Core Mode Research Articles

Fourfold truncated double-nested antiresonant hollow-core fiber with ultralow loss and ultrahigh mode purity

Hollow-core fibers (HCFs) are inherently multimode, making it crucial to filter out higher-order modes (HOMs) within the shortest possible fiber length for applications such as high-speed coherent communications and fiber-optic gyroscopes. However, current HCF designs face the challenges of simultaneously achieving ultralow fundamental mode (FM) loss and ultrahigh HOM suppression. In this study, we present a fourfold truncated double-nested antiresonant nodeless hollow-core fiber (4T-DNANF) structure that addresses this challenge. Our 4T-DNANF enables greater control over phase matching between core modes and air modes in the cladding, allowing for minimized FM loss and substantially increased HOM loss. Experimentally, we fabricated several HCFs: one with an FM loss of 0.1 dB/km and an HOM loss of 430 dB/km, and another achieving an FM loss of 0.13 dB/km with a HOM loss of 6500 dB/km, yielding a higher-order mode extinction ratio of 5×104—the highest reported to date.

Constraining differential rotation in γ Doradus stars from the properties of inertial dips

The presence of dips in the gravity mode period spacing versus period diagram of γ Doradus stars is now well established thanks to recent asteroseismic studies. Such Lorentzian-shaped inertial dips arise from the interaction of gravito-inertial modes in the radiative envelope of intermediate-mass main sequence stars with pure inertial modes in their convective core, and allow us to study stellar internal properties. This window onto stellar internal dynamics is extremely valuable in the context of the understanding of angular-momentum transport inside stars, as it allows us to probe rotation in their core. We investigate the signature and the detectability of a differential rotation between the convective core and the near-core region inside γ Doradus stars from the properties of inertial dips. We studied the coupling between gravito-inertial modes in the radiative zone and pure inertial modes in the convective core in the sub-inertial regime, allowing for a two-zone differential rotation from the two sides of the core-to-envelope boundary. We solved the coupling equation numerically and matched the result to an analytical derivation of the Lorentzian dip properties. We then used typical values of measured near-core rotation and buoyancy travel time to infer ranges of parameters for which differential core to near-core rotation would be detectable in current Kepler data. We show that increasing the convective core rotation with respect to the near-core rotation leads to a shift of the period of the observed dip to lower periods. In addition, the dip gets deeper and thinner as the convective core rotation increases. We demonstrate that such a signature is detectable in Kepler data, given appropriate dip-parameter ranges and near-core structural properties. Studying the dip properties in asteroseismic data thus allows us to access core to near-core radial differential rotation and to better understand the transport of angular momentum at convective--radiative interfaces in intermediate-mass main sequence stars.

Simultaneous tri-parameter surface plasmon resonance photonic crystal fiber sensor

Abstract This study presents a photonic crystal fiber (PCF) integrated with a surface plasmon resonance (SPR) sensor that utilizes two orthogonal polarization core modes for sensing. The PCF features a thin indium tin oxide (ITO) layer on the inner channel and lower polished surface, an upper polished surface with a thin gold film, and an inner channel filled with magnetic fluid (MF) for magnetic field detection. Additionally, a temperature and refractive index sensitive material polydimethylsiloxane (PDMS) is placed on the lower polished surface, while the upper polished surface is designed for refractive index measurement. This multifunctional PCF-SPR sensor offers a compact and efficient solution for simultaneous detection of magnetic fields, temperature, and refractive index variations. The highest magnetic field sensitivity in the range of 0~12Oe is 11.1nm/Oe, the highest temperature sensitivity in the range of 20~400℃ is -0.5nm/℃, and the highest refractive index sensitivity in the range of 1.17~1.35μm is 1000nm/RIU. The designed sensor effectively mitigates the cross-sensitivity issues during concurrent measurements of the magnetic field, temperature, and refractive index simultaneously, presenting significant potential for applications in complex environment, including mineral resource exploration, geological and environmental assessments.

