Loss Of Fibers Research Articles

Generation of optical UWB signals based on combined bright solitons

We investigate the generation of ultra-wide band (UWB) signal in all optical domain based on combined bright solitons by numerical method. The combined solitons with ultra-wideband characteristics can be obtained by multiple bright solitons. The power spectrum can be modulated by pulse interval, pulse width and phase difference of combined bright solitons to satisfy with the Federal Communications Commission (FCC) spectrum mask. Meanwhile, the transmissions of combined bright solitons in single-mode fibers are discussed. The fiber loss and dispersion effects have the influence on the transmissions of combined bright solitons. In order to eliminate dispersion effects, the stable transmission of signals in dispersion decreasing fibers is proposed.

Sodium Nitroprusside Stimulation of Elastic Matrix Regeneration by Aneurysmal Smooth Muscle Cells.

The chronic overexpression of matrix metalloproteases leading to consequent degradation and loss of the elastic matrix with the reduction in tissue elasticity is central to the pathophysiology of proteolytic disorders, such as abdominal aortic aneurysms (AAAs), which are localized rupture-prone aortic expansions. Effecting tissue repair to alleviate this condition is contingent on restoring elastic matrix homeostasis in the aortic wall. This is naturally irreversible due to the poor elastogenicity of adult and diseased vascular cells, and the impaired ability to assemble mature elastic fibers, more so in the context of phenotypic changes to medial smooth muscle cells (SMCs) owing to the loss of nitric oxide (NO) signaling in the AAA wall tissue. In this study, we report the benefits of the exposure of primary human aneurysmal SMCs (aHASMCs) to NO donor drug, sodium nitroprusside (SNP), in improving extracellular matrix homeostasis, particularly aspects of elastic fiber assembly, and inhibition of proteolytic degradation. SNP treatment (100 nM) upregulated elastic matrix regeneration at both gene (p < 0.05) and protein levels (p < 0.01) without affecting cell proliferation, improved gene, and protein expression of crosslinking enzyme, lysyl oxidase (p < 0.05), inhibited the expression of MMP2 (matrix metalloprotease 2) significantly (p < 0.05) and promoted contractile SMC phenotypes in aHASMC culture. In addition, SNP also attenuated the expression of mitogen-activated protein kinases, a significant player in AAA formation and progression. Our results indicate the promise of SNP for therapeutic augmentation of elastic matrix regeneration, with prospects for wall repair in AAAs. Impact Statement Chronic and naturally irreversible enzymatic degradation and loss of elastic fibers are centric to proteolytic disorders such as abdominal aortic aneurysms (AAAs). This is linked to poor elastogenicity of adult and diseased vascular cells, compromising their ability to assemble mature elastic fibers. Toward addressing this, we demonstrate the phenotype-modulatory properties of a nitric oxide donor drug, sodium nitroprusside on aneurysmal smooth muscle cells, and its dose-specific proelastogenic and antiproteolytic properties for restoring elastic matrix homeostasis. Combined with the development of vehicles for site-localized, controlled drug delivery, this can potentially lead to a new nonsurgical approach for AAA wall repair in the future.

Targeting Epidermal Growth Factor Receptor to Stimulate Elastic Matrix Regenerative Repair.

