Bending Loss Research Articles

Anticrossing and Mode Coupling in Bent All-Glass Leakage Channel Microstructured Optical Fibers with Large Mode Area

This paper presents the results of a detailed theoretical study of the bending properties of original all-glass leakage channel microstructured optical fibers (LC MOFs) over a bending radius range from 3 cm to 11 cm. These LC MOFs contain two layers of fluorine-doped silica glass elements with reduced refractive index, different diameters, and different distances between them. We determined the spatial distributions of the electric field components of different modes in addition to the usual parameters such as effective refractive indices, bending losses, and spatial intensity distributions. A detailed analysis showed that three modes for each polarization have to be considered to correctly calculate the bending losses. Two pairs of these three modes couple in two distinct bending radius ranges, specifically near 3.68 cm and near 5.95 cm, and the mode coupling in these pairs is resonant. The resulting bending losses of the LC MOF for two polarizations are very close to each other and have two maxima at bending radii of 3.68 cm and 5.95 cm. However, the nature of these maxima is not resonant; they are caused by the combined influence of all three modes, each of which has specific dependencies of losses and other parameters on the bending radius that exhibit quasi-resonant behavior near the corresponding bending radii.

PTFE-Based Circular Terahertz Dielectric Waveguides

This paper presents the transmission characteristics of flexible solid circular dielectric waveguides in the terahertz frequency band. In this paper, we measured the electrical properties of certain polymers within 325–500 GHz. Through simulation and measurement, the transmission loss, bending loss, and electric field distribution of solid-core polymer dielectric waveguides were analyzed and discussed. Additionally, we considered the surrounding cladding of the dielectric waveguide, the signal-feeding mode transmitter, and the interconnection of the dielectric waveguide. Ultimately, in the operating frequency range of 325–500 GHz, we selected PTFE rods with diameters of 0.5 mm and 1 mm as the dielectric waveguides, with measured transmission loss of less than 30 dB/m and 33 dB/m, respectively, and bending loss of less than 1 dB/m. The described dielectric waveguide has engineering significance for short-distance connections in complex geometric environments and provides a reference for subsequent research.

Coupled mode theory-based analytical model of a ring resonator refractive index sensor incorporating bending loss and dispersion

This paper presents an analytical model of a silicon nitride-based 2D ring resonator refractive index (RI) sensor using coupled mode theory (CMT). The proposed model decomposes the ring resonator into two coupling regions and employs coupled-mode equations to describe input and output amplitudes via scattering matrix analysis. The proposed sensor, operating with varying refractive indices in the background cladding, demonstrates a sensitivity of 218 nm/RIU and a total quality factor of 1198. A comprehensive analysis of the bending loss in the proposed sensor is conducted, elucidating its impact on sensitivity, coupling quality factor, and intrinsic quality factor. This analysis aids in the selection of optimal ring resonator parameters, including radius, width, and gap, to achieve superior sensing performance. Furthermore, the paper examines the effect of dispersion on sensitivity and quality and compares the results with those obtained from CMT-based silicon core ring resonator and disk resonator RI sensors. This study provides valuable insights for the design and optimization of high-performance silicon nitride-based RI sensors for various applications.

Modeling Study of Si3N4 Waveguides on a Sapphire Platform for Photonic Integration Applications.

Sapphire has various applications in photonics due to its broadband transparency, high-contrast index, and chemical and physical stability. Photonics integration on the sapphire platform has been proposed, along with potentially high-performance lasers made of group III-V materials. In parallel with developing active devices for photonics integration applications, in this work, silicon nitride optical waveguides on a sapphire substrate were analyzed using the commercial software Comsol Multiphysics in a spectral window of 800~2400 nm, covering the operating wavelengths of III-V lasers, which could be monolithically or hybridly integrated on the same substrate. A high confinement factor of ~90% near the single-mode limit was obtained, and a low bending loss of ~0.01 dB was effectively achieved with the bending radius reaching 90 μm, 70 μm, and 40 μm for wavelengths of 2000 nm, 1550 nm, and 850 nm, respectively. Furthermore, the use of a pedestal structure or a SiO2 bottom cladding layer has shown potential to further reduce bending losses. The introduction of a SiO2 bottom cladding layer effectively eliminates the influence of the substrate's larger refractive index, resulting in further improvement in waveguide performance. The platform enables tightly built waveguides and small bending radii with high field confinement and low propagation losses, showcasing silicon nitride waveguides on sapphire as promising passive components for the development of high-performance and cost-effective PICs.