Uncovering the implicit dimensions of empathy in architectural design: seeing through empathy

ABSTRACT This article examines the implicit dimensions of empathy in the early architectural design process, utilizing think-aloud protocols to reveal how designers engage empathically with their creations. Grounded in early 20th-century empathy theories, phenomenological philosophy, and design cognition, we developed the ‘Feeling AS’ empathy framework, which identifies three core modes of empathy: (1) user, (2) space, and (3) movement. Analysis of design protocols demonstrates how empathy shapes design thinking, influences problem reframing, and uncovers spatial affordances tied to user embodiment. Empathy contributes to the design process in two key ways. First, it aids in problem identification, ideation, and a deep understanding of users’ needs during the conceptual stage. Second, empathy enables designers to refine design solutions by revisiting decisions and reframing problems from the users’ perspective as the process evolves. The study portrays empathy as a perceptual and reflective tool, akin to sketching, that facilitates diverse perspectives and establishes embodied connections with users and spaces. We frame this process as ‘seeing through empathy,’ encompassing empathic framing, spatial affordances, and embodiment. This research broadens the scope of empathy research to include spatial dimensions, emphasizing its inherent role and extending it beyond conscious strategies to become an embedded aspect of the creative process.

Engineering “Meso‐Atom” Bonding: Honeycomb‐Network Transitions in Reticular Liquid Crystals

ABSTRACTA library of rod‐like bolapolyphiles with sticky hydrogen‐bonded glycerol groups at their ends and having highly branched side chains with a carbosilane‐based four‐way branching point, all based on the same oligo(phenylene ethynylene) core, has been synthesized and investigated. For these compounds, a A15‐type Frank–Kasper phase is formed upon side‐chain elongation in the steric frustration range at the transition from the triangular to the much larger square honeycombs. In contrast to the previously known tetrahedral sphere packings the A15 phase is in this case formed by tetrahedral networks of aggregates of parallelly organized π‐conjugated rods. This allows the design of compounds with wide ranges of the A15 network down to room temperature. However, its formation becomes strongly disfavored by core fluorination that is attributed to a changing mode of core–core interaction that also modifies the square honeycombs by deformation of the squares into rectangular or rhombic cells, either with or without emergence of tilt of the rods.

Low-loss weakly coupled four-mode hollow-core antiresonant fiber based on centrosymmetric nested structure

Abstract This paper designs a novel centrosymmetric double-layer nested antiresonant fiber (CDNAF) with few-mode transmission characteristics. The cladding structure of the CDNAF incorporates glass plates and multilayer capillaries, effectively mitigating the coupling between various core modes and cladding modes. Simulation results show that the CDNAF can support four modes of low-loss transmission from LP01 to LP02 at 1550 nm. The confinement loss (CL) of the four modes is less than 0.008 dB/km, 0.07 dB/km, 0.42 dB/km, and 4.8 dB/km, respectively, and the CDNAF has a sizeable differential group delay (DGD) and weak bending sensitivity. The loss of high-order modes is much greater than that of the other four transmission modes, ensuring high-purity transmission of the four modes. In the wavelength range of 1200–1700 nm, the CDNAF ensures few-mode characteristics with at least two low-loss transmission modes. Furthermore, the effective refractive index difference (Δneff) between adjacent modes is much greater than 10^(-4), eliminating or significantly reducing the need for multiple-input multiple-output digital signal processing (MIMO-DSP) techniques in optical communication systems. Additionally, the results demonstrate that CDNAF can transmit three modes at an ultimate bending radius of 5 cm and can transmit four modes like a straight fiber at a bending radius of 18 cm, which demonstrates that CDNAF has excellent bending performance. These excellent characteristics give the CDNAF great potential for application in large-capacity optical communication systems.

