Photonic Technologies Research Articles

Polaritonic states trapped by topological defects

The miniaturization of photonic technologies calls for a deliberate integration of diverse materials to enable novel functionalities in chip-scale devices. Topological photonic systems are a promising platform to couple structured light with solid-state matter excitations and establish robust forms of 1D polaritonic transport. Here, we demonstrate a mechanism to efficiently trap mid-IR structured phonon-polaritons in topological defects of a metasurface integrated with hexagonal boron nitride (hBN). These defects, created by stitching displaced domains of a Kekulé-patterned metasurface, sustain localized polaritonic modes that originate from coupling of electromagnetic fields with hBN lattice vibrations. These 0D higher-order topological modes, comprising phononic and photonic components with chiral polarization, are imaged in real- and Fourier-space. The results reveal a singular radiation leakage profile and selective excitation through spin-polarized edge waves at heterogeneous topological interfaces. This offers impactful opportunities to control light-matter waves in their dimensional hierarchy, paving the way for topological polariton shaping, ultrathin structured light sources, and thermal management at the nanoscale.

Multimodal deep learning using on-chip diffractive optics with in situ training capability

Multimodal deep learning plays a pivotal role in supporting the processing and learning of diverse data types within the realm of artificial intelligence generated content (AIGC). However, most photonic neuromorphic processors for deep learning can only handle a single data modality (either vision or audio) due to the lack of abundant parameter training in optical domain. Here, we propose and demonstrate a trainable diffractive optical neural network (TDONN) chip based on on-chip diffractive optics with massive tunable elements to address these constraints. The TDONN chip includes one input layer, five hidden layers, and one output layer, and only one forward propagation is required to obtain the inference results without frequent optical-electrical conversion. The customized stochastic gradient descent algorithm and the drop-out mechanism are developed for photonic neurons to realize in situ training and fast convergence in the optical domain. The TDONN chip achieves a potential throughput of 217.6 tera-operations per second (TOPS) with high computing density (447.7 TOPS/mm2), high system-level energy efficiency (7.28 TOPS/W), and low optical latency (30.2 ps). The TDONN chip has successfully implemented four-class classification in different modalities (vision, audio, and touch) and achieve 85.7% accuracy on multimodal test sets. Our work opens up a new avenue for multimodal deep learning with integrated photonic processors, providing a potential solution for low-power AI large models using photonic technology.

Characterization of quantum dot-like emitters in programmable arrays of nanowrinkles of 1L-WSe2

When combined with nanostructured substrates, two-dimensional semiconductors can be engineered with strain to tailor light–matter interactions on the nanoscale. Recently, room-temperature nanoscale exciton localization with controllable wrinkling in 1L-WSe2 was achieved using arrays of gold nanocones. Here, the characterization of quantum dot-like states and single-photon emitters in the 1L-WSe2/nanocone system is reported. The nanocones induce a wide range of strains, and as a result, a diverse ensemble of narrowband, potential single-photon emitters is observed. The distribution of emitter energies reveals that most reside in two spectrally isolated bands, leaving a less populated intermediate band that is spectrally isolated from the ensembles. The spectral isolation is advantageous for high-purity quantum light emitters, and anti-bunched emission from one of these states is confirmed up to 25 K. Although the spatial distribution of strain is expected to influence the orientation of the transition dipoles of the emitters, multimodal emission polarization anisotropy and atomic force microscopy reveal that the macroscopic orientation of the wrinkles is not a good predictor of dipole orientation. Finally, the emission is found to change with thermal cycling from 4 to 290 K and back to 4 K, highlighting the need to control factors such as temperature-induced strain to enhance the robustness of this quantum emitter platform. The initial characterization here shows that controlled nanowrinkles of 1L-WSe2 generate quantum light in addition to uncovering potential challenges that need to be addressed for their adoption into quantum photonic technologies.

Purifying Photon Indistinguishability through Quantum Interference.

Indistinguishability between photons is a key requirement for scalable photonic quantum technologies. We experimentally demonstrate that partly distinguishable single photons can be purified to reach near-unity indistinguishability by the process of quantum interference with ancillary photons followed by heralded detection of a subset of them. We report on the indistinguishability of the purified photons by interfering two purified photons and show improvements in the photon indistinguishability of 2.774(3)% in the low-noise regime, and as high as 10.2(5)% in the high-noise regime.