Abdominal aortic aneurysms (AAAs) represent a multifactorial, proteolytic disorder involving disintegration of the matrix structure within the AAA wall. Intrinsic deficiency of adult vascular cells to regenerate and repair the wall elastic matrix, which contributes to vessel stretch and recoil, is a major clinical challenge to therapeutic reversal of AAA growth. In this study, we investigate the involvement of epidermal growth factor receptor-mitogen activated protein kinase (EGFR-MAPK) pathway in the activation of aneurysmal smooth muscle cells (SMCs) by neutrophil elastase, and how EGFR can be targeted for elastic matrix regeneration. We have demonstrated that neutrophil elastase activates EGFR and downregulates expression level of key elastin homeostasis genes (elastin, crosslinking enzyme-lysyl oxidase, and fibulin4) between a dose range of 1-10 μg/mL (p < 0.05). It also incites downstream proteolytic outcomes by upregulating p-extracellular signal-regulated kinase (ERK)1/2 (p < 0.0001) and matrix metalloprotease 2 (MMP2) at a protein level, which is significantly downregulated upon EGFR-specific inhibition by tyrosine kinase inhibitor AG1478 (p-ERK1/2 and MMP2 [p < 0.05]). Moreover, we have shown that EGFR inhibition suppresses collagen amounts in aneurysmal SMCs (p < 0.05) and promotes robust formation of elastic fibers by enhancing its deposition in the extracellular space. Hence, the EGFR-MAPK pathway in aneurysmal cells can be targeted to provide therapeutic effects toward stimulating vascular matrix regeneration. Impact statement Proteolytic disorders such as aortal expansions, called abdominal aortic aneurysms (AAAs), are characterized by naturally irreversible enzymatic breakdown and loss of elastic fibers, a problem that has not yet been surmounted by existing tissue engineering approaches. In this work, we show, for the first time, how epidermal growth factor receptor (EGFR) inhibition provides downstream benefits in elastic fiber assembly and deposition in aneurysmal smooth muscle cell cultures. This work can open future possibilities for development of EGFR-targeted drug-based therapies not only for vessel wall repair in AAAs but also other proteolytically compromised elastic tissues.

Artificial intelligence designer for optical Fibers: Inverse design of a Hollow-Core Anti-Resonant fiber based on a tandem neural network

In this work, artificial intelligence (AI) is trained to “study” optical fibers as an AI optical fiber scientist. The dataset is constructed on the structural parameters and confinement loss of hollow-core anti-resonant fibers and is divided into different datasets. An effective approach to overcome the non-uniqueness challenge of inverse designs is the tandem neural network (T-NN), which consists of a forward prediction model and an inverse design model, which are trained by different datasets. The impact of the hyperparameter on the performance of the proposed model is also studied. For the forward prediction model, the mean square error reaches the lowest value of 0.0007 with 6 hidden layers; the nodes of each hidden layer are 800, and the corresponding coefficient of determination R2 is 0.9154. Moreover, the R2CL of the T-NN can reach the maximum value of 0.9881 for the dataset-1-0. The comparison between the target, prediction result, and calculation result proves that the proposed approach is an effective way to design hollow-core anti-resonant fibers intelligently. Compared with current numerical simulation methods, the presented AI model based on the T-NN is more “intelligent”. This study can both accelerate the design of hollow-core anti-resonant fibers and provide guidance on the development of AI scientists in optics.

Diagnostic Accuracy of Perception Threshold Tracking in the Detection of Small Fiber Damage in Type 1 Diabetes.

An objective assessment of small nerve fibers is key to the early detection of diabetic peripheral neuropathy (DPN). This study investigates the diagnostic accuracy of a novel perception threshold tracking technique in detecting small nerve fiber damage. Participants with type 1 diabetes (T1DM) without DPN (n = 20), with DPN (n = 20), with painful DPN (n = 20) and 20 healthy controls (HCs) underwent perception threshold tracking on the foot and corneal confocal microscopy. Diagnostic accuracy of perception threshold tracking compared to corneal confocal microscopy was analyzed using logistic regression. The rheobase, corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and corneal nerve fiber length (CNFL) (all P < .001) differed between groups. The diagnostic accuracy of perception threshold tracking (rheobase) was excellent for identifying small nerve fiber damage, especially for CNFL with a sensitivity of 94%, specificity 94%, positive predictive value 97%, and negative predictive value 89%. There was a significant correlation between rheobase with CNFD, CNBD, CNFL, and Michigan Neuropathy Screening Instrument (all P < .001). Perception threshold tracking had a very high diagnostic agreement with corneal confocal microscopy for detecting small nerve fiber loss and may have clinical utility for assessing small nerve fiber damage and hence early DPN. NCT04078516.

A Nrf2-OSGIN1&2-HSP70 axis mediates cigarette smoke-induced endothelial detachment: implications for plaque erosion.

