Special Fiber Research Articles

Mode manipulation in a ring–core fiber for OAM monitoring and conversion

Abstract The monitoring and conversion of photonic orbital angular momentum (OAM) play fundamental and important roles for both classic and quantum technologies, especially in low-loss transmission media such as ring-core fibers (RCFs), which make many OAM applications practical or vastly more flexible. However, in a RCF, the modes associated with different OAM states are highly overlapping due to the circular refractive index distribution structure, which makes it difficult to distinguish and monitor the OAM modes and in turn limits its inline conversion. Here, we report the first experimental realization of mode monitoring in a RCF using mode filters (MFs), which takes advantage of the difference in the mode adiabatic evolution and the higher-order mode cutoff conditions in tapered RCFs. Different-order OAM can be filtered using MFs with different geometric parameters, as demonstrated by the linearly polarized mode intensity. Combined the mode manipulations in RCF and single-mode fiber, the fundamental mode coupling efficiency can reach 90%, the RCF mode conversion monitoring through inline transmission spectrum evolution can be realized, and the inline fabrication of RCF grating, which couples one mode to a desired mode, can be demonstrated by the fabricating process of three long-period fiber gratings. The mode conversion efficiency between 0-order and 1, 2- or 3-order OAM modes exceeds 96%. Our work provides an efficient approach to monitor and convert OAM modes in higher-order mode supporting RCFs and even other special fibers and further promotes the improvement of the capacity of OAM transmission in RCFs.

Cascaded supercontinuum generation and rogue wave harnessing

Optical rogue waves in fiber systems always arise from soliton fission and supercontinuum generation, which are of great help to understand natural extreme events as well as to control them. Here, combined special fibers with zero dispersion points at different Raman Stokes wavelength regions were proposed to realize random lasing and to stimulate cascaded supercontinuum with improved spectral flatness. Moreover, an attempt to actively control rogue waves in supercontinuum generation through external periodical perturbation was carried out. The results show that a flat 2nd-order supercontinuum that pumped at a level of a few watts can have 3 dB bandwidth of up to 120 nm, and the chaotic output pulses can be obviously harnessed through small external perturbation, i.e., the power of externally injected light is only 1.5 % to the pump power. When external periodical perturbation of the injected light aligns to or deviates from the characteristic frequencies of the system, the probability of rogue waves can be inhibited by 1.28 % or increased by 0.49 %, indicating that the soliton behavior during supercontinuum generation can be effectively controlled. This work provides a simple and efficient way to stimulate supercontinuum and to control rogue waves in a complex system, which is also inspiring for the understanding and suppression of natural extreme events, such as ocean rogue waves etc.

Physical and Mechanical Properties of Novel Multilayer Bamboo Laminated Composites Derived from Bamboo Veneer.

Compared with wood, bamboo has a special fiber gradient structure. Bamboo fibers have attracted attention as reinforced polymer composites. This study investigated the effects of lamination and fiber volume on the physical and mechanical properties of bamboo laminated composites (BLCs). Six types of BLC were derived by parallel and cross laminating bamboo veneers with high, middle, and low fiber volumes. The results indicated that the laminated structure and fiber volume significantly influenced the BLC properties. Microstructural analysis showed that parallel lamination and low fiber volume were more conducive to resin penetration and enhanced the bonding strength. Both the bending and tensile strengths of the cross lamination were lower than those of the parallel lamination. BLCs made of veneers with high and middle fiber volumes and parallel lamination had the maximum bending and tensile strengths (145.1 and 101.53 MPa, respectively). When tested for water resistance, parallel and cross lamination inhibited expansion in the thickness (TSR, 0.56-2.14%) and width (WSR, 0.07-1.61%) directions, respectively. Laminated structures and veneers with varying fiber volume contents should be chosen according to the specific application scenarios. This study provides a reference for selecting an appropriate BLC structure and fiber volume based on application.