Design of hollow-core anti-resonant optical fiber based on bragg elements with low-loss and wide bandwidth

A type of anti-resonant hollow-core optical fiber consisting of Bragg elements is proposed. The confinement and bending losses are numerically simulated using the finite element method. It is found that the introduction of concentric rings to form anti-resonant structure can reduce the mode transmission loss by 2 ∼ 4 orders of magnitude compared with the anti-resonant element composed of only one dielectric layer, therefore it can achieve ultra-low loss optical transmission. The influence of the structural parameters on the confinement loss was investigated. Furthermore, it is demonstrated that each dielectric layer independently contributes to the confinement of the core modes. It is also found that the Bragg reflection structure can effectively suppress the coupling between core and cladding modes, and achieve broadband low-loss optical transmission under small bending radius. In particular, it can achieve a low transmission loss of less than 0.1 dB km−1 over a wide wavelength range of 600 nm at the bending radius of 3 cm.

Bend-Net: Bending Loss Regularized Multitask Learning Network for Nuclei Segmentation in Histopathology Images

Bend-Net: Bending Loss Regularized Multitask Learning Network for Nuclei Segmentation in Histopathology Images

Design and theoretical analysis of broadband bend-resistant low-loss hollow-core anti-resonant fiber

With the development of modern fiber-optic communication technology, bend-resistant low-loss fiber within the S+C+L bands is essential to meeting the requirements of dense wavelength division multiplexing (DWDM) systems, and a small-tube-added multi-nested hollow-core anti-resonant fiber (SM-HC-ARF) is proposed. In conventional double-nested HC-ARF, a pair of circular tubes are tangent to both the inner and outer tubes to form a multi-nested structure. A small tube is put in the gap between the nested structure to enhance the anti-resonance effect further. The influence of fiber structural parameters on transmission characteristics is analyzed by the finite element method combined with the perfect matching layer condition. The numerical results show that, in the range of 1460–1625 nm, the bending loss and the confinement loss are less than 1.17 (at a bending radius of 8 cm) and 0.80 dB/km, respectively. Specifically, at 1550 nm, the bending loss is 0.43 dB/km, and the confinement loss is 0.33 dB/km. The broadband anti-bending low-loss SM-HC-ARF can be expected to apply in the DWDM system and other optical communication technologies.

Theoretical Analysis and Fabrication of a Nested Antiresonant Hollow-Core Fiber With low Tight Bend Loss

Theoretical Analysis and Fabrication of a Nested Antiresonant Hollow-Core Fiber With low Tight Bend Loss

Low loss fiber-coupled volumetric interconnects fabricated via direct laser writing

Photonic integrated circuits (PICs) are vital for high-speed data transmission. However, optical routing is limited in PICs composed of only one or a few stacked planes. Further, coupling losses must be low in deployed systems. Previously, we developed the subsurface controllable refractive index via beam exposure (SCRIBE) technique to write accurate 3D gradient refractive index (GRIN) profiles within a mesoporous silica scaffold. Here, we apply SCRIBE to fabricate low loss, broadband, polarization insensitive, fiber-coupled, single-mode volumetric interconnects that include waveguides traversing arbitrary 3D paths. By seamlessly integrating mode-matching subsurface lenses and GRIN waveguide tapers, calibrating for positional writing errors, implementing multipass exposure, automating alignment, and switching to antireflection coated fibers, we reduced the insertion loss for a fiber-PIC-fiber interconnect from 50 to 2.14 dB, or 1.47 dB, excluding the fiber array’s loss. Further, we establish an upper bound of 0.45 dB loss per coupler. We report quality factors of 27,000 and 77,000 and bending losses of 6 and 3 dB/cm for 15 and 30 µm radii microrings, respectively. We also demonstrate Bézier escalators, polarization-rotating and polarization-splitting interconnects, and a seven-channel 25 µm pitch volumetric interconnect. The SCRIBE platform presents a clear path toward realizing 3D PICs with unique functionality.