Zero and double-knotted droplet-shaped optical fiber sensor for rapid temperature variation monitoring

Compact, simple optical fiber sensors based on a macro-bend fiber configuration were fabricated and proposed for instantaneous temperature measurement. These fiber sensors were manufactured by straightforwardly mechanically bending two different pieces of single-mode fiber (SMF) into zero-knotted droplet-shaped and double-knotted droplet-shaped, separately, with radii of a few millimeters. The sharp bending excites mode interferences among the core mode and the stimulated modes transmitting in the cladding region of the silica SMF. Many resonant interference fringes were perceived in the transmission signal and were noticed to shift to a shorter spectral region with the rise of environmental temperature (ET). The resultant data prove the practicality of the fabricated optical fiber sensors with excellent temperature sensitivities of about −1.128 nm/°C and −1.904 nm/°C, for zero-knotted droplet-shaped and double-knotted droplet-shaped, respectively, which is several times larger than sensors based on straight-transmitted fiber constructions. The proposed sensors’ structures may contribute effectively to temperature variations monitoring for environmental or industrial uses due to their large thermo-optical coefficient of the silica core and the big RI difference between the core and cladding of the bending fiber section.

Fiber Bragg Grating-Based Tunable Wavelength Orbital Angular Momentum Beam Generation with Varying Polarization

This paper introduces and theoretically analyze the generation of orbital angular momentum (OAM) modes with different polarization in a few-mode optical fiber using short-period gratings (Bragg gratings) at telecommunication wavelengths. The modal characteristics of the supported modes have been studied using a full-vector true-mode analysis. Additionally, a appropriately designed raised-cosine apodized grating is employed to couple the HE11 core mode to the counter-propagating cladding mode. In contrast to the long-period grating based OAM mode generation, the present scheme is free from periodic back-coupling of optical power into the fundamental core mode which drastically enhances the OAM mode purity. The ±1-order OAM beam has been generated by combining the first higher order core modes with a π/2 phase shift between them. This paper also shows that by combining different higher order modes, it is possible to obtain a linearly polarised OAM mode or a circularly polarised OAM mode. Finally, I also report that in fibers with larger core radius, the higher order OAM mode of topological charge ±2 or higher can also be generated using similar approach of using short-period gratings. The topological charge of the OAM mode is verified by observing both the coaxial and off axial interference fringes. Received: 13 March 2024 | Revised: 3 June 2024 | Accepted: 25 November 2024 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Avijit Koley: Conceptualization, Methodology, Software, Validation, Formal analysis, Data curation, Writing - original draft, Writing - review & editing.

The universal Rhs shell structure accommodates various toxins inside and different functional decorations on the outside

In this issue of Structure, Kielkopf etal.1 report the crystal structures of Rhs proteins that are genetically fused to the type VI secretion system PAAR or VgrG proteins. The work highlights the structural similarities of Rhs proteins despite diverse decorations surrounding the Rhs core and different delivery modes.

Femtosecond laser direct writing tilted fiber Bragg gratings in multicore fiber.

In this Letter, we propose a new method utilizing femtosecond laser direct writing technology to rapidly inscribe high-quality tilted fiber Bragg gratings (TFBGs) in multicore fibers (MCFs). A series of TFBGs with varying tilt angles were directly inscribed in MCFs using the Plane-by-Plane (Pl-by-Pl) method, and the writing time for a 4 mm long TFBG was only 3.60 s. The TFBGs couple the transmitted light from the cores of the MCF into the cladding, thereby increasing the cross talk between adjacent cores. By monitoring the wavelength and intensity changes of the core modes coupled back to the central core from the TFBGs inscribed in the edge cores, two-dimensional (2D) vector bending measurements were achieved.

Lossy Mode Resonance Optical Fiber Enhanced by Electrochemical-Molecularly Imprinted Polymers for Glucose Detection.

