructure maintenance, safety inspections, and urban planning. Traditional methods such as total stations, LiDAR (Light Detection and Ranging), and Ground-Penetrating Radar (GPR) offer high precision but come with significant financial, logistical, and technical constraints. This paper presents a novel, cost-effective approach to underground structure mapping using the Emlid RX RTK (Real-Time Kinematic) GNSS (Global Navigation Satellite System) rover and the PIX4Dcatch mobile application, leveraging the capabilities of modern smartphones. By integrating GNSS RTK signals, photogrammetry algorithms, and the PIX4D AutoTag technology, the proposed method offers an accessible solution for accurate mapping in areas with limited GNSS signal availability. We demonstrate the feasibility of this method in real-world scenarios, highlighting its potential for enhancing productivity, scalability, and accuracy. This study also addresses the challenges of underground environments, such as poor lighting and sensor navigation, and suggests best practices for mobile phone-based mapping. Our results aim to provide a practical, affordable alternative to traditional tunnel mapping techniques, making them more accessible to users with limited photogrammetric knowledge.
This paper presents a combined theoretical and experimental method for noise suppression in the repetition frequency (<i>f<sub>r</sub></i>) locking of erbium-doped fiber optical frequency combs (OFCs). This study proposed a novel mathematical model to bridge the noise relationship of <i>f<sub>r</sub></i> between the free-running and locked modes, and analyzed this relationship from two perspectives: the additional phase noise and the frequency stability. In addition, to integrate theoretical modeling with experimental validation, this study designed <i>f<sub>r</sub></i> locking strategy that uses a phase-locked loop (PLL) with PFD + PIID (a phase frequency detector and a proportional, first-order integer, second-order integer, first-order differential controller). Under synchronization of the <i>f<sub>r</sub></i> with a microwave reference (REF), this study achieved OFC additional frequency stabilities of 2.81 × 10<sup>−15</sup>@1 s and 8.08 × 10<sup>−19</sup>@10,000 s at 200 MHz fundamental frequency locking and 4.25 × 10<sup>−16</sup>@1 s and 1.91 × 10<sup>−19</sup>@10,000 s at 1200 MHz harmonic locking. The simulated and experimental results are in good agreement, confirming the consistency of the theoretical model and experiment. This work provides a reliable theoretical model that can be used to predict stability for OFC locking and significantly improves the additional frequency stability of OFCs.
Davi F. Rêgo, Fabrício G. S. Silva, Rodrigo C. Gusmão
et al.
Artificial intelligence paradigms hold significant potential to advance nanophotonics. This study presents a novel approach to designing a plasmonic absorber using an artificial neural network as a surrogate model in conjunction with a genetic algorithm. The methodology involved numerical simulations of multilayered metal–dielectric plasmonic structures to establish a dataset for training an artificial neural network (ANN). The results demonstrate the proficiency of the trained ANN in predicting reflectance spectra and its ability to generalize intricate relationships between desired performance and geometric configurations, with values of correlation higher than 98% in comparison with ground-truth electromagnetic simulations. Furthermore, the ANN was employed as a surrogate model in a genetic algorithm (GA) loop to achieve target optical behaviors. The proposed methodology provides a powerful means of inverse designing multilayered metal–dielectric devices tailored for visible band wavelength filtering. This research demonstrates that the integration of AI-driven approaches in nanophotonics leads to efficient and effective design strategies.
Integrated photonic neural networks (PNNs) usually adopt traditional convolutional neural network (CNN) or multilayer perceptron (MLP) network models. These models consist of horizontally cascaded deep layer architectures interleaved by nonlinear activation functions. However, there are practical challenges for on-chip realizing such architectures, including the optical loss and the lack of efficient on-chip optical activation nonlinearity. Here, we propose a vertically hierarchical photonic neural network leveraging electro-optical element-wise multiplication to extract an element-wise feature in a polynomial projection space, which enables high-accuracy classification. For this network architecture, the light propagates through only two fully connected linear layers; thus, vertical extension to the deep layer is not limited by optical loss. This electro-photonic network can perform equivalently to or outperform optical CNN and MLP models even without interleaving deep layers by activation functions, benchmarking ∼97.9%, ∼87.7%, and ∼90.3% average blind-testing accuracies, for the whole test sets of MNIST handwritten digits, Fashion-MNIST images, and KMNIST Japanese cursive characters, respectively. It also demonstrates a >99% accuracy for boundary prediction of 12-labeled clusters. This work presents a different PNN architecture, which offers both high performance and better amenability to an integrated photonics platform.