Deep Learning-Based Simultaneous Temperature- and Curvature-Sensitive Scatterplot Recognition.

Since light propagation in a multimode fiber (MMF) exhibits visually random and complex scattering patterns due to external interference, this study numerically models temperature and curvature through the finite element method in order to understand the complex interactions between the inputs and outputs of an optical fiber under conditions of temperature and curvature interference. The systematic analysis of the fiber's refractive index and bending loss characteristics determined its critical bending radius to be 15 mm. The temperature speckle atlas is plotted to reflect varying bending radii. An optimal end-to-end residual neural network model capable of automatically extracting highly similar scattering features is proposed and validated for the purpose of identifying temperature and curvature scattering maps of MMFs. The viability of the proposed scheme is tested through numerical simulations and experiments, the results of which demonstrate the effectiveness and robustness of the optimized network model.

Anti-Resonant Hollow-Core Fibers with High Birefringence and Low Loss for Terahertz Propagation

A new type of anti-resonant hollow-core fiber for terahertz waveguides is proposed. By introducing central support pillars and an elliptical structure, the fiber achieves high birefringence while maintaining low confinement loss and low material absorption loss. The fiber structure is optimized through simulation using the finite element method. The optimized fiber exhibits a birefringence of up to 1.22 × 10−2 at a frequency of 1 THz, with a confinement loss of 8.34 × 10−6 dB/cm and a material absorption loss of 7.17 × 10−3 dB/cm. Furthermore, when the bending radius of the fiber is greater than 12 cm, the bending loss of the anti-resonant optical fiber at 1 THz is less than 1.36 × 10−4 dB/cm, demonstrating good bending resistance and high practical value. It is expected to play a significant role in optical communication systems.

Concentric circular stress region-assisted pseudo-elliptical-ring-core polarization-maintaining few-mode fiber

In this paper, a pseudo-elliptical-ring-core polarization-maintaining few-mode fiber structure assisted by concentric circular stress-applying region is proposed. Numerical simulation results show that the structure can stably support 14 transmission modes. By introducing two elliptical stress regions with low refractive index inside the core, and a circular stress region with concentric core between the fiber core and cladding, the effective refractive index difference between higher-order modes is significantly improved. In the C + L band, the minimum refractive index difference between adjacent modes is not less than 2 × 10−4. At 1550 nm, the effective refractive index difference between the two fundamental modes reaches 4.8 × 10−4. The mode dispersions are less than |-33| ps/nm/km, and the maximum bending loss is in the order of 10−7 dB/m (bending radius ≥2.5 cm). This work may pave the way for the development of short-distance large-capacity optical fibers.

High-performance electro-optic switches with compact multimode interference and Bezier S-bend waveguides

High-speed and energy-efficient electro-optic (EO) switches are crucial for next-generation data communication systems. This paper presents a novel EO switch utilizing a multimode interference (MMI) coupler-based approach on a lithium-niobate (LiNbO3) platform. The switch is designed with Bezier S-bend waveguides, leading to a significant reduction in bending loss to 0.18 dB. This Bezier-bend EO switch shows an excess loss of 0.33 dB and crosstalk of −20.44 dB for the bar port switching, while the cross port switching exhibits an excess loss of 0.64 dB and crosstalk of −13.66 dB. Applying a 3.27 V voltage achieves a balanced splitting ratio of 29:29:29 between the three outputs. The length of this EO switch is 4.09 mm, which requires 4.1 V to create a phase shift, showing a voltage efficiency of 1.68 V.cm. This paper presents a promising pathway for a novel EO switch design and introduces improved signal management for next-generation computing systems.