Noninvasive glucose sensors are emergent intelligent sensors for analyzing glucose concentration in body fluids within invasion-free conditions. Conventional glucose sensors are often limited by a number of issues such as invasive and real-time detection, creating challenges in continuously characterizing biomarkers or subtle binding dynamics. In this study, we introduce an efficient lossy mode resonance (LMR) optical fiber sensor incorporating the molecularly imprinted polymers (MIPs) to amplify glucose molecules. A molecularly imprinted recognition platform is created on an LMR sensor surface through a convenient one-step electrochemical (EC) polymerization method, in which 3-Aminophenylboric acid and glucose serve as the functional monomer and template molecule, respectively. LMR resonance wavelength shift induced by the coupling of the optical lossy mode and the fiber core mode is employed as the parameter to characterize biomolecules. Due to its high sensitivity to surrounding environment changes, a limit of detection (LOD) of 4.62 × 10-2 μmol/L for glucose can be achieved by this optical fiber sensor. Additionally, the prepared EC-MIPs LMR sensor is capable of detecting glucose molecules in human saliva samples with high accuracy, endowing its potential for practical applications.

Inscription and Thermal Stability of Fiber Bragg Gratings in Hydrogen-Loaded Optical Fibers Using a 266 nm Pulsed Laser

Fiber Bragg gratings (FBGs) have gained substantial research interest due to their exceptional sensing capabilities. Traditionally, FBG fabrication has required the use of pre-hydrogenated fibers and high-cost laser systems such as excimer lasers at 193 nm or femtosecond lasers. In this study, we present the first instance of FBG inscription in hydrogen-loaded, standard single-mode silica optical fibers using a more affordable 266 nm solid-state pulsed laser combined with a scanning phase mask lithography technique. We systematically explored the effects of pulse energy and scanning speed on the quality and spectral characteristics of the gratings, achieving reflectivities as high as 99.81%. Additionally, we tracked the spectral evolution during the FBG inscription process, demonstrating uniform growth of the core mode. We also investigated the stability of the core mode during a 24-h thermal annealing process up to 150 °C. The sensitivity was 10.7 pm/°C in the range of 0 to 130 °C. Furthermore, strain measurement was conducted based on the FBG annealed at 100 °C, showing a sensitivity of 0.943 pm/µε in the range of 0 to 1667 µε.

The Doctors, Their Patients, and the Symptom Checker App: Qualitative Interview Study With General Practitioners in Germany.

Symptom checkers are designed for laypeople and promise to provide a preliminary diagnosis, a sense of urgency, and a suggested course of action. We used the international symptom checker app (SCA) Ada App as an example to answer the following question: How do general practitioners (GPs) experience the SCA in relation to the macro, meso, and micro level of their daily work, and how does this interact with work-related psychosocial resources and demands? We conducted 8 semistructured interviews with GPs in Germany between December 2020 and February 2022. We analyzed the data using the integrative basic method, an interpretative-reconstructive method, to identify core themes and modes of thematization. Although most GPs in this study were open to digitization in health care and their practice, only one was familiar with the SCA. GPs considered the SCA as part of the "unorganized stage" of patients' searching about their conditions. Some preferred it to popular search engines. They considered it relevant to their work as soon as the SCA would influence patients' decisions to see a doctor. Some wanted to see the results of the SCA in advance in order to decide on the patient's next steps. GPs described the diagnostic process as guided by shared decision-making, with the GP taking the lead and the patient deciding. They saw diagnosis as an act of making sense of data, which the SCA would not be able to do, despite the huge amounts of data. GPs took a techno-pragmatic view of SCA. They operate in a health care system of increasing scarcity. They saw the SCA as a potential work-related resource if it helped them to reduce administrative tasks and unnecessary patient contacts. The SCA was seen as a potential work-related demand if it increased workload, for example, if it increased patients' anxiety, was too risk-averse, or made patients more insistent on their own opinions.

