Volume 14, Issue 15

Nonlinear integrated photonics, which takes advantage of the strong field enhancement in integrated waveguides to boost the efficiency of nonlinear effects, has paved the way for the demonstration of cutting-edge applications. These achievements have also been made possible by the impressive progress in material engineering and fabrication processes, which have enabled a remarkable control of the nonlinear dynamics in the waveguides. While researchers initially focused their attention on single-mode devices, in recent years, the exploitation of nonlinear effects in integrated multimode waveguides has attracted significant interest. Indeed, the simultaneous use of different spatial modes of the same multimode waveguide has opened new avenues in the realization of integrated nonlinear processors, thanks to the ability to tune the dispersion profiles of the different modes. In this review, we discuss the most recent advances in nonlinear multimode photonics on-chip. In the first part, we review the use of intermodal nonlinear effects for frequency generation. The use of intermodal nonlinear effects has been extensively reported, for example, for wavelength conversion for telecom applications, generation of photon pair sources for quantum optics and mid-infrared frequency generation. Then, we discuss several demonstrations of nonlinear multimode waveguides used to perform simultaneous multi-channel and multi-functional optical signal processing, such as nonlinear switching and logic operations. Next, supercontinuum generation in nonlinear multimode waveguides will be discussed. Finally, we report the use of high-quality-factor micro-resonators based on multimode waveguides for the realization of compact and widely-tunable integrated Raman lasers and optical frequency comb sources with record-low threshold power.

Optical imaging and single-molecule imaging, in particular, utilize fluorescent tags in order to differentiate observed species by color. The degree of color multiplexing is dependent on the available spectral detection window and the ability to distinguish between fluorophores of different colors within this window. Consequently, most single-molecule imaging techniques rely on two to four colors for multiplexing. DeepQR combines compact spectral imaging with deep learning to enable 4 color acquisition with only 3 spectral detection windows. It allows rapid high-throughput acquisition and decoding of hundreds of unique single-molecule color combinations applied here to tag native RNA targets. We validate our method with clinical samples analyzed with the NanoString gene-expression inflammation panel side by side with the commercially available NanoString nCounter system. We demonstrate high concordance with “gold-standard” filter-based imaging and over a four-fold decrease in acquisition time by applying a single snapshot to record four-color barcodes. The new approach paves the path for extreme single-molecule multiplexing.

Semiconductor nanowires can enhance the signal of fluorescent molecules, thus significantly improving the limits of fluorescence detection in optical biosensing. In this work, we explore how the sensitivity can further be enhanced through “digital” detection of adequately spaced vertically aligned nanowires, employing single-emitter localization methods, and bright-field microscopy. Additionally, we introduce a systematic analysis pipeline aimed at harnessing this digital detection capability and evaluate its impact on detection sensitivity. Using a streptavidin-biotin assay, we demonstrate that single-emitter localization expands the dynamic range to encompass five orders of magnitude, enabling detections of concentrations ranging from 10 fM to 10 nM. This represents two to three orders of magnitude improvement in detection compared to methods that do not utilize single-emitter localization. We validate our analysis framework by simulating an artificial dataset based on numerical solutions of Maxwell’s equations. Furthermore, we benchmark our results against total internal reflection fluorescence microscopy and find, in time-resolved titration experiments, that nanowires offer higher sensitivity at the lowest concentrations, attributed to a combination of higher protein capture rate and higher intensity per single protein binding event. These findings suggest promising applications of nanowires in both endpoint and time-resolved biosensing.

Biological neural network functionality depends on the vast number of connections between nodes, which can be challenging to implement artificially. One radical solution is to replace physical wiring with broadcasting of signals between the artificial neurons. We explore an implementation of this concept by light emitting/receiving III-V semiconductor nanowire neurons in a quasi-2D waveguide. They broadcast light in anisotropic patterns and specific regions in the nanowires are sensitised to exciting and inhibiting light signals. Weights of connections between nodes can then be tailored using the geometric light absorption/emission patterns. Through detailed simulations, we determine the connection strength based on rotation and separation between the nanowires. Our findings reveal that complex weight distributions are possible, indicating that specific neuron geometric patterns can achieve highly variable connectivity as needed for neural networks. An important design parameter is matching the wavelength to the specific physical dimensions of the network. To demonstrate applicability, we simulate a reservoir neural network using a hexagonal pattern of nanowires with random angular orientations, displaying its ability to perform chaotic time series prediction. The design is compatible with integration on Si substrates and can be extended to other nanophotonic components.