In-fiber optofluidic michelson interferometer for detecting small volume and low concentration chemicals with a fiber ring cavity laser

An in-fiber optofluidic Michelson interferometer fabricated by femtosecond laser micromachining technology was presented. The interferometer structure was prepared by a special optical fiber with two cores and a microchannel. One core was connected to the core of a single-mode fiber (SMF) and functioned as a sensing arm on the microchannel inner wall, the other core worked as a reference arm and was connected to the optical waveguide introduced by femtosecond laser processing. By combining with a ring cavity laser, the detection limit (DL) of the interferometer could be improved. The laser sensor presented a high linear response with a refractive index (RI) sensitivity of 1039.77 nm/RIU and the calculated DL could reach as low as 1.675 × 10 −5 RIU. Then, the sensor measured different concentrations of vitamin C in tablets in the concentration range of 0–10 mg/mL with a detection limit of 0.06 mg/mL. Due to the advantages of optofluidic structure, the volume of the detection solution could be as low as few tens of nanoliters, and the time to replace and detect the solution only took a few seconds. In addition, the laser sensor realized label-free DNA hybridization detection through surface functionalization, and could detect 1 μM target DNA solution with high specificity. This sensing device had great potential for small volume and low concentration sample detection in the biochemical field. • An in-fiber optofluidic Michelson interferometer for detecting small volume and low concentration chemicals is presented. • The interferometer structure is prepared by a special microstructured optical fiber with two cores and a microchannel. • One core is connected with the SMF core as a sensing arm on the microchannel inner wall. • The other core is connected with an optical waveguide from the SMF core as a reference arm in the cladding. • Detection limit can reach as low as 0.06 mg/mL.

Degradation of Concrete Structures in Nuclear Power Plants: A Review of the Major Causes and Possible Preventive Measures

Concrete, an integral part of a nuclear power plant (NPP), experiences degradation during their operational lifetime of the plant. In this review, the major causes of concrete degradation are extensively discussed including mechanisms that are specific to NPPs. The damage mechanism could be chemical or physical. The major causes of chemical degradation include alkali–aggregate reactions, leaching, sulfate attack, bases and acids attack, and carbonation. Physical degradation is a consequence of both environmental and mechanical factors combined. These factors are mainly elevated temperature, radiation, abrasion and erosion, salt crystallization, freeze–thaw distortions, fatigue and vibration. Additionally, steel reinforcements, prestressing steels, liner plates, and structural steel also experience degradation. The prospective areas in the structural components of the NPP where the degradation could occur are mentioned and the effective solutions to the causes of degradation are highlighted. These solutions are designed to enhance the physical and chemical characteristics of concrete. Some of the major recommendations include addition of mineral substitutes, use of low water-to-cement ratio as well as low water-to-binder ratio, use of low alkali cement, use of special aggregates and fibers, use of corrosion inhibitors, use of cathodic protection, etc. The review concludes with an overview of present methods and possible recommendations used to enhance the quality of concrete towards preventing concrete degradation and increasing the lifetime of NPPs.

Monolithic Side-Pumped Amplifier Based on an Yb-Doped Tapered-Fiber and Yielding 0.53 MW 9.3 ps Pulses

We demonstrated a simple design of a monolithic all-fiber side-coupled combiner for counter-pumped amplifiers that requires no special fiber processing systems for fabrication. The combiner based on a Yb-doped polarization-maintained tapered fiber with an output core diameter of 40 µm and a total length of 1.8 m exhibiting over 60% coupling efficiency of 976 nm 0.10 NA pump power was demonstrated and utilized to amplify 1064 nm 9.3 ps 1.84 MHz pulses up to 9.1 W of average power and 0.53 MW of peak power with near diffraction-limited beam quality. The demonstrated approach seems promising for further power scaling, retaining good output beam characteristics via design optimization.

Local models for Galois deformation rings and applications

We construct projective varieties in mixed characteristic whose singularities model, in generic cases, those of tamely potentially crystalline Galois deformation rings for unramified extensions of \(\mathbb {Q}_p\) with small regular Hodge–Tate weights. We establish several significant facts about their geometry including a unibranch property at special points and a representation theoretic description of the irreducible components of their special fibers. We derive from these geometric results a number of local and global consequences: the Breuil–Mézard conjecture in arbitrary dimension for tamely potentially crystalline deformation rings with small Hodge–Tate weights (with appropriate genericity conditions), the weight part of Serre’s conjecture for U(n) as formulated by Herzig (for global Galois representations which satisfy the Taylor–Wiles hypotheses and are sufficiently generic at p), and an unconditional formulation of the weight part of Serre’s conjecture for wildly ramified representations.