Integrated Photonic Sensors for the Detection of Toxic Gasses—A Review

Gas sensing is crucial for detecting hazardous gasses in industrial environments, ensuring safety and preventing accidents. Additionally, it plays a vital role in environmental monitoring and control, helping to mitigate pollution and protect public health. Integrated photonic gas sensors are important due to their high sensitivity, rapid response time, and compact size, enabling precise recognition of gas concentrations in real-time. These sensors leverage photonic technologies, such as waveguides and resonators, to enhance performance over traditional gas sensors. Advancements in materials and fabrication techniques could further improve their efficiency, making them invaluable for environmental monitoring, industrial safety, and healthcare diagnostics. In this review, we delved into photonic gas sensors that operate based on the principles of evanescent field absorption (EFA) and wavelength interrogation methods. These advanced sensing mechanisms allow for highly sensitive and selective gas detection, leveraging the interplay of light with gas molecules to produce precise measurements.

Artificial intelligence and machine learning in optics: tutorial

Across the spectrum of scientific inquiry and practical applications, the emergence of artificial intelligence (AI) and machine learning (ML) has comprehensively revolutionized problem-solving methodologies. This tutorial explores key aspects of AI/ML and their remarkable role in augmenting the capabilities of optics and photonics technologies. Beginning with fundamental definitions and paradigms, the tutorial progresses to classical machine learning algorithms, with examples employing support vector machines and random forests. Extensive discussion of deep learning encompasses the backpropagation algorithm and artificial neural networks, with examples demonstrating the applications of dense and convolutional neural networks. Data augmentation and transfer learning are examined next as effective strategies for handling scenarios with limited datasets. Finally, the necessity of alleviating the burden of data collection and labeling is discussed, motivating the investigation of unsupervised and semi-supervised learning strategies as well as the utilization of reinforcement learning. By providing a structured exploration of AI/ML techniques, this tutorial equips researchers with the essential tools to begin leveraging AI’s transformative potential within the expansive realm of optics and photonics.

Triple Plexcitonic Nonreciprocity of Magnetochiral Plexcitons.

Nonreciprocal quantum devices, allowing different transmission efficiencies of light-matter polaritons along opposite directions, are key technologies for modern photonics, yet their miniaturization and fine manipulation remain an open challenge. Here, we report on magnetochiral plexcitons dressed with geometric-time double asymmetry in compact nonreciprocal hybrid metamaterials, leading to triple plexcitonic nonreciprocity with flexible controllability. A general magnetically dressed plexcitonic Born-Kuhn model is developed to reveal the hybrid optical nature and dynamic energy evolution of magnetochiral plexcitons, demonstrating a plexcitonic nonreciprocal mechanism originating from the strong coupling among photon, electron, and spin degrees of freedom. Moreover, we introduce the temperature-controlled knob/switch for magnetochiral plexcitons, achieving precise magnetochiral control and nonreciprocal transmission in a given system. We expect this mechanism and approach to open up a new route for the integration and fine control of on-chip nonreciprocal quantum devices.

Distributed Bragg reflector based ASE noise removal pump wavelength filters for futuristic chip-scale quantum photonic circuits.

This article reports a novel design of a compact tunable resonance filter with a highly extinguished and ultra-broad out-of-band rejection for on-chip amplified spontaneous noise suppression from pump lasers highly demanding for generating pure/entangled photon pairs via χ(3) process in a CMOS compatible silicon photonics technology platform. The proposed device is designed with two identically apodized distributed grating structures for guided Fabry-Perot resonant transmissions in a silicon-on-insulator rib waveguide structure. The device design parameters are optimized by theoretical simulation for a low insertion loss singly-resonant transmission peak at a desired wavelength. We observed that a device length of as low as ∼ 35 µm exhibits a rejection band as large as ∼ 60 nm with an extinction of ∼ 40 dB with respect to the resonant wavelength peak at λr ∼ 1550 nm (FWHM ∼ 80 pm, IL ∼ 2 dB). The experimental results have been shown to be closely matching to our theoretical simulation and modeling results in terms of its stop bandwidth and resonance wavelength for noise suppressed pump laser wavelength filtering. As expected from the theoretical prediction, the trend pertaining to the trade-off between passive insertion loss and Q-value of the resonances has been observed depending on the device parameters. The thermo-optic tuning characteristics of resonant wavelengths have been obtained by integrating microheaters. The resonance peak could be tuned at a rate of 96 pm per mW of consumed thermal power. Noise associated with an amplified pump wavelength (λP ∼ 1550 nm) has been shown to be suppressed (∼ 40-dB), up to the detector noise floor.