Endothelial erosion of plaques is responsible for ∼30% of acute coronary syndromes (ACS). Smoking is a risk factor for plaque erosion, which most frequently occurs on the upstream surface of plaques where the endothelium experiences elevated shear stress. We sought to recreate these conditions in vitro to identify potential pathological mechanisms that might be of relevance to plaque erosion. Culturing human coronary artery endothelial cells (HCAECs) under elevated flow (shear stress of 7.5 Pa) and chronically exposing them to cigarette smoke extract (CSE) and tumour necrosis factor-alpha (TNFα) recapitulated a defect in HCAEC adhesion, which corresponded with augmented Nrf2-regulated gene expression. Pharmacological activation or adenoviral overexpression of Nrf2 triggered endothelial detachment, identifying Nrf2 as a mediator of endothelial detachment. Growth/Differentiation Factor-15 (GDF15) expression was elevated in this model, with protein expression elevated in the plasma of patients experiencing plaque erosion compared with plaque rupture. The expression of two Nrf2-regulated genes, OSGIN1 and OSGIN2, was increased by CSE and TNFα under elevated flow and was also elevated in the aortas of mice exposed to cigarette smoke in vivo. Knockdown of OSGIN1&2 inhibited Nrf2-induced cell detachment. Overexpression of OSGIN1&2 induced endothelial detachment and resulted in cell cycle arrest, induction of senescence, loss of focal adhesions and actin stress fibres, and disturbed proteostasis mediated in part by HSP70, restoration of which reduced HCAEC detachment. In ACS patients who smoked, blood concentrations of HSP70 were elevated in plaque erosion compared with plaque rupture. We identified a novel Nrf2-OSGIN1&2-HSP70 axis that regulates endothelial adhesion, elevated GDF15 and HSP70 as biomarkers for plaque erosion in patients who smoke, and two therapeutic targets that offer the potential for reducing the risk of plaque erosion.

Corneal nerve loss and increased Langerhans cells are associated with disease severity in patients with rheumatoid arthritis.

Rheumatoid arthritis (RA) is a multisystem autoimmune disorder characterized by articular and extra-articular manifestations. Neuropathy is a poorly studied manifestation of RA. The aim of this study was to utilize the rapid non-invasive ophthalmic imaging technique of corneal confocal microscopy to identify whether there is evidence of small nerve fibre injury and immune cell activation in patients with RA. Fifty consecutive patients with RA and 35 healthy control participants were enrolled in this single-centre, cross-sectional study conducted at a university hospital. Disease activity was assessed with the 28-Joint Disease Activity Score and erythrocyte sedimentation rate (DAS28-ESR). Central corneal sensitivity was measured with a Cochet-Bonnet contact corneal esthesiometer. A laser scanning in vivo corneal confocal microscope was used to quantify corneal nerve fibre density (CNFD), nerve branch density (CNBD), nerve fibre length (CNFL), and Langerhans cell (LC) density. Corneal sensitivity (P = 0.01), CNFD (P = 0.02), CNBD (P < 0.001), and CNFL (P < 0.001) were lower, and mature (P = 0.001) and immature LC densities (P = 0.011) were higher in patients with RA compared to control subjects. CNFD (P = 0.016) and CNFL (P = 0.028) were significantly lower in patients with moderate to high (DAS28-ESR > 3.2) compared to mild (DAS28-ESR ≤ 3.2) disease activity. Furthermore, the DAS28-ESR score correlated with CNFD (r = -0.425; P = 0.002), CNBD (ρ = -0.362; P = 0.010), CNFL (r = -0.464; P = 0.001), total LC density (ρ = 0.362; P = 0.010) and immature LC density (ρ = 0.343; P = 0.015). This study demonstrates reduced corneal sensitivity, corneal nerve fibre loss and increased LCs which were associated with the severity of disease activity in patients with RA.

Comparison of meat quality and glycolysis potential of two hybrid pigs in three-way hybrid model.

With the improvement of consumers' requirements for pork quality, the method of crossbreeding with excellent local pig breeds to improve meat quality is popular. Saba pig has high reproduction rate, good meat quality and high utilization rate of roughage, but its excellent characteristics have not been fully developed and utilized. To promote the development and utilization of Saba pigs and production of high-quality pork, the meat quality traits and glycolysis potential of Duroc × (Landrace × Yorkshire) (DLY), Berkshire × (Duroc × Saba) (BDS), and Duroc × (Berkshire × Saba) (DBS) three-way crossbred pigs were compared. The results showed that DLY had the highest live weight, carcass weight, lean meat percentage, drip loss, glycolysis potential, muscle diameter, and relative mRNA expression levels of type IIb muscle fibers as well as the lowest ultimate pH (p < 0.05). The lightness value of DBS was the highest (p < 0.05). Among the three crossbred pigs, myristic, arachidic, palmitoleic, and eicosenoic acids were the highest in BDS. These results indicated that the carcass traits of local crossbred pigs were worse than those of DLY pigs, but meat quality was markedly higher, with BDS showing the best meat quality.