Numerical study of a tapered fiber magnetic field sensor based on the ENZ mode

This study introduces what we believe to be a novel magnetic field sensor that utilizes a tapered optical fiber coated with indium tin oxide (ITO) and titanium dioxide (TiO2), operating on an epsilon-near-zero (ENZ) mode. The evanescent field around the tapered optical fiber can excite the ENZ mode of the ITO film, and the TiO2 layer can ensure the phase matching between the fiber core mode and the ENZ mode. The sensor, immersed in magnetic fluid, leverages the unique properties of ENZ materials to achieve a high sensitivity and resolution in the near-infrared (NIR) region. Through a simulation, the sensor demonstrated a maximum sensitivity of 6900 nm/RIU and a magnetic field sensitivity of 370 pm/Oe. The findings suggest that ENZ mode-based optic sensing presents a promising alternative to traditional plasmonic sensing methods, offering potential applications in various fields requiring precise magnetic field measurements.

An Mach-Zehnder interferometer refractive index sensor based on self-phase modulation effect in a tapered double-cladding highly nonlinear fiber

An Mach-Zehnder interferometer (MZI) sensor based on self-phase modulation (SPM) effect in a tapered double-cladding highly nonlinear fiber (DCHNLF) was proposed and experimentally verified for refractive index (RI) measurement. The DCHNLF was tapered and the SPM spectrum generated in its untapered region acted as the broadband light source for the sensor. The integration of the SPM effect and the RI detection not only simplified the structure of the sensor, but also enhanced its long-term stability and reliability. Since the effective RI of the outer cladding mode of the tapered DCHNLF was affected by the RI variation, a spectral shift would occur in interference spectrum between the core mode and the outer cladding mode. The tapering treatment enhanced the evanescent wave on the surface of DCHNLF, making the sensor more sensitive to external RI. In the external RI range of 1.3333 ∼ 1.3972, the sensor achieved an excellent sensitivity of 238.51 nm/RIU. In addition, the effect of average pump power and pump wavelength on the sensor performance were experimentally discussed. The results showed that the sensitivity was not affected by the pump condition. This MZI RI sensor has advantages of excellent performance, simple structure and easy fabrication, demonstrating broad application prospects in biomedical research, marine environment monitoring, and human health detection.

Broadband high birefringence and single-polarization hollow-core anti-resonant fibers with an elliptical-like core

Due to the light-guiding mechanism of hollow-core anti-resonant fibers (HC-ARFs), the low overlap between core modes and anti-resonant layers poses a challenge in achieving high birefringence. To address this issue, we propose three high-birefringence HC-ARFs with an elliptical core and varying cladding compositions and conduct a detailed optimization and analysis for structure (c). Simulation results demonstrate that structure (a) and structure (b) provide high birefringence, broadband, and low-loss transmission properties. Specifically, structure (a) achieves a birefringence greater than 1.3×10−4 over a 680 nm wavelength range, and structure (b) achieves a birefringence greater than 1.6×10−4 over a 580 nm wavelength range, both maintaining fundamental mode (FM) loss below 1 dB/m. Structure (c) enhances birefringence by an order of magnitude and offers excellent single-polarization properties by introducing high-refractive-index material. At 1.55μm, structure (c) achieves a birefringence of 0.98×10−3, with a low FM loss for x-polarization of 0.01 dB/m and a polarization extinction ratio (PER) of 57450. Additionally, structure (c) exhibits low bend loss in the x-direction, with only 0.06 dB/m for a bend radius of 6 cm.

Research on Network Security Protection Technology Based on P2AEDR in New Low-Voltage Control Scenarios for Power IoT and Other Blockchain-Based IoT Architectures.

