Search Results (11)

Anti-resonant hollow-core fibers (AR-HCFs) are emerging as highly promising candidates for high-power laser transmission and low-loss optical communication. Despite their advantages, issues such as scattering loss and core-mode instability remain significant obstacles for their practical implementation. In this study, we propose a novel hybrid fiber structure, the nano-core plus node-free anti-resonant hollow-core fiber (NPNANF), which integrates a solid, high-index nano-core within a six-tube node-free anti-resonant cladding. This hybrid design effectively enhances optical confinement while minimizing scattering losses, without relying solely on anti-resonant guidance. Numerical simulations employing the beam propagation method (BPM) and finite element analysis (FEA) demonstrate that an optimal nano-core diameter of 600 nm leads to a remarkable reduction in transmission loss to 0.025 dB/km at 1550 nm, representing a 99.8% decrease compared to conventional NANF designs. A comprehensive loss model is developed, incorporating contributions from confinement, scattering, and absorption losses in both the hollow cladding and the solid core. Parametric studies further illustrate the tunability of the fiber’s design for various high-performance applications. The proposed NPNANF achieves an ultra-low transmission loss of 0.025 dB/km, representing a >99.8% reduction compared to conventional NANF, while confining more than 92% of optical power within the nano-core. Its resistance to bending loss, strong modal stability, and balance between hollow-core and solid-core guidance highlight the advantages of NPNANF for long-haul optical communication and high-power photonics. Full article

Low-loss, high-birefringence, bend-resistant hollow-core anti-resonant fibers for infrared wavelengths have important applications in the fields of precision interferometric sensing, laser systems, and optical communications. In this paper, an eight-tube cladding quasi-symmetric hollow-core anti-resonant fiber is proposed, and two other anti-resonant fibers are designed based on this fiber structure. The finite element analysis method is used to numerically analyze the limiting loss, birefringence coefficient, bending resistance, and other properties of the three optical fibers after the optimized design. The results show that the limiting loss of the three optical fibers at λ = 1.55 μm is lower than 10⁻⁴ magnitude, and all of them obtain a birefringence coefficient of 10⁻⁴ magnitude; at the same time, the three optical fibers have their own characteristics and advantages, and the first optical fiber can reach a birefringence coefficient of 9.25 × 10⁻⁴ at λ = 1.52 μm.The limiting loss at λ = 1.55 μm is 3.42 × 10⁻⁵ dB/km. The minimum bending radius of the three types of anti-resonant fibers is less than 40 mm, which represents good bending characteristics, and the eight-tube cladding quasi-symmetric optical fiber has a bending loss of less than 2.10 × 10⁻³ dB/km when the bending radius is 28 mm. The three types of optical fibers have obtained good results in improving the mutual constraints between low limiting loss and high birefringence, with better results than the other two types. The obtained results have high development potential. Full article

In this paper, we propose a novel type of hollow-core anti-resonance fiber (HC-ARF). The cladding region of this fiber is formed by a combination of nested tubes and U-shaped tubes, and the centrally symmetric arrangement significantly reduces sensitivity to polarization. The influence of parameters on the performance of the designed HC-ARF LMA is analyzed by a finite element algorithm. The simulation results demonstrate that the designed structure achieves a large mode area of 3180 µm², bending loss of 2 × 10⁻² dB/km, and confinement loss of 5 × 10⁻³ dB/km at a wavelength of 1064 nm. Similarly, at a wavelength of 1550 nm, the large mode area, bending loss, and confinement loss are 3180 µm², 1.4 × 10⁻² dB/km, and 4 × 10⁻² dB/km, respectively. These results indicate unprecedentedly large mode areas and ultra-low losses compared to previous studies. Within the bending radius under consideration, the bending loss remains below 1.35 × 10⁻² dB/km. Furthermore, by increasing the fiber radius, the large mode area can reach an extraordinary 6250 µm². The proposed device exhibits excellent mode area and outstanding polarization insensitivity, along with favorable bending performance. We believe that the designed fiber holds promising applications in high-power miniaturized fiber lasers, fiber amplifiers, and various high-power fiber communication systems, and it can be applied in sensors that require polarization insensitivity and better bending performance. Full article