Investigation of Frequency-Dependent Characteristics of Wire Rope under Tension Based on Transfer Function Method

Wire rope is a complex structure made by twisting wires of various sizes in the longitudinal direction. It is used to support or move engineering structures and is subject to various tensions. Dynamic properties are important parameters to evaluate the resistance to bending deformation and vibration reduction of various structures. They are affected by the magnitude of tension. In this study, an experimental method for measuring the frequency-dependent characteristics of wire rope under tension is proposed. The study analyzed flexural wave propagation employing a vibration transfer function. Experimental results showed that the transfer function of wire rope under tension is affected by tension and bending stiffness. The Newton–Raphson method was employed to numerically measure wavenumbers of the wire rope. The bending stiffness and loss factor were determined from the wavenumbers. Changes in the bending stiffness and loss factor as the tension increased were explained by the dynamic behavior of the structure under tension. As the tension increased, the bending stiffness increased, and the loss factor decreased. Hysteresis analysis indicated that the energy dissipation of wire rope is greater than that of a steel beam due to the friction between the wires. Statistical analysis confirmed a significant correlation between dynamic characteristics and tension in wire rope.

Computational investigation of transportation and thermal characteristics in a bi-modal slurry flow through a horizontally placed pipe bend

In this study, we develop a three-dimensional computational model to explore the transportation and thermal characteristics of a bi-modal slurry flowing through a horizontally placed 90° pipe bend. The slurry comprises silica sand (SS) and fly ash (FA) granular, with varying combinations (65:35, 75:25, 85:15, 95:05, and 100:0). The computational investigation has been carried out for different carrier fluid's characteristics, including Prandtl number, and flow velocity (5 m/s), for efflux concentrations of Cw = 40–60% for each mixture. Validated with experimental data, the computational approach employs a two-phase Eulerian-Eulerian RNG k-ε turbulence model and the kinetic theory of granular flow. Results reveal that the 65:35 combination exhibits minimal pressure drop, and the 100:0 combination shows maximum heat transfer characteristics, particularly with low-viscosity fluid (Pr = 2.88) and high particle efflux concentration (Cw = 60%). The study also examines bend loss coefficients (Kt), concentration distribution, convective heat transfer coefficient (h), and Nusselt number (Nu) across different Prandtl fluids and efflux concentrations.

Flow features of a horseshoe tunnel bend

Previous research on bend flow has mainly focused on rectangular channels or circular conduits with small bend radii. This study investigates the dynamics of bend flow in an unexplored geometry: the horseshoe cross-section with large bend radii, a typical configuration in hydraulic tunnels. We examine two critical flow features, energy losses and superelevation, employing theoretical equations and dimensional analysis based on experimental data collected on a physical model of a diversion tunnel. The findings reveal an exponential decrease in the bend loss coefficient with increasing Reynolds numbers and shockwaves within the bend for Froude numbers exceeding 1.945. These findings are relevant in a hydraulic tunnel design with similar features and offer insights to minimize energy losses and maintain stable flow conditions.