Low‐Defect Quantum Dot Lasers Directly Grown on Silicon Exhibiting Low Threshold Current and High Output Power at Elevated Temperatures

The direct growth of III‐V materials on silicon is a key enabler for developing monolithically integrated lasers, offering substantial potential for ultradense photonic integration in vital communications and computing technologies. However, the III‐V/Si lattice and thermal expansion mismatch pose significant hurdles, leading to defects that degrade lasing performance. This study overcomes this challenge, demonstrating InAs/GaAs‐on‐Si lasers that perform on par with top‐tier lasers on native GaAs substrates. This is achieved through a newly developed epitaxial approach comprising a series of rigorously optimized growth strategies. Atomic‐resolution scanning tunneling microscopy and spectroscopy experiments reveal exceptional material quality in the active region and elucidate the impact of each growth strategy on defect dynamics. The optimized III‐V‐on‐silicon ridge‐waveguide lasers demonstrate a continuous‐wave threshold current as low as 6 mA and high‐temperature operation reaching 165 °C. At 80 °C, critical for data center applications, they maintain a 12 mA threshold and 35 mW output power. Furthermore, lasers fabricated on both Si and GaAs substrates using identical processes exhibit virtually identical average threshold current. By eliminating the performance limitations associated with the GaAs/Si mismatch, this study paves the way for robust and high‐density integration of a broad spectrum of critical III‐V photonic technologies into the silicon ecosystem.

Artificial Perovskite Multiple Quantum Well Optoelectronics

Metal halide perovskite-based photovoltaics and light-emitting diodes (LEDs) have exhibited a promising trajectory toward commercial viability, nearing the performance levels of them to the commercially established materials. A particularly encouraging avenue involves tailoring the various dimensions of perovskite materials, notably through the implementation of perovskite multiple quantum wells (MQWs), to amplify their potential in optoelectronic applications. This comprehensive review delves into recent breakthroughs in both self-assembled perovskite MQWs and artificially fabricated counterparts, elucidating their mechanisms and performance characteristics. By gathering and evaluating the very original and the latest research findings, this review aims to provide valuable insights into the underlying principles governing optical behaviors of perovskite MQWs as well as optoelectronic and photonic applications. Furthermore, it outlines prospective research pathways, delineating potential pathways for further exploration and optimization of perovskite MQW-based devices. Through this general evaluation on the recent advancements and prospects, this review contributes to advancing the understanding and application of perovskite materials in next-generation optoelectronic and photonic technologies.

Pencil lead etched by plasma: Novel photonic material that can control the reflection from the visible to the infrared region

The development of surface processing technology that modulate the intensity of light reflection over a wide wavelength range has important implications for the application of photonics technology. We previously reported that plasma irradiation to a pencil lead formed structural colors. This phenomenon occurs by the thin-layer interference between the clay in the pencil lead exposed by the plasma etching and the surface graphite of the sample. We now report that a pencil lead irradiated with plasma for a long time becomes a new photonic material that caused interference in the near-infrared or mid-infrared range. The thickness of the clay layer exposed by the plasma etching increased with the increment of the plasma irradiation time, and the reflection spectra in the near-infrared and mid-infrared ranges were changed by the light interferences. In addition, the reflection spectrum pattern of the plasma-treated sample well agreed with the simulated pattern based on a thin-layer interference model. According to this method, photonic materials with the desired reflectance over a wide wavelength range can be produced by varying the plasma irradiation time. Furthermore, the irradiation time required to produce the desired optical material can be estimated by the simulation. The infrared reflective area can be easily controlled by using a masking plastic plate. With this method, we succeeded in forming letters on the sample that could only be read by an infrared camera.

Investigating the influence of cerium doping on the structural, optical and electrical properties of ZnNiMgFe2-xCexO4 soft ferrites

The present work reports the optical, structural, and electrical properties of cerium-doped Zn0.6Ni0.2Mg0.2Fe2-xCexO4 soft ferrites by green synthesis method that unwrap transformative insights and find technological applications through X-ray diffraction (XRD), UV visible spectroscopy and IV-point probe techniques. Ferrites with different cerium concentrations (x = 0.0, 0.0250, 0.0375) show an enormous difference in the optical, structural, and electrical behavior of the ferrites. The crystallite size increases to 46.9 nm, with a concomitant increase in lattice constants up to 8.550 Å for x = 0.0375. A similar structural shift was noticed in X-ray and bulk densities from 5.031 to 4.982 g/cm³ and 3.83 to 3.97 g/cm³, respectively. The optical explorations revealed a remarkable bandgap reduction from 2.768 eV to 2.758 eV improving the utility of the material substantially in magneto-optic devices. Conversely, the refractive index increases from 2.420 to 2.423, and the imaginary dielectric constant goes up from 10.654 to 10.667, giving a herald of advancement in photonic technologies. Electrically, the study marks a drastic reduction in DC resistivity from 1.95 × 105 to 6.13 × 103 ohm-cm with the Ce doping, which indicates higher conductivity suitable for telecommunication. This extensive work on Ce-doped soft ferrites now opens up newer avenues of applications in electronics and magneto-optics, blending scientific inquiry with practical utility.