In the construction of new power systems, the traditional network security protection mainly based on boundary protection belongs to static defense and still relies mainly on manual processing in vulnerability repair, threat response, etc. It is difficult to adapt to the security protection needs in large-scale distributed new energy, third-party aggregation platforms, and flexible interaction scenarios with power grid enterprise systems. It is necessary to conduct research on dynamic security protection models for IoT and other Blockchain-based IoT architectures. This article proposes a network security comprehensive protection model P2AEDR based on different interaction modes of cloud-edge interaction and cloud-cloud interaction. Through continuous trust evaluation, dynamic access control, and other technologies, it strengthens the internal defense capabilities of power grid business, shifting from static protection as the core mode to a real-time intelligent perception and automated response mode, and ultimately achieving the goal of dynamic defense, meeting the security protection needs of large-scale controlled terminal access and third-party aggregation platforms. Meanwhile, this article proposes a dynamic trust evaluation algorithm based on deep learning, which protects the secure access and use of various resources in a more refined learning approach based on the interaction information monitored in the system. Through experimental verification of the dynamic trust evaluation algorithm, it is shown that the proposed model has good trust evaluation performance. Therefore, this research is beneficial for trustworthy Power IoT and other Blockchain-based IoT architectures.

Highly sensitive threaded LPFG strain sensor

Long Period Fiber Grating (LPFG) strain sensors have been used to monitor the structural health of bridges and buildings, and there is a need to further improve their sensing sensitivity. This article proposed a threaded LPFG strain sensor, which used a CO2 laser to etch a long groove at the top of the cladding of a single-mode fiber. The fiber in the long groove area was heated and twisted to fabricate a long period fiber grating (TH-LPFG) strain sensor with a threaded groove on the cladding. When strain is applied, the strain is concentrated in the threaded area on the cladding, increasing and decreasing the effective refractive index changes of the cladding mode and core mode respectively, achieving enhanced strain sensing. The experimental outcomes demonstrate that the TH-LPFG strain sensor achieves a sensitivity of 44.9 pm/µε to strain, while its cross-sensitivity to temperature is minimal, at just 1.28 µε/°C. TH-LPFG provides a new solution for enhancing the sensitivity of LPFG strain sensing, with low production cost and low temperature crosstalk. It can be used in the field of highly sensitive strain monitoring of building structures.

Schlieren Image Velocimetry and Modal Decomposition Study of Preheated Isothermal Flow From a Generic Multi-Swirl Burner

Abstract This study presents an experimental investigation into the turbulent flow characteristics of an unconfined counter-rotating dual swirl burner under external acoustic excitation. Utilizing Schlieren image velocimetry (SIV), we capture the velocity field of the swirling jets. Mean velocity field analysis reveals the upstream propagation of the central recirculation zone within the burner passages. Through proper orthogonal decomposition (POD) analysis on instantaneous axial velocity fields, coherent structures are identified and the impact of different actuation methods on spatial modes is illustrated. Spatial modes of the unforced (natural) flow show the presence of a single and double helical precessing vortex core (PVC) modes at St = 0.53. Low-frequency acoustic actuation (St = 0.46) effectively suppresses the PVC mode, while high-frequency (St = 2) actuation stabilizes it. Broadband excitation of the flow field, however, induces the excitation of both single and double helical PVC modes.

Sensing performance comparison for temperature and liquid level sensor based on uniform and step-Etched microfiber TFBG

By using the hydrofluoric acid uniform-etching and step-etching methods, a tilted fiber Bragg grating (TFBG) microfiber structure was fabricated, where the cladding diameter of the traditional TFBG was reduced to micrometer scale. The temperature sensing characteristics of the uniform-etched and step-etched microfiber TFBGs were experimentally studied and compared. The core mode of its transmission spectrum was used for sensing the temperature change; while the normalized area of cladding modes has been used for real-time monitoring the liquid level. The simultaneous measurement of temperature and liquid level has been experimentally demonstrated for the proposed microfiber TFBG. By combining the strong evanescent field of microfiber and the unique structural advantages of TFBG, the proposed microfiber TFBG has a great potential in developing the miniature optical fiber sensors.