A large core size and bending resistance are very important properties of mid-infrared energy transfer fibers, but large core sizes usually lead to the deterioration of bending properties. A negative-curvature nested node-free anti-resonant hollow-core fiber (AR-HCF) based on quartz is proposed. It was made by adding a nested layer to a previous AR-HCF design to provide an additional anti-resonance region while keeping the gap between adjacent tubes strictly correlated with the core diameter to produce a node-free structure. These features improve the fiber’s bending resistance while achieving a larger core diameter. The simulation results show that the radial air–glass anti-resonant layer is increased by the introduction of the nested anti-resonant tube, and the weak interference overlap between the fiber core and the cladding mode is reduced, so the fiber core’s limiting loss and sensitivity to bending are effectively reduced. When the capillary wall thickness t of the fiber is 0.71 μm, the core diameter D is 70 μm, the ratio of the inner diameter of the cladding capillary to the core diameter d/D is 0.62, the diameter of the nested tube is d₀ = 29 μm, the fiber has a lower limiting loss at the wavelength of 2.79 μm, and the limiting loss is 3.28 × 10⁻⁴ dB/m. At the same time, the optimized structure also has good bending resistance. When the bending radius is 30 mm, the bending loss is only 4.72 × 10⁻² dB/m. An anti-bending low-loss micro-structure hollow fiber with a bending radius of less than 30 mm was successfully achieved in the 2.79 μm band. An anti-bending low-loss anti-resonant hollow-core fiber with this structure constitutes a reliable choice for the light guiding system of a 2.79 μm band Er, Cr: YSGG laser therapy instrument. Full article

The laser tube bending process (LTBP) is a new and powerful manufacturing method for bending tubes more accurately and economically by eliminating the bending die. The irradiated laser beam creates a local plastic deformation area, and the bending of the tube occurs depending on the magnitude of the heat absorbed by the tube and its material characteristics. The main bending angle and lateral bending angle are the output variables of the LTBP. In this study, the output variables are predicted by support vector regression (SVR) modeling, which is an effective methodology in machine learning. The SVR input data is provided by performing 92 experimental tests determined by the design of the experimental techniques. The measurement results are divided into two sub-datasets: 70% for the training dataset, and 30% for the testing dataset. The inputs of the SVR model are process parameters, which can be listed as the laser power, laser beam diameter, scanning speed, irradiation length, irradiation scheme, and the number of irradiations. Two SVR models are developed for the prediction of the output variables separately. The SVR predictor achieved a mean absolute error of 0.021/0.003, a mean absolute percentage error of 1.485/1.849, a root mean square error of 0.039/0.005, and a determination factor of 93.5/90.8% for the main/lateral bending angle. Accordingly, the SVR models prove the possibility of applying SVR to the prediction of the main bending angle and lateral bending angle in LTBP with quite an acceptable accuracy. Full article

Coiled tubing (CT) is used as a velocity string to transport high-velocity gas in drainage gas recovery technology. Sand particles flowing at high speed can cause serious erosion of the pipe wall. Long-term erosion wear leads to the degradation of the string strength and can even cause local perforation. In order to study the erosion wear problem of CT, a gas–solid erosion experimental device was established for a full-size pipe with different radii of curvature. A 3D laser confocal technique was used to examine and characterize the microscopic erosion morphology of the inner wall of the CT. The CFD erosion model was selected based on the erosion test data of the inner wall of the CT, and the erosion results of the Finnie model show minimal error and good agreement compared with other models. The average value of the error of the maximum erosion rate at different radii of curvature is 8.3%. The effect of the radius of curvature, gas velocity and solid particle size on the maximum erosion rate of the inner wall of the CT was analyzed based on the Finnie model. The results reveal that erosion wear occurs on the inner wall of the CT’s outer bend. As the radius of curvature is reduced, the maximum erosion rate and area increase, and the position of the maximum erosion rate gradually shifts toward the inlet. The maximum erosion rate is positively correlated with the gas flow rate. However, as the particle size increases, the maximum erosion rate shows a trend of first increasing, then decreasing and finally stabilizing, with a critical particle size of 200 μm. This study can provide theoretical guidance and methods for improving the service life of CT. The erosion rate of the tubing in old wells can be reduced by controlling production and employing appropriate sand control methods, while the erosion rate of tubing in new wells can be reduced by adjusting the wellbore trajectory. Full article

Thickness thinning is one of the processing defects that tend to occur in traditional stamping or mechanical bending of the plate and tube. In the field of high mechanical performance requirements (such as pressure vessels), the thinning phenomenon cannot be ignored. Thermal stress forming has excellent characteristics of forming without thinning, but the forming angle of this method is small, thus limiting the promotion and application of the process in the field of the form. To solve the problem, thermal stress forming with the baffle pressure method (BPM) is proposed. The coupled thermodynamic model of BPM is established, and the bending angle and deformation mechanism of the BPM are investigated. Lastly, the grain size and microhardness are measured and discussed. Results of the bending angle show that the proposed method can increase the bending angle by 57.71 times compared with the traditional method. The bending angle of BPM is determined by both the thermal buckling and the baffle, and the baffle plays a major role. The results of grain size and microhardness analysis show that the method refines the grain size, increases the material microhardness by 1.31 times and thickens the deformation zone by about 2.75%. In addition, the analytical equation of beam bending with laser as the heat source is given in this paper; this has some significance for further enrichment and development of the basic theory of beam thermoplastic bending. Full article