We investigate photon transport in magnetically tunable fluids, specifically magnetic nanofluids and magnetorheological fluids (MRFs). Our study focuses on the statistical analysis of light transport in these fluids, with a particular focus on earlier theoretical proposals related to the possibility of Anderson localization in these systems. We employ a well-known mesoscopic quantifier, the generalized conductance, to assess the domain of light transport in these systems. Magnetic nanofluids, which contain nanometer-sized magnetite particles, exhibit weak scattering with no substantial consequence on conductance, regardless of the applied magnetic field. In contrast, magnetorheological fluids, a bidispersion of micrometer-sized magnetizable spheres in a magnetic nanofluid, show a decrease in conductance to values below unity as the magnetic field strength increases. This decrease occurs at the magnetic-field-induced photonic bandgap in MRFs, which plays a crucial role in the localization process and is characterized by reduced transmitted intensity, altered speckle patterns, and significant changes in intensity statistics. Our findings also highlight the temporal evolution of field-induced speckles, where the initial high correlation decreases over time, and the correlation width widens indicating that the duration of sustained correlation enhances as the system reaches equilibrium. Consequently, the evolution of field-induced scatterers in MRFs significantly emulates light localization effects as the system attains equilibrium. This study concludes that our system is a prime candidate to observe possible strong localization in a magnetically tunable, dissipative complex system. Such systems hold potential applications in optical switching, adaptive optics, and smart materials design through controlled light manipulation using external magnetic fields.
The article describes results of using a medical intraoral scanner Medit i500 to obtain odontological information in a course of the survey of the modern population in the western regions of the Republic of Tuva within the framework of the complex ethnographic and anthropological expedition of TuvSU-CPI under the leadership of E.V. Aiyzhi. The experience of using this scanner occurred to be very successful. From a technical point of view, the scanner demonstrated high efficiency and productivity due to the high scanning speed. The use of an intraoral scanner opens up wide methodological possibilities in conducting dental anthropology studies: first, the use of digital images for further analysis instead of wax prints, makes it possible to expand the research program by including a number of features of both the lingual and vestibular surfaces of the crowns, and the occlusive one. Secondly, the researcher has the opportunity to accurately fix the sequence and degree of teething of the permanent change, which is very important for determining the correspondence of the "dental" and passport age in children, which ultimately makes it possible to assess the processes of growth and development in the population. Thirdly, it allows us to study in more detail the morphology of the teeth, more accurately assess the severity score of the dental anthropology feature. In addition, thanks to the use of the scanner, we were able to carry out an important methodological study on the analysis of interobserver agreement in the assessment of some dental traits.
Alessandra Impellizzeri, Martina Horodynski, Gaspare Palaia
et al.
Background: The aim of this RCT is to show the effectiveness of laser technology for the exposure of palatally impacted canines, using a CO<sub>2</sub> or diode laser, and to evaluate the possible bio-stimulation effect of the laser on the spontaneous eruption of the canine. Methods: This study was carried out on a sample of 27 patients, divided randomly into three groups: treated with a CO<sub>2</sub> laser (Group A), treated with a diode laser (Group B), and treated with a cold blade (Group C). Monitoring was performed at 1, 8, and 16 weeks after surgery, through photo and digital scans performed with a CS3500 intraoral scanner. Results: It was found that the average total eruptions are 4.55 mm for Group A, 5.36 mm for Group B, and 3.01 mm for Group C. The difference in eruption between groups A and B is not significant. Comparing the laser groups with the control group, it has emerged that the difference in eruption is statistically significant. Conclusion: A significant tooth movement was observed in both Groups A and B. The response of the canine to the bio-stimulation of the laser can be considered effective, resulting in a statistically significant difference between the study groups and the control group. Both lasers have the same bio-stimulatory action on the eruption of canines.
Pulsed ytterbium-doped fiber amplifiers (YDFA) with ns-level signal width are important devices for obtaining high-power pulsed lasers. When some components in the amplifier are ineffective, e.g., the isolator or fiber is damaged, extra feedback light is generated and coupled into the gain fiber. The dynamic thermal distribution and waveform evolution of amplifiers with extra continuous-wave (CW) or pulse-wave (PW) feedback are theoretically analyzed in this work. The CW feedback can not only reduce the gain of the amplifier but can also change the thermal distribution of the gain fiber, while the PW feedback can reduce the leading or trailing edge of the output pulse by 3–4 ns, depending on the direction of the feedback light transmission. The theoretical analysis provides a reference for optimizing the thermal management and the fault diagnosis of a typical fiber amplifier with an output of several tens of watts.