A note on hyperelliptic curves with ordinary reduction over 2-adic fields

We study a class of semistable ordinary hyperelliptic curves over 2-adic fields and the special fibre of their minimal regular model. We show that these curves can be controlled using ‘cluster pictures’, similarly to the case of odd residue characteristic.

Weakly guiding graded-index ring-core fiber supporting 16-channel long distance mode division multiplexing systems based on OAM modes with low MIMO-DSP complexity.

We propose a weakly guiding graded-index ring-core fiber (RCF) with trench-assisted structure. The simulation analysis indicates that such a special fiber design is able to support 8 orbital angular momentum (OAM) mode groups (MGs) with low inter-group crosstalk (< -25 dB/km) and low intra-group differential mode delay (DMD) (< 125 ps/km) for higher order OAM MGs with topological charge |l| = 4, 5, 6, 7. The designed RCF also shows favorable tolerance characteristics to ellipticity and bending. Moreover, stable and distinguished broadband performance of proposed RCF is verified over the whole C band ranging from 1530 nm to 1565 nm. This kind of fiber design could be employed in small-scale multiple-input multiple-output digital signal processing (MIMO-DSP) intra-group modes multiplexing transmission combined with MIMO-free inter-group mode multiplexing transmission. The simulated results of the designed RCF show its great potential of the 16-channel long-distance mode division multiplexing (MDM) transmission with low MIMO-DSP complexity.

Tight and adjusted equigenerated sequences, and the special fiber

Tight and adjusted equigenerated sequences, and the special fiber

Finite determinacy and approximation of flat maps

This paper considers the problems of finite determinacy and approximation of flat analytic maps from germs of real (resp. complex) analytic spaces to R m \mathbb {R}^m (resp. C m \mathbb {C}^m ). It is shown that the flatness of analytic maps from germs of real (resp. complex) analytic spaces whose local rings are Cohen-Macaulay is finitely determined. Further, it is shown that flat maps from complete intersection (resp. Cohen-Macaulay) analytic germs can be approximated arbitrarily well by polynomial (resp. Nash) maps in such a way that the Hilbert-Samuel function of the special fibre is preserved. It is also proved that in the complex case the preservation of the Hilbert-Samuel function implies the preservation of Whitney’s tangent cone.

Co-blow-spinning of two-phase liquid to build Bead-Curtain fiber substructure for oil adsorption

The development of oil sorbents with special substructure, high adsorption capacity, reusability and good mechanical properties is of great significance for dealing with frequent maritime oil spill incidents and industrial oil-containing wastewater emission. In this work, the polystyrene (PS)/ polyvinylidene fluoride (PVDF) composite fibrous sponges with high oil adsorption capacity were fabricated by constructing a two-phase dispersion system from the microscopic perspective in fiber forming process used co-blow-spinning method. The special Bead-Curtain fiber substructure was obtained due to the difference in the stretching process of the PS and PVDF solution with different viscosity. The precursor solution of the PS/PVDF composite fibrous sponge with PVDF concentration of 20 % (SF2) increased to 79 mPa·s attributed to the addition of PVDF. The SF2 exhibited a high specific surface area (43.418 m2/g), total pore volume (0.4348 cm3/g) and adsorption capacity for various organic solvents (especially up to 279 g/g for motor oil), as well as retaining 159 g/g for motor oil after 10 cycles. Moreover, the addition of PVDF enhanced the mechanical properties of the sponges, whereas the tensile strength of the SF6 sponge was 2.36 times that of the pure PS sponge. The co-blow-spinning of two-phase liquid is a novel strategy for controlling the substructure of fibers from the microscopic perspective, which provides a novel point of view in recycling marine spilled oil.

New Method for a SEM-Based Characterization of Helical-Fiber Nonwovens.