Progress and Outlooks in Designing Photonic Biosensor for Virus Detection

AbstractThe recent outbreak of coronavirus disease 2019 (COVID‐19) highlights the critical need for rapid, sensitive, and accurate virus detection methods to prevent and manage pandemics. Among the available sensing methods, photonic biosensors have emerged as a forefront technology, characterized by their high sensitivity, minimal analyte requirements, and suitability for miniaturization, making them ideal for point‐of‐care applications in virus detection. This review comprehensively summarizes the recent progress of photonic biosensor technologies, focusing on wavelength shift and luminescence‐based mechanisms. Their operational principles, general configurations, and the challenges associated with these technologies are looked into. An overview of the material developments used in photonic biosensors, encompassing organic, inorganic, and hybrid composite‐based materials is further presented. The discussion extends to surface functionalization using biorecognition elements, including DNA/RNA, aptamers, and antibodies, to craft the specificity of the photonic biosensors for viruses. Ultimately, the importance of a multidisciplinary approach is emphasized in developing new materials architecture, biological receptors, and modifications to photonic methods, aiming to realize better biosensors for virus detection with ultra‐high sensitivity, rapid response, and excellent selectivity.

Switchable and Tunable Radiative Cooling: Mechanisms, Applications, and Perspectives.

The cost of annual energy consumption in buildings in the United States exceeds 430 billion dollars ( Science 2019, 364 (6442), 760-763), of which about 48% is used for space thermal management (https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019), revealing the urgent need for efficient thermal management of buildings and dwellings. Radiative cooling technologies, combined with the booming photonic and microfabrication technologies ( Nature 2014, 515 (7528), 540-544), enable energy-free cooling by radiative heat transfer to outer space through the atmospheric transparent window ( Nat. Commun. 2024, 15 (1), 815). To pursue all-season energy savings in climates with large temperature variations, switchable and tunable radiative coolers (STRC) have emerged in recent years and quickly gained broad attention. This Perspective introduces the existing STRC technologies and analyzes their benefits and challenges in future large-scale applications, suggesting ways for the development of future STRCs.

Phase-resolved measurement and control of ultrafast dynamics in terahertz electronic oscillators

As a key component for next-generation wireless communications (6 G and beyond), terahertz (THz) electronic oscillators are being actively developed. Precise and dynamic phase control of ultrafast THz waveforms is essential for high-speed beam steering and high-capacity data transmission. However, measurement and control of such ultrafast dynamic process is beyond the scope of electronics due to the limited bandwidth of the electronic equipment. Here we surpass this limit by applying photonic technology. Using a femtosecond laser, we generate offset-free THz pulses to phase-lock the electronic oscillators based on resonant tunneling diode. This enables us to perform phase-resolved measurement of the emitted THz electric field waveform in time-domain with sub-cycle time resolution. Ultrafast dynamic response such as anti-phase locking behaviour is observed, which is distinct from in-phase stimulated emission observed in laser oscillators. We also show that the dynamics follows the universal synchronization theory for limit cycle oscillators. This provides a basic guideline for dynamic phase control of THz electronic oscillators, enabling many key performance indicators to be achieved in the new era of 6 G and beyond.

Enhancing optical modulator and link performance through modulation instability: design, simulation and implementation

In future optical communication applications, broadband tools and technologies are essential for increasing transfer and processing speeds. Conventional microwave tools are too slow and inflexible to meet these demands. Photonic microwave technology offers that most current solution to this issue, utilizing modulation tools to convert microwave signals to the optical domain. However, these modulation tools face significant challenges, including low bandwidth and high voltage requirements. Although various methods have been proposed in recent decades to address these issues, most increase structural complexity and cost without significantly improving modulator performance and bandwidth. In this article, by using a modulation instability in optical fibers, without manipulating and complicating the structure of the modulator and only by using common modulators, their bandwidth was multiplied and the required voltage was significantly reduced. Finally, a special fiber channel was designed, which showed a much better performance.