Waveguides for neurostimulation in the cochlea

IntroductionOptical stimulation has been suggested for neural stimulation to improve cochlear implants. Light allows for more spatially selective activation of neuron populations than electrical current, offering more independent frequency bands along the spiral ganglion. These bands are available to encode acoustic information with anticipated better frequency resolution, improving cochlear implant user performance in noisy listening environments, tonal languages, and music perception.MethodsOptical cochlear implants (oCIs) can deliver light either directly via small emitters within the cochlea or via waveguides from external optical sources. We investigated three waveguide designs made from OrmoComp®, a polymer that cures through ultraviolet (UV) radiation. Waveguides were fabricated via injection molding and coated using dip-coating or thermal reflow, or through aspiration of OrmoComp® into polyimide tubing that served as the cladding of the waveguide. The choice of fabrication technique directly determined the waveguides' total diameter: thermal reflow yielded ≈940 μm, dip-coating produced ≈306 μm, and aspiration resulted in ≈132 μm core diameter waveguides. Given the human cochlea's small size, we focused on analyzing the 306-μm and 132-μm waveguides, evaluating their optical performance (propagation and bending losses) and mechanical properties (bending stiffness and insertion forces). Furthermore, we evaluated some of these designs in in-vivo guinea pigs experiments.ResultsFor the 100-μm core diameter waveguides, the propagation losses were 12.34 ± 1.26, 1.18 ± 0.88, 1.49 ± 0.58, and 3.43 ± 0.68 dB/cm at 534, 1,375, 1,460, and 1,550 nm, respectively. The respective bending losses at a 2 mm radius of curvature were 5.50 ± 1.32, 0.56 ± 0.26, 0.79 ± 0.18, and 0.64 ± 0.23 dB, and at 1 mm 8.54 ± 1.30, 2.05 ± 0.84, 2.11 ± 0.50, and 1.44 ± 0.37 dB. The bending stiffness of a 1 mm segment of the 100-μm-diameter waveguides was 18.9 ± 2.2 N/m. Insertion forces for the 100-μm-diameter waveguides into an acrylic human-size scala tympani model were < 25 mN. For the waveguides with 306 and 940 μm total diameter, the propagation losses ranged between 0.43 and 2.40 dB/cm at 534, 680, 1,375, and 1,550 nm, between 2.19 and 3.78 dB/cm at 450 and 1,460 nm. Bending losses for 360 degrees at 1,375 nm were 5.0, 2.4, and 0.46 for a bending radius of 2.5-, 3-, and 4-mm.DiscussionOur study demonstrated that the polymer OrmoComp® is suitable for fabricating waveguides to transmit near-infrared radiation. In-vivo experiments showed optically evoked auditory responses originating from optical stimulation in the guinea pigs' first cochlear turn while radiation was delivered. Incoming experiments will focus on evaluating long-term performance of these waveguides in guinea pigs and cats. This study will be designed to provide insights into the waveguides' performance and biocompatibility over extended periods, essential for their potential clinical application in future oCIs.

Development of a smart artificial muscle using optical fibres

A McKibben artificial muscle is a fluid-driven soft actuator comprising sleeve fibres and rubber tube. However, as typical bulky and rigid displacement sensors are unsuitable as sensor elements in soft actuators, displacement sensing is challenging for the McKibben artificial muscle. Therefore, we propose an optical fibre-based smart artificial muscle (OSAM) to estimate self-displacement from the bending loss of the optical fibre used as the sleeve fibre. The optical fibre can be effortlessly integrated into the OSAM sleeve using a braiding machine, which is generally used for manufacturing strings, easing the mass production process. The radius of curvature of the optical fibre changed when the OSAM was driven. The displacement of the artificial muscle was estimated based on the sensor output. To demonstrate the usefulness of OSAM, displacement feedback control experiments were conducted using the optical fibre sensor integrated into OSAM. From the results, OSAM’s displacement showed a good response to the target displacement. Therefore, the developed artificial muscle can facilitate displacement feedback control without requiring external sensors, which in turn can improve the performance of rehabilitation and wearable devices.

High performance polarizer on thin-film lithium niobate with width-tapered Euler bending.

In this Letter, we propose and demonstrate an integrated polarizer on thin film lithium niobate (TFLN). The polarizer consists of a width-tapered 180° Euler bending waveguide featuring thin thickness and bilevel mode convertors with silica cladding. Notably, the TE0 mode is efficiently confined in the waveguide, while the TM0 mode confronts significant bending losses. The measurements reveal that the excess loss remains below 1.5 dB, and the extinction ratio surpasses 19 dB within a working bandwidth spanning from 1480 to 1578 nm. The proposed polarizer holds considerable promise for enhancing polarization handling within TFLN photonic circuits.

Research on hollow-core terahertz fiber based on Bragg anti-resonant elements arranged in a hexagonal structure

A hollow-core terahertz fiber composed of Bragg anti-resonant elements in a hexagonal structure is proposed. The function of Bragg elements on the transmission losses and bending losses of the hollow-core terahertz fiber is investigated using finite element method. Numerical simulations demonstrate that the introduction of Bragg elements for the anti-resonant cladding can significantly reduce the confinement losses of the fiber, the appropriate choice of the outer cladding diameter can also contribute to the reduction of the total loss. The bending loss shows low dependence on the bending angle for the proposed fiber with the Bragg elements. Compared with the anti-resonant hollow-core terahertz fiber composed of only a single dielectric layer, the bending losses of the hollow-core terahertz fiber with the Bragg elements can be reduced by more than an order of magnitude.