The lack of tools particularly designed for the quantification of the fiber morphology in nonwovens, especially the multi-level structured fibers, is the main reason for the limited research studies on the establishment of realistic nonwoven structure. In this study, two polymers, cellulose acetate (CA) and thermoplastic polyurethane (TPU), which have different molecular flexibility, were chosen to produce nonwovens with helical nanofibers. Focusing on the nonwovens with helical fibers, a soft package was developed to characterize fiber morphologies, including fiber orientation, helix diameter, and curvature of helix. The novelty of this study is the proposal of a method for the characterization of nanofibrous nonwovens with special fiber shape (helical fibers) which can be used for curve fibers. The characterization results for the helical-fiber nonwoven sample and the nonwoven sample with straight fibers were compared and analyzed.

Spacing-Tailored Multicore Fiber Interface for Efficient FIFO Devices

Multicore fibers (MCFs) have attracted intense attention to overcome the capacity limit of single-core optical fiber communication system. However, as indispensable connection devices between the MCF and the individual single mode fiber (SMF), fan-in and fan-out (FIFO) devices are challenging to achieve overall performance in terms of coupling efficiency, crosstalk, return loss, and device compactness. Here we develop an MCF reverse-tapering technique to increase the core-to-core spacing of the MCF and construct a spacing-tailored interface between the MCF and the normal SMF bundle. The fabricated FIFO device for the small-core MCF with narrow core-to-core spacing of 35 μm features a low average coupling loss (∼0.6 dB), extraordinarily low crosstalk (<−65 dB) and a return loss (<−60 dB) without using any bridge elements, where the remarkably low crosstalk is about 20 dB lower than using special bridge fibers for the same type of MCF. The flexibility of reverse tapering of MCFs can overcome its intrinsic integration challenge and provide a powerful approach to constructing all-fiber FIFO devices with compact construction and excellent overall performance.

Fiber-Bragg-Grating-Based Displacement Sensors: Review of Recent Advances.

With the development of fiber optical technologies, fiber Bragg grating (FBG) sensors are frequently utilized in structural health monitoring due to their considerable advantages, including fast response, electrical passivity, corrosion resistance, multi-point sensing capability and low-cost production, as well as high accuracy and resolution over a long period. These characteristics allow FBG to be a proper alternative sensing element for displacement measurements. In this article, the recent sensing advances and principles of detection of FBG-based displacement sensors are illustrated. Specifically, the latest FBG-based displacement technologies are examined from three principles of detection, i.e., wavelength, intensity and phase signal demodulation. Regarding wavelength detection methods, the problem related to the cross-sensitivity can significantly be reduced depending on the new type of cantilever–FBG-based sensing developed. Vice versa, only the packaging method of FBG prestressed between two fixed ends can still avoid the chirp phenomenon in the reflection spectrum. Moreover, to attenuate the influence of temperature variations on the accuracy of FBG displacement sensors, specific temperature self-compensation structures were successfully designed according to the concepts of phase signal demodulation. In future investigations, different elastic structures and gratings manufactured through special fibers and new methodologies for temperature compensation will still highly refine the efficiency of FBG-based displacement sensors.

Specialization for the pro-étale fundamental group

For a formal scheme$\mathfrak {X}$of finite type over a complete rank-one valuation ring, we construct a specialization morphism\[ \pi^{\mathrm{dJ}}_1(\mathfrak{X}_\eta) \to \pi^{{\textrm{pro}}\unicode{x00E9}{\textrm{t}}}_1(\mathfrak{X}_k) \]from the de Jong fundamental group of the rigid generic fiber to the Bhatt–Scholze pro-étale fundamental group of the special fiber. The construction relies on an interplay between admissible blowups of$\mathfrak {X}$and normalizations of the irreducible components of$\mathfrak {X}_k$, and employs the Berthelot tubes of these irreducible components in an essential way. Using related techniques, we show that under certain smoothness and semistability assumptions, covering spaces in the sense of de Jong of a smooth rigid space which are tame satisfy étale descent.

Normal surface singularities with an integral homology sphere link related to space monomial curves with a plane semigroup

In this article, we consider an infinite family of normal surface singularities with an integral homology sphere link which is related to the family of space monomial curves with a plane semigroup. These monomial curves appear as the special fibers of equisingular families of curves whose generic fibers are a complex plane branch, and the related surface singularities appear in a proof of the monodromy conjecture for these curves. To investigate whether the link of a normal surface singularity is an integral homology sphere, one can use a characterization that depends on the determinant of the intersection matrix of a (partial) resolution. To study our family, we apply this characterization with a partial toric resolution of our singularities constructed as a sequence of weighted blow-ups.