Mechanisms and treatments of neuropathic itch in a mouse model of lymphoma.

Our understanding of neuropathic itch is limited due to a lack of relevant animal models. Patients with cutaneous T cell lymphoma (CTCL) experience severe itching. Here, we characterize a mouse model of chronic itch with remarkable lymphoma growth, immune cell accumulation, and persistent pruritus. Intradermal CTCL inoculation produced time-dependent changes in nerve innervations in lymphoma-bearing skin. In the early phase (20 days), CTCL caused hyperinnervations in the epidermis. However, chronic itch was associated with loss of epidermal nerve fibers in the late phases (40 and 60 days). CTCL was also characterized by marked nerve innervations in mouse lymphoma. Blockade of C-fibers reduced pruritus at early and late phases, whereas blockade of A-fibers only suppressed late-phase itch. Intrathecal (i.t.) gabapentin injection reduced late-phase, but not early-phase, pruritus. IL-31 was upregulated in mouse lymphoma, whereas its receptor Il31ra was persistently upregulated in Trpv1-expressing sensory neurons in mice with CTCL. Intratumoral anti-IL-31 treatment effectively suppressed CTCL-induced scratching and alloknesis (mechanical itch). Finally, i.t. administration of a TLR4 antagonist attenuated pruritus in early and late phases and in both sexes. Collectively, we have established a mouse model of neuropathic and cancer itch with relevance to human disease. Our findings also suggest distinct mechanisms underlying acute, chronic, and neuropathic itch.

Screening of chemical pulp, revisiting technology options, and the state‐of‐the‐art equipment—A critical review

AbstractScreening of pulp can be expressed as a process where solid contaminants are removed from a pulp slurry without an excessive loss of fibres of acceptable quality. The impurities originate from the feedstock, or they are generated during the transport, handling, storage, or pulping process. The most typical impurities include bark, fibre bundles or shives, knots, plastic, rubber, and sand. Moreover, there are also other objectives for screening, such as the improvement of the pulp quality, savings in bleaching chemical consumption, and protection of process equipment. In industrial applications, pulp screening is typically carried out with more than one screen for a more beneficial screening result. The pulp screening equipment can be divided into different types by the separation technique employed, such as atmospheric or pressurized screens, centrifugal screens, vibrating screens, etc. In addition, there are other types of related equipment that are common in the pulp screening process, such as knotters, refiners, and hydrocyclones. The main objective of this review is to discuss the advantages and disadvantages of modern screening equipment as well as introduce contemporary screening strategies for chemical pulp mills.

Design and fabrication of a chalcogenide hollow-core anti-resonant fiber for mid-infrared applications.

Chalcogenide hollow-core anti-resonant fibers (HC-ARFs) are a promising propagation medium for high-power mid-infrared (3-5 µm) laser delivery, while their properties have not been well understood and their fabrications remain challenging. In this paper, we design a seven-hole chalcogenide HC-ARF with touching cladding capillaries, which was then fabricated from purified As40S60 glass by combining the "stack-and-draw" method with a dual gas path pressure control technique. In particular, we predict theoretically and confirm experimentally that such medium exhibits higher-order mode suppression properties and several low-loss transmission bands in the mid-infrared spectrum, with the measured fiber loss being as low as 1.29 dB/m at 4.79 µm. Our results pave the way for the fabrication and implication of various chalcogenide HC-ARFs in mid-infrared laser delivery systems.