The laser tube bending process (LTBP) process is a thermal non-contact process for bending tubes with less springback and less thinning of the tube. In this paper, the laser tube bending process will be studied experimentally. The length of irradiation and irradiation scheme are two main affecting process parameters in the LTBP process. For this purpose, different samples according to two main irradiation schemes (Circular irradiating scheme (CIS) and axial irradiating scheme (AIS)) and different lengths of laser beam irradiation (from 4.7 to 28.2 mm) are fabricated. The main bending angle of laser-bent tube, lateral bending angle, ovality, and thickness variations is measured experimentally, and the effects of the irradiating scheme and the length of irradiation are investigated. An 18 mm diameter, 1 mm thick mild steel tube was bent with 1100 Watts laser beam. The results show that for both irradiating schemes, by increasing the irradiating length of the main and lateral bending angle, the ovality and thickness variation ratio of the bent tube are increased. In addition, for a similar irradiating length, the main bending angle with AIS is considerably higher than CIS. The lateral bending angle by AIS is much less than the lateral bending angle with CIS. The results demonstrate that the ovality percentage and the thickness variation ratio for the laser-bent tube obtained by CIS are much more than the values associated with by AIS laser-bent tube. Full article

Laser forming is an emerging manufacturing process capable of producing either uncomplicated and complicated shapes by employing a concentrated heating source. The heat source movement creates local softening, and a plastic strain will be induced during the rise of temperature and the subsequent cooling. This contactless forming process may be used for the simple bending of sheets and tubes or fabrication of doubly-curved parts. Different studies have been carried out over recent years to understand the mechanism of forming and predicting the bending angle. The analysis of process parameters and search for optimized manufacturing conditions are among the most discussed topics. This review describes the main recent findings in the laser forming of single and multilayer sheets, composite and fiber-metal laminate plates, force assisted laser bending, tube bending by laser beam, the optimization technique implemented for process parameters selection and control, doubly-curved parts, and the analytical solutions in laser bending. The main focus is set to the researches published since 2015. Full article

TiO₂ nanotube arrays (TNAs) with tube lengths of 4, 6, and 7 μm were prepared via two-step anodization. Thereafter, ultraviolet (UV) photodetectors (PDs) with Au/TiO₂/Au structures were prepared using these TNAs with different tube lengths. The effects of TNA length and device area on the performance of the device were investigated using in situ Raman spectroscopy. The maximum laser/dark current ratio was achieved by using a TNA with a size of 1 × 1 cm² and a length of 7 μm, under a 532 nm laser. In addition, when the device was irradiated with a higher energy laser (325 nm), the UV Raman spectrum was found to be more sensitive than the visible Raman spectrum. At 325 nm, the laser/dark current ratio was nearly 24 times higher than that under a 532 nm laser. Six phonon modes of anatase TNAs were observed, at 144, 199, 395, 514, and 635 cm⁻¹, which were assigned to the E_g(1), E_g(2), B_1g(1), A_1g/B_1g(2), and E_g(3) modes, respectively. The strong low-frequency band at 144 cm⁻¹ was caused by the O-Ti-O bending vibration and is a characteristic band of anatase. The results show that the performance of TNA-based PDs is length-dependent. Surface-enhanced Raman scattering signals of 4-mercaptobenzoic acid (4-MBA) molecules were also observed on the TNA surface. This result indicates that the length-dependent performance may be derived from an increase in the specific surface area of the TNA. In addition, the strong absorption of UV light by the TNAs caused a blueshift of the E_g(1) mode. Full article

A method for fabricating robust and thin hollow-core optical fibers that carry mid-infrared light is proposed for use in endoscopic laser applications. The fiber is made of stainless steel tubing, eliminating the risk of scattering small glass fragments inside the body if the fiber breaks. To reduce the inner surface roughness of the tubing, a polymer base layer is formed prior to depositing silver and optical-polymer layers that confine light inside the hollow core. The surface roughness is greatly decreased by re-coating thin polymer base layers. Because of this smooth base layer surface, a uniform optical-polymer film can be formed around the core. As a result, clear interference peaks are observed in both the visible and mid-infrared regions. Transmission losses were also low for the carbon dioxide laser used for medical treatments as well as the visible laser diode used for an aiming beam. Measurements of bending losses for these lasers demonstrate the feasibility of the designed fiber for endoscopic applications. Full article