Design of a Photonic Crystal Exclusive-OR Gate Using Recurrent Neural Networks

In this paper, a novel approach to design a photonic crystal exclusive-OR (XOR) gate with high performance using recurrent neural network (RNN) is proposed, integrating the principles of symmetry and asymmetry inherent in photonic structures. The proposed model realizes the nonlinearities and dispersion properties in photonic systems, optimizing the waveguide paths and interference patterns to improve the performance of the logic gate. Simulation results demonstrate that the presented RNN design not only achieves high fidelity in the logical operation but also significantly enhances the functionality of the all-optical gate. This integration of machine learning with photonic crystal technology opens a new era for developing compact, energy-efficient photonic circuits for high-speed optical computing. Finally, the performance of the designed all-optical gate is compared with other related methods, which shows that the proposed gate outperforms other works. The results show that the obtained output power of the proposed all-optical XOR gate is 0, 0.813, 0.82, and 1 × 10−7 in the logical states.

Fiber Optic Devices for Diagnostics and Therapy in Photomedicine

AbstractPhotonic technologies have made enormous impacts on modern medicine, advancing disease diagnostics and treatments as well as health monitoring. A long‐standing challenge in the use of light and its widespread effects in photomedicine is the finite penetration of light in tissues. However, judiciously engineered optical fibers helped overcome this challenge and advance light delivery to deep tissues with spatial precision and desired accessibility. In recent years, the development of photonic technologies including optical biomaterials, fiber functionalization, and biomedical device innovations has greatly expanded the scope of light‐based healthcare. Here, the fundamentals and materials of fiber optics to endow themselves with biocompatibility, flexibility, and diverse functionalities required for long‐term implantation are overviewed. The design strategies of lab‐on‐fiber techniques, operation requirements to construct fiber optic sensors, and their health monitoring applications as wearable and implantable devices are presented. The use of fiber optics in major light‐based therapeutic modalities including optogenetics, photodynamic therapy, photobiomodulation, photochemical cross–linking, and photothermal therapy is illustrated to enhance their effectiveness, specificity, and feasibility. In short, a comprehensive review is provided on the fiber optic techniques and the latest photonic devices, which are envisioned to evolve photomedicine in clinical and point‐of‐care practices.

Observation of topologically enhanced third harmonic generation in doubly resonant nonlinear topolectrical circuits

The ability to confine and guide wave makes topological physics a promising platform for large local field enhancement and strong scattering immunity, which enables efficient nonlinear processes. In this research, we employ a mirror-stacking approach to achieve resonance through two distinct frequency localized states (LSs) in one-dimensional topological circuits, introducing a novel method for validating topological states to facilitate harmonic enhancement. Experimental results reveal that the harmonic wave power increases significantly, by two orders of magnitude, when both the fundamental and harmonic waves are in LSs, in contrast to cases where only one wave is localized. The conversion efficiency is 15.7 times that when the fundamental wave is in a localized state and the harmonic is in a transmission mode. This method, leveraging double-resonance in topological LSs, not only advances harmonic generation in topolectrical circuits but also opens up possibilities for innovative applications in the broader field of photonic technology.

Monolayer Semiconductor Superlattices with High Optical Absorption.

Optical absorption plays a central role in optoelectronic and photonic technologies. Strongly absorbing materials are thus needed for efficient and miniaturized devices. A uniform film much thinner than the wavelength can only absorb up to 50% of the incident light when embedded in a symmetric and homogeneous environment. Although deviating from these conditions allows higher absorption, finding the thinnest possible material with the highest intrinsic absorption is still desirable. Here, we demonstrate strong absorption by artificially stacking WS2 monolayers into superlattices. We compare three simple approaches based on different spacer materials to surpass the peak absorptance of a single WS2 monolayer, which stands at 16% on ideal substrates. Through direct monolayer stacking without an intentional spacer, we reach an absorptance of 27% for an artificial bilayer, although with limited control over interlayer distance. Using a molecular spacer via spin coating, we demonstrate controllable spacer thickness in a bilayer with 25% absorptance while increasing photoluminescence thanks to doping. Finally, we exploit the atomic layer deposition of alumina spacers to boost the absorptance to 31% for a 4-monolayer superlattice. Our results demonstrate that monolayer superlattices are a powerful platform directly applicable to improve strong light-matter coupling and enhance the performance of nanophotonic devices such as modulators and photodetectors.