Temperature and rate-dependent plastic deformation mechanism of carbon nanotube fiber: Experiments and modeling

High-performance carbon nanotube (CNT) fibers inevitably encounter complicated thermal environments while used in aerospace structures and intelligent actuators. Catastrophic damage is unavoidably induced due to the loss of their mechanical properties. Herein, a modified Hopkinson bar and an in-situ SEM tensile equipment were introduced to study the high-temperature time-dependent mechanical behaviors and microstructure evolution of individual CNT fibers. It was found that the interaction between CNTs was weakened by thermal expansion and defects were introduced into CNTs by thermal oxidation. In addition, the effects of temperature on the viscoplastic strain transition and durability of CNT fibers were studied through a series of relaxation experiments. A shear-lag unit cell and a three-level mathematical model were developed for describing the hierarchical structure evolution of CNT fibers. These models clarified the mechanism of strength loss of CNT fibers at high temperatures and characterized the effect of thermal expansion on their microstructure and mechanical properties. The overlap length and the distance between tubes as a function of temperature were discussed. According to the modeling, an effective strategy was proposed to improve the mechanical properties of CNT fibers at high temperatures by restraining thermal expansion and thermal oxidation. This work would provide crucial theoretical and experimental guidance for the improvement of the thermal dynamic stability of CNT fibers and their composites in extremely high-temperature operating conditions.

High-resolution spatiotemporal changes in dominant frequency and structural organization during persistent atrial fibrillation.

Analyze changes in frequency activity and structural organization that occur over time with persistent atrial fibrillation (AF). Little is known about the frequency characteristics of the epicardium during transition from paroxysmal to persistent AF. Accurate identification of areas of high dominant frequency (DF) is often hampered by limited spatial resolution. Improvements in electrode arrays provide high spatiotemporal resolution, allowing for characterization of the changes that occur during this transition. AF was induced in adult Yorkshire swine by atrial tachypacing. DF mapping was performed using personalized mapping arrays. Histological analysis and late gadolinium enhanced magnetic resonance imaging were performed to determine structural differences in fibrosis. The left atrial epicardium was associated with a significant increase in DF in persistent AF (6.5 ± 0.2 vs. 7.4 ± 0.5 Hz, P = 0.03). The organization index (OI) significantly decreased during persistent AF in both the left atria (0.3 ± 0.03 vs. 0.2 ± 0.03, P = 0.01) and right atria (0.33 ± 0.04 vs. 0.23 ± 0.02, P = 0.02). MRI analysis demonstrated increased ECV values in persistent AF (0.19 vs 0.34, paroxysmal vs persistent, P = 0.05). Tissue sections from the atria showed increase in fibrosis in pigs with persistent AF compared to paroxysmal AF. Staining demonstrated decreased myocardial fiber alignment and loss of anisotropy in persistent AF tissue. Changes in tissue organization and fibrosis are observed in the porcine model of persistent AF. Alterations in frequency activity and organization index can be captured with high resolution using flexible electrode arrays.

Effect of steel fibre and manufactured sand on mechanical properties of alkali-activated slag green cementitious material after high temperature

This study investigated the mechanical properties of alkali-activated slag cementitious material (AASCM) after exposure to 20–800 ℃ considering the effect of steel fibre content and aggregate type to promote the use of AASCM in structural engineering. The volume contents of steel fibre were 0%, 0.5%, 1.0% and 1.5%, and the aggregate types were manufactured sand and natural river sand. The residual compressive, tensile strength and mass loss were determined. Besides, the microstructure and phase composition of AASCM before and after high temperature exposure were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the tensile and compressive properties of manufactured sand AASCM were inferior to that of natural river sand after high temperature exposure. Below 600 ℃, steel fibre can improve the mechanical properties of AASCM. Steel fibre oxidation fails and effectively loses its strengthening effect on AASCM with the temperature reaching 800 ℃, resulting in a notable decrease in strength of AASCM. The models for calculating mass loss, compressive strength, and tensile strength of steel fibre reinforced AASCM after high temperature exposure were established.

Conditionally dominant negative impacts of clinically recessive TNNT1 myopathy mutations.