Wonderful asymptotics of matrix coefficient D-modules

Beilinson–Bernstein localization realizes representations of complex reductive Lie algebras as monodromic D-modules on the “basic affine space” G/N, a torus bundle over the flag variety. A doubled version of the same space appears as the horocycle space describing the geometry of the reductive group G at infinity, near the closed stratum of the wonderful compactification G‾, or equivalently in the special fiber of the Vinberg semigroup of G. We show that Beilinson–Bernstein localization for Ug-bimodules arises naturally as the specialization at infinity in G‾ of the D-modules on G describing matrix coefficients of Lie algebra representations. More generally, the asymptotics of matrix coefficient D-modules along any stratum of G‾ are given by the matrix coefficient D-modules for parabolic restrictions. This provides a simple algebraic derivation of the relation between growth of matrix coefficients of admissible representations and n-homology. The result is an elementary consequence of the compatibility of localization with the degeneration of affine G-varieties to their asymptotic cones; analogous results hold for the asymptotics of the equations describing spherical functions on symmetric spaces.

Integrity of the Left Arcuate Fasciculus Segments Significantly Affects Language Performance in Individuals with Acute/Subacute Post-Stroke Aphasia: A Cross-Sectional Diffusion Tensor Imaging Study.

Objective: To investigate the correlation between the left arcuate fasciculus (AF) segments and acute/subacute post-stroke aphasia (PSA). Methods: Twenty-six patients underwent language assessment and MRI scanning. The integrity of the AF based on a three-segment model was evaluated using diffusion tensor imaging. All patients were classified into three groups according to the reconstruction of the left AF: completely reconstructed (group A, 8 cases), non-reconstructed (group B, 6 cases), and partially reconstructed (group C, 12 cases). The correlations and intergroup differences in language performance and diffusion indices were comprehensively estimated. Results: A correlation analyses showed that the lesion load of the language areas and diffusion indices on the left AF posterior and long segments was significantly related to some language subsets, respectively. When controlled lesion load was variable, significant correlations between diffusion indices on the posterior and long segments and comprehension, repetition, naming, and aphasia quotient were retained. Multiple comparison tests revealed intergroup differences in diffusion indices on the left AF posterior and long segments, as well as these language subsets. No significant correlation was found between the anterior segment and language performance. Conclusions: The integrity of the left AF segments, particularly the posterior segment, is crucial for the residual comprehension and repetition abilities in individuals with acute/subacute PSA, and lesion load in cortical language areas is an important factor that should be taken into account when illustrating the contributions of damage to special fiber tracts to language impairments.

Highly Sensitive Imaging Spectrometer System Based on Areal Array to Linear Array Optical Fiber Probe for Biological Spectral Detection

Noninvasive bio-molecular spectral sensing method for scattered tissue can be utilized to accurately obtain and analyze bio-molecular information. Propagation of light in biological tissues will gradually present diffusive feature and results in severe attenuation of detection light intensity and deteriorating the signal-to-noise ratio of detection system. In our work, we built a three-channel imaging spectrometer system and designed a compatible special fiber bundle probe for diffusive spectral detection. The system can synchronously collect the spectral signals from 270 fibers in the fiber bundles then convert them into electrical signal. Aiming at the aberration in the system, we also designed a corresponding data processing method to effectively realize the wavelength calibration of spectral signals. Finally, the system was applied to the nondestructive detection of human tissues and mouse with the <inline-formula> <tex-math notation="LaTeX">$15 ~ \mu \text{W}$ </tex-math></inline-formula> white light and 4.05 mw 405 nm laser. For the above extremely weak excitation light source, our system can still obtain the high signal-to-noise ratio diffusive spectra with less than 1 s integration time. Experiments were conducted to obtain spectra of back-scattering and autofluorescence of biological tissue. Experimental results show that the system has certain advantages in biological tissue scattering spectroscopy detection and autofluorescence detection.