Recent advances in perovskite crystals have highlighted their exceptional optical properties, making them promising candidates for a wide range of photonic applications. However, the exploration of high-repetition-rate laser systems based on these materials remains underdeveloped, hindering their potential in ultrafast laser technologies and related fields such as optical communications and precision metrology. In this study, we present, for the first time, the saturable absorption characteristics of a novel organic–inorganic hybrid perovskite incorporating the heavy metal bismuth (Bi), specifically N-methylbenzothiazoleBiI 4 (BtzBiI 4 ). The material was integrated as a saturable absorber (SA) into a passively mode-locking erbium-doped fiber laser. By harnessing the exceptional optical nonlinearity of BtzBiI 4 -SA, we successfully achieved stable fundamental mode-locking, harmonic mode-locking, and bound-state soliton mode-locking within a single cavity. The fundamental mode-locking yielded pulses with a duration of 844 fs and a signal-to-noise ratio of 66.15 dB. Additionally, the 142nd-order harmonic solitons attained an impressive repetition rate of 1.3202 GHz. These results represent a significant step forward in the realization of high-repetition-rate fiber lasers utilizing perovskite materials. Our findings highlight the remarkable potential of BtzBiI 4 as a high-performance nonlinear optical material, paving the way for next-generation ultrafast photonic devices.

Antibiotic detection at trace levels in different matrices is an important tool for environmental monitoring, clinical diagnostics, and pharmaceutical quality control. Using aluminum concavities covered with silver nanoparticles (AgNPs), this study introduces another approach for the surface-enhanced Raman spectroscopy (SERS) detection of antibiotics. The optimal substrate provided by the aluminum concavities and the outstanding plasmonic enhancement of the AgNPs greatly enhances the adsorbed Raman signals of the antibiotic molecules. First, we used a controlled magnetron sputtering technique to deposit AgNPs onto the SERS substrates, synthesized by anodizing aluminum into highly organized concave dimensions. Detection limits approaching the 10 −10  M concentration level, owing to an EF of 10 8 , proved that these substrates successfully detected various antibiotics, including amoxicillin and tetracycline. An in-depth examination of the SERS spectra revealed distinctive peaks that correspond to functional groups, allowing for the exact identification and quantification of the antibiotic compounds. The synergistic impact of the aluminum concavities and silver nanofractals results in extremely homogenous substrates that are reproducible and sensitive.

Recent advancements have broadened the application of photon filters based on Bragg gratings within optical communication networks and optical input/output interfaces. Traditional gratings, however, suffer from a fixed refractive index modulation distribution once manufactured, constraining their adaptability and flexibility. This study introduces a reconfigurable multi-channel photon filter on a silicon nitride on insulator platform. The filter incorporates an equivalent linearly chirped four-phase-shifted sampled Bragg grating with micro-heaters to enable thermo-optic tuning, facilitating programmable control over transmission spectral features. Experimental outcomes indicate the filter’s capability to seamlessly transition among single, dual, and quad-band configurations, as well as a band-stop mode, with independent tuning of each band. Moreover, optical frequency division multiplexing experiments using a 50 GHz semiconductor mode-locked laser have affirmed the filter’s tunability. In quad-band mode, band separations of 50, 100, and 150 GHz are achievable; in dual and single-band modes, band intervals extend from 150 to 250 GHz, allowing for precise single-wavelength selection. Featuring high tunability, minimal insertion losses, and superior signal side-mode suppression ratio, this filter structure supports the integration of programmable photonic devices into space optical communications, photonic integrated networks, and elastic optical networks.

The stable on-chip deterministic arbitrary-phase-controlling of signal light in micro/nanometer spatial scale is an extremely important basis for large-scale and high-density integrated photonic information processing chips. Conventional phase-controlling methods face with serious limitation of unavoidable crosstalk, length distortion, and fabrication error. To date, it is still a great challenge to achieve deterministic and wide-range on-chip arbitrary-phase-controlling. Here, we report an effective strategy of three-waveguide coupled configuration to realize on-chip deterministic arbitrary-phase-controlling (ranging from 0 to 2 π ) by combing the dynamic phase and the geometric phase. Based on this strategy, quantum gate operations in an optical permutation-group circuit are successfully realized in femtosecond-laser direct writing sample. To extend the feasibility of this method, on-chip silicon-based deterministic arbitrary-phase-controlling in the optical communication range is also experimentally verified. Our work not only paves the way for fundamental research in chip-scale novel optical devices but also promotes the study of topological quantum computing.