TNNT1 nonsense mutation causing premature termination of the translation of slow skeletal muscle troponin T (ssTnT) has been reported with recessive inheritance and loss-of-function phenotypes. We studied the phenotypes of mouse models of Tnnt1 myopathies for pathological impacts besides the loss of slow fiber functions. Mice with a knock-in stop codon at Glu180 mimicking the Amish nemaline myopathy (ANM-KI) show similar recessive phenotypes to that of Tnnt1-knockout (ssTnT-KO) mice (Wei et al. J. Physiol. 2014) with loss of slow fibers, low fatigue-resistance, active regeneration, inflammatory immune cell infiltration and compensatory hypertrophy of fast fibers in slow fiber-rich muscles. ANM-KI mice showed significantly more loss of slow fibers, more active regeneration, worse post-fatigue recovery and more hypertrophy of fast fibers than that of ssTnT-KO mice at young age and advancing with age. A feature of TNNT1 premature termination mutations is decreased tropomyosin-binding affinity and loss of thin filament incorporation. Therefore, the more severe than ssTnT-KO myopathic phenotypes of ANM-KI mice suggest negative impacts of non-myofilament incorporated TnT fragment on causing degeneration of slow and mix fiber type muscles. Since hypertrophy of fast fibers was not seen in ANM-KI mice before 7 days of age when soleus muscle is not utilized due to premature neuromuscular development, work- and/or load-induced slow and mix fiber muscle injury may worsen the negative impacts by increasing the total level of non-myofilament incorporated TnT and fragments from the release of fast skeletal muscle TnT in mix type fibers. Since non-myofilament-incorporated TnT is rapidly degraded in normal muscle cells, the cytotoxic effect of non-myofilament-incorporated TnT and fragment may have high potency (Jeong et al. AJP, 2009) and this pathogenic mechanism presents a molecular target for the treatment of TNNT1 myopathies and for improving muscle health of carriers.

Anti-icing Performance Evaluation of OPGW Based on BOTDA and OTDR

Under certain icing load, the optical fiber of OPGW is seriously affected by stress, which will not only affect the operation quality of line communication, but also threaten its own and line safety, such as cable breaking, tower falling and other accidents. At present, OTDR is mainly used to test the optical path loss of the optical fiber in the OPGW after icing, but that can’t reflect and judge the damage state of the OPGW accurately. In this paper, a method combining BOTDA and OTDR is proposed to detect the damaged state of OPGW after icing. Based on this, the anti icing performance is divided into healthy state, sub-health state and fault state.

Smart nanostructures for targeted oxygen-producing photodynamic therapy of skin photoaging and potential mechanism.

Background: Photodynamic therapy increases collagen and decreases solar fibrosis in photoaged skin; however, the efficacy of photodynamic therapy is limited in tissues with a hypoxic microenvironment. Methods: A novel autogenous oxygen-targeted nanoparticle, named MCZT, was synthesized based on the zeolitic imidazole framework material ZIF-8, methyl aminolevulinate, catalase and an anti-TRPV1 monoclonal antibody, and its effects on skin photoaging were investigated. Results: MCZT was successfully synthesized and showed uniform particle size, good dispersion, and excellent biocompatibility and safety. Moreover, MCZT effectively alleviated UV-induced inflammation, cellular senescence and apoptosis in HFF-1 cells. In in vivo models, MCZT ameliorated UV-evoked erythema and wrinkling, inflammation and oxidative stress, as well as the loss of collagen fibers and water, in the skin of mice. Conclusion: These findings suggest that MCZT holds promising potential for the treatment of skin photoaging.

Small-fibre neuropathy in leprosy the role of in vivo confocal microscopy: A cross-sectional study.

Background Leprosy (or Hansen's disease) continues to present considerable challenges regarding containment and early diagnosis. Leprosy is considered to be primarily a neural disease that first affects the sensory function of small fibres. Although the condition is well described in terms of clinical manifestations and histology, few studies have been undertaken to detect damage done to small-fibre sensory nerves. In vivo confocal microscopy is a useful tool for conducting a detailed evaluation of these structures, although its use in individuals affected by leprosy has still not been explored. Objective To evaluate in vivo confocal microscopy findings in Hansen's disease patients and their association with clinical variables relating to this disease. Method A cross-sectional case-series type study was carried out between October 2019 and May 2021, in Recife, Pernambuco, Brazil. Socio-demographic and clinical data were gathered from 21 patients with leprosy. The douleur neuropathique 4 neuropathic pain questionnaire was used to evaluate pain. In vivo confocal microscopy of the cornea was employed to evaluate the small-calibre fibres. Findings were compared with those for a control group of 23 healthy individuals. Results In relation to clinical parameters, 90.5% of the patients were classified as "multibacillary" according to the World Health Organization criteria, and 70% as dimorphic or borderline, in accordance with the Madrid classification. Around 52.4% had received a diagnosis after one year or less of living with the disease, while 95.2% presented alterations in small-fibre sensory function and 35% presented such alterations in the large fibre. Neuropathic pain was present in 81% of the patients. In vivo confocal microscopy found no statistically significant difference in mean age and distribution according to sex between the Hansen disease patients and the control group of healthy individuals. The median-of-means for dendritic cells and volume of sub-basal nerve fibres in the control group were used to test for normality. Both eyes of all leprosy patients examined contained higher number of dendritic cells than the median value and a volume of sub-basal nerve fibres lower than the mean. These differences were statistically significant (P < 0.001 and P < 0.001, respectively). Multibacillary individuals had a median number of dendritic cells two times that of paucibacillary individuals (P = 0.035). Limitations No association was found between the variables examined using in vivo confocal microscopy and clinical variables relating to small-fibre damage, the neuropathic pain questionnaire or alterations detected by the neurological examination. We believe, however, that Cochet-Bonnet esthesiometry of the cornea may have revealed such an association. Conclusion In vivo confocal microscopy is a useful diagnostic tool for detecting small fibre loss in individuals affected by leprosy and may constitute a useful addition to the range of tools available to help curb the effects of neuropathy in these patients.