Engineered domain structures play an essential role in nonlinear optics for quasi-phase-matched parametric processes. Pyroelectric field-assisted domain inversion with focused femtosecond laser pulses is a promising approach to create arbitrary two-dimensional nonlinear photonic structures in a large volume without externally applied electrical fields. We fabricate lattices of ferroelectric domains by patterning lithium niobate crystals with femtosecond laser pulses and then heating them to elevated temperatures. After cooling to room temperature, domains form below and above the laser-induced seeds. We investigate the effect of temperature and seed spacing on the number and size of inverted domains. In a temperature range of 220 °C-300 °C all domains are inverted in a two-dimensional lattice with periods of 15 µm × 6.3 µm. Smaller lattice periods result in a smaller fraction of inverted domains. Measurements with conducting, nonconducting, and short-circuited crystal surfaces reveal the influence of surface charges during the domain formation process. From the obtained domain widths and spacings, we calculate the effective nonlinear coefficient of quasi-phase-matched second-harmonic generation in two-dimensional nonlinear photonic structures.
We report on simulations carried out for an integrated phase corrector that can efficiently couple the light distorted by atmospheric turbulence into a single-mode fiber (SMF). The photonic integrated circuit (PIC) consists of a square array of surface grating couplers used to deflect the off-plane wave vector of the free-space beamlets into the plane of a single-mode waveguide in the chip. Resistive elements acting as heaters are subsequently used to stretch a coiled section of the individual waveguides and, in doing so, shift the phase of the propagating modes. With the correct phase shifts applied to the channels — each corresponding to a subaperture on a telescope pupil — the channels can be coherently combined, and the collected light can be delivered to one output SMF. In an adaptive optics (AO) system, the phase corrector would act as a deformable mirror (DM) commanded by a controller that takes phase measurements from a wavefront sensor (WFS).
Random phase screen method was used to simulate the light intensity and phase distribution of the synthesized double vortex beams transmitted in atmospheric turbulence given the light intensity characteristics and phase characteristics of double Laguerre–Gaussian beams (DLGB) generated by coaxial superposition. Results show that the scintillation coefficient decreases initially, and then increases with the topological charge difference of the double vortex beam, and the topological charge difference is related to the number of split spots. When the number of split spots is small, the intensity distribution is concentrated, exhibiting a good penetrating effect on atmospheric turbulence.
Yurii V. Filatov, Daniil G. Gilev, Polina S. Goncharova
et al.
Today, the task of developing microoptical gyroscopes is topical. Usually, tunable lasers with a built-in frequency stabilization system are used in such gyroscopes. They are comparatively bulky, which hinders the real miniaturization of optical gyroscopes. We propose a new approach implemented by using a Mach–Zehnder modulator with a passive ring resonator connected to one of its arms. This makes it possible to obtain a mutual configuration and makes the use of a tunable laser optional. Two ring resonators made of the polarization-maintaining fiber, suitable for use as sensitive elements of a gyroscope, were realized and investigated. Their Q-factor is equal to 14.5 × 10<sup>6</sup> and 28.9 × 10<sup>6</sup>. The maximum sensitivity of the proposed method when using the described resonators is 3.2 and 1.8 °/h, respectively. The first experimental setup of a resonator gyroscope implementing this approach has been manufactured and analyzed. When measuring the rotation speed by the quasi-harmonic signal span and its phase, the measurement accuracy was approximately 11 and 0.4 °/s, respectively.
High-quality, ultra-precise processing of surfaces is of high importance for high-tech industry and requires a good depth control of processing, a low roughness of the machined surface and as little as possible surface and subsurface damage but cannot be realized by laser ablation processes. Contrary, electron/ion beam, plasma processes and dry etching are utilized in microelectronics, optics and photonics. Here, we have demonstrated a laser-induced plasma (LIP) etching of single crystalline germanium by an optically pumped reactive plasma, resulting in high quality etching. A Ti:Sapphire laser (λ = 775 nm, EPulse/max. = 1 mJ, t = 150 fs, frep. = 1 kHz) has been used, after focusing with a 60 mm lens, for igniting a temporary plasma in a CF4/O2 gas at near atmospheric pressure. Typical etching rate of approximately ~ 100 nm / min and a surface roughness of less than 11 nm rms were found. The etching results were studied in dependence on laser pulse energy, etching time, and plasma – surface distance. The mechanism of the etching process is expected to be of chemical nature by the formation of volatile products from the chemical reaction of laser plasma activated species with the germanium surface. This proposed laser etching process can provide new processing capabilities of materials for ultra—high precision laser machining of semiconducting materials as can applied for infrared optics machining.