Cathodoluminescence (CL) microscopy has emerged as a powerful tool for investigating the optical properties of materials at the nanoscale, offering unique insights into the behavior of photonic and plasmonic materials under electron excitation. We introduce an atlas of bulk CL spectra and intensity for a broad range of materials used in photonics and plasmonics. Through a combination of experimental CL microscopy and Monte Carlo simulations, we characterize spectra and intensity of coherent and incoherent CL, electron penetration depth and energy deposition, offering a foundational reference for interpreting CL signals and understanding material behavior under electron excitation. Our atlas captures CL signals across a wide range of materials, offering valuable insight into intrinsic emission properties for informed material selection and device design in photonics and plasmonics.

This paper presents a metasurface-based light receiver tailored for compact off-axis light detection and ranging (LiDAR) systems, addressing the critical challenge of simultaneously enhancing the field of view (FOV) and effective signal reception while adhering to strict size and weight limitations. A general design principle for the metasurface-based light receiver with large FOV capability is proposed, leveraging mapping relations to achieve optimal performance. As a proof of concept, a 20-mm-diameter 4-region metasurface device was designed and fabricated by deep ultraviolet (DUV) projection stepper lithography on an 8-inch fused silica wafer. The metasurface-based light receiver achieves a large FOV of ±30° and demonstrates a significant power enhancement ranging from 1.5 to 3 times at 940 nm when coupled with a 3-mm-diameter avalanche photodiode (APD). The innovation not only establishes a new paradigm for compact, high-performance LiDAR systems but also enables deployment in advanced fields such as unmanned aerial vehicles (UAVs) and miniaturized robots.

We directly characterize nanoscale spatiotemporal inhomogeneities of multi-layered molybdenum diselenide (MoSe 2 ) in real space and time – the nanometre–femtosecond scale, attributing to local mechanical structures such as strain and surface/subsurface defects, which are critical in semiconductor and optoelectronic applications. This remarkable precision is achieved through the development of a hyper-temporal transient nanoscopy incorporating a sideband-coupled generalized lock-in amplification technique, allowing for characterization of local spatiotemporal defects at each pixel within a subwavelength mapping region. By utilizing this technique, we characterize the nanoscale strain-induced spatiotemporal defects of multi-layered MoSe 2 , including nano-bubbles that exhibit a noticeable reduction in exciton-exciton annihilation rates, which may attribute to the suppressed probability of bimolecular interaction of excitons due to the strain-induced band distortion. Moreover, we visualize topographically hidden spatiotemporal defects such as lattice mismatches, which induce mid-gap states that traps charge carriers and thereby slow down recombination process. We propose that this hyper-temporal approach to resolving intricate spatiotemporal inhomogeneities in van der Waals materials provides significant insights into their optoelectronic properties and opens new avenues for innovative material design and characterization.

Bessel beams hold significant potential in optical communications, particle manipulation, and medicine due to their self-healing and nondiffracting properties. However, most existing Bessel beam generation devices are either static or capable of dynamically adjusting only a single characteristic. In this paper, we propose a tunable Bessel beam generation scheme based on a moiré meta-device. The device consists of two cascaded layers of all-dielectric metasurfaces. By adjusting the relative rotation between two layers, Bessel beams with varying topological charges can be generated. Moreover, the overall rotation of the cascaded metasurfaces modulates the polarization state of the Bessel beam by leveraging both the propagation phase and geometric phase. Experimental results confirmed the generation of Bessel beams with tunable uniform linear polarization and topological charge, as well as Bessel beams with tunable topological charge and controllable polarization variations along the propagation direction. This method offers a flexible design strategy for the continuous dynamic manipulation of both the transverse and longitudinal optical field properties of Bessel beams. In addition, it may also advance the development of related fields, including optical communications, particle manipulation, and super-resolution imaging.