Extremely Efficient DFB Lasers with Flat-Top Intra-Cavity Power Distribution in Highly Erbium-Doped Fibers.

High-performance erbium-doped DFB fiber lasers are presently required for several sensing applications, whilst the current efficiency record is only a few percent. Additionally, a flat-top intra-cavity power distribution that is not provided in traditional DFB lasers is preferred. Moreover, cavity lengths of <20 cm are attractive for fabrication and packaging. These goals can be achieved using highly erbium-doped fiber (i.e., 110 dB/m absorption at 1530 nm), providing high gain with proper engineering of coupling coefficients. In this paper, for a given background fiber loss, first the optimum intra-cavity signal powers for various pump powers are numerically calculated. Then, for a fully unidirectional laser, optimum coupling profiles are determined. Design diagrams, including contour maps for optimum cavity lengths, maximum output powers, maximum intra-cavity signal powers, and quality factors considering various pump powers and background fiber losses, are presented. The laser pump and intra-cavity signal distribution are also calculated for a realistic, feasible modified coupling profile considering a strong unidirectionality. The DFB laser is finally simulated using generalized coupled-mode equations for such modified profiles. The efficiency of more than 22% can be realized, which is the highest reported for DFB lasers based only on erbium-doped fiber.

Loss in hollow-core optical fibers: mechanisms, scaling rules, and limits

Over the past few years, progress in hollow-core optical fiber technology has reduced the attenuation of these fibers to levels comparable to those of all-solid silica-core single-mode fibers. The sustained pace of progress in the field has sparked renewed interest in the technology and created the expectation that it will one day enable realization of the most transparent light-propagating waveguides ever produced, across all spectral regions of interest. In this work we review and analyze the various physical mechanisms that drive attenuation in hollow-core optical fibers. We consider both the somewhat legacy hollow-core photonic bandgap technology as well as the more recent antiresonant hollow-core fibers. As both fiber types exploit different guidance mechanisms from that of conventional solid-core fibers to confine light to the central core, their attenuation is also dominated by a different set of physical processes, which we analyze here in detail. First, we discuss intrinsic loss mechanisms in perfect and idealized fibers. These include leakage loss, absorption, and scattering within the gas filling the core or from the glass microstructure surrounding it, and roughness scattering from the air–glass interfaces within the fibers. The latter contribution is analyzed rigorously, clarifying inaccuracies in the literature that often led to the use of inadequate scaling rules. We then explore the extrinsic contributions to loss and discuss the effect of random microbends as well as that of other perturbations and non-uniformities that may result from imperfections in the fabrication process. These effects impact the loss of the fiber predominantly by scattering light from the fundamental mode into lossier higher-order modes and cladding modes. Although these contributions have often been neglected, their role becomes increasingly important in the context of producing, one day, hollow-core fibers with sub-0.1-dB/km loss and a pure single-mode guidance. Finally, we present general scaling rules for all the loss mechanisms mentioned previously and combine them to examine the performance of recently reported fibers. We lay some general guidelines for the design of low-loss hollow-core fibers operating at different spectral regions and conclude the paper with a brief outlook on the future of this potentially transformative technology.