Flexible and robust low-loss selenium-based multimaterial infrared fibers towards CO2 laser ablation.

A small-scale delivery medium for CO2 laser energy with stable performance, flexibility, and high-strength is crucial in extreme laser processing environments, especially for minimally invasive surgery in high-humidity, twisty and narrow channels. Here, flexible and robust multimaterial infrared fibers made of selenium-based chalcogenide glasses and thermoplastic polymer were developed with a low loss of 7.18 dB/m at 10.6 µm. The resulting fibers were capable of stably delivering single-mode CO2 laser with 0.42 W average power. Moreover, to achieve precise control over the fibers in the practical clinical environment, customized co-polymers of polyphenylene sulfone resin and polyvinylidene fluoride were used as the fiber built-in jackets. Consequently, the fibers exhibited hydrophobicity, thermostability, high tensile strength, and low bending stiffness. The results demonstrated that the fibers can be used to deliver CO2 laser energy for fabric cutting and bio-tissues ablation, making them attractive for CO2 laser material processing and minimally invasive laser surgery.

Discovering extremely low confinement-loss anti-resonant fibers via swarm intelligence.

In this work, we obtain extremely low confinement-loss (CL) anti-resonant fibers (ARFs) via swarm intelligence, specifically the particle swarm optimization (PSO) algorithm. We construct a complex search space of ARFs with two layers of cladding and nested tubes. There are three and four structures of cladding tubes in the first and second layer, respectively. The ARFs are optimized by using the PSO algorithm in terms of both the structures and the parameters. The optimal structure is obtained from a total of 415900 ARFs structures, with the lowest CL being 2.839×10-7 dB/m at a wavelength of 1.55 µm. We observe that the number of ARF structures with CL less than 1×10-6 dB/m in our search space is 370. These structures mainly comprise four designs of ARFs. The results show that the optimal ARF structures realized by the PSO algorithm are different from the ARFs reported in the previous literature. This means that the swarm intelligence accelerates the design and invention of ARFs and also provides new insights regarding the ARF structures. This work provides a fast and effective approach to design ARFs with special requirements. In addition to providing high-performance ARF structures, this work transforms the ARF designs from experience-driven to data-driven.

Hierarchical-morphology metafabric for scalable passive daytime radiative cooling.

Incorporating passive radiative cooling structures into personal thermal management technologies could effectively defend humans against intensifying global climate change. We show that large-scale woven metafabrics can provide high emissivity (94.5%) in the atmospheric window and high reflectivity (92.4%) in the solar spectrum because of the hierarchical-morphology design of the randomly dispersed scatterers throughout the metafabric. Through scalable industrial textile manufacturing routes, our metafabrics exhibit desirable mechanical strength, waterproofness, and breathability for commercial clothing while maintaining efficient radiative cooling ability. Practical application tests demonstrated that a human body covered by our metafabric could be cooled ~4.8°C lower than one covered by commercial cotton fabric. The cost-effectiveness and high performance of our metafabrics present substantial advantages for intelligent garments, smart textiles, and passive radiative cooling applications.

Use of machine learning to efficiently predict the confinement loss in anti-resonant hollow-core fiber.

The fundamental mode confinement loss (CL) of anti-resonant hollow-core fiber (ARF) is efficiently predicted by a classification task of machine learning. The structure-parameter vector is utilized to define the sample space of ARFs. The CL of labeled samples at 1550 nm is numerically calculated via the finite element method (FEM). The magnitude of CL is obtained by a classification task via a decision tree and k-nearest neighbors algorithms with the training and test sets generated by 290700 and 32300 labeled samples. The test accuracy, confusion matrices, and the receiver operating characteristic curves have shown that our proposed method is effective for predicting the magnitude of CL with a short computation runtime compared to FEM simulation. The feasibility of predicting other performance parameters by the extension of our method, as well as its ability to generalize outside the tested sample space, is also discussed. It is likely that the proposed sample definition and the use of a classification approach can be adopted for design application beyond efficient prediction of ARF CL and inspire artificial intelligence and data-driven-based research of photonic structures.

Gain-tailored Yb/Ce codoped aluminosilicate fiber for laser stability improvement at high output power.

A gain-tailored Ge-free Yb/Ce codoped aluminosilicate fiber is fabricated by MCVD combined with solution doping technique. Through regulating the temperature in the tube and designing the solution doping process, the refractive index profile of this fiber is close to a step-index without any center dip. The laser performance of this fiber is proved through contrast experiments with conventional fiber in a kW-level MOPA setup. The gain-tailored fiber amplifier presents a beam quality of M2 ~1.43 at 1.2 kW. Its MI threshold is 1.25 kW, about 1.74 times as much as that of the conventional fiber amplifier. The laser slope efficiency of the gain-tailored fiber amplifier is 86.75%. Stabilized at an output power of 1.1 kW for 15 hours, the MI threshold does not decrease after this long-term operation, demonstrating a strong resistance to photodarkening effect. These results have confirmed that MCVD-fabricated gain-tailored Yb/Ce codoped aluminosilicate fibers have great potential in power scaling and output stability of high-power fiber lasers and amplifiers.

Design and fabrication of a heterostructured cladding solid-core photonic bandgap fiber for construction of Mach-Zehnder interferometer and high sensitive curvature sensor.

A heterostructured cladding solid-core photonic bandgap fiber (HCSC-PBGF) is designed and fabricated which supports strong core mode and cladding mode transmission in a wide bandgap. An in-line Mach-Zehnder interferometer (MZI) curvature sensor is constructed by splicing single mode fibers at both ends of a HCSC-PBGF. Theoretical analysis of this heterostructured cladding design has been implemented, and the simulation results are consistent with experiment results. Benefiting from the heterostructured cladding design, an enhanced curvature sensing sensitivity of 24.3 nm/m-1 in the range of 0-1.75 m-1 and a high quality interference spectrum with 20 dB fringe visibility are achieved. In order to eliminate the interference of longitudinal strain and transverse torsion on the result of the curvature sensing experiment, we measure the longitudinal strain and transverse torsion sensing properties of HCSC-PBGF, and the results show that the impact is negligible. It is obvious that this high-sensitivity and cost-effective all fiber sensor with a compact structure will have a promising application in fiber sensing.

All fiber M-Z interferometer for high temperature sensing based on a hetero-structured cladding solid-core photonic bandgap fiber.

We proposed and experimentally demonstrated a high temperature fiber sensor using a hetero-structured cladding solid-core photonic bandgap fiber (HCSC-PBGF) for the first time to our knowledge. A hetero-structured cladding solid-core photonic bandgap fiber is designed and fabricated that supports vibrant core mode and cladding mode transmission. Then, an all fiber M-Z interference sensor is constructed by splicing single mode fiber at both ends of HCSC-PBGF without any other micromachining. The transmission characteristics of HCSC-PBGF are analyzed with a full-vector beam propagation method and a full-vector finite element method, and the simulation results are consistent with experiment results. The sensitivity of this fiber sensor is as high as 0.09 nm/°C when operating from room temperature to 1000 °C, and the fringe contrast keeps stable and clear. It is obvious that this all fiber sensor will have great application prospects in fiber sensing with the advantages of a compact structure, high sensitivity, and cost-effectiveness.

Active radiation hardening of Tm-doped silica fiber based on pump bleaching.

Tm-doped fiber laser or amplifier can be applied in varied adverse environments. In this work, we demonstrate the pump bleaching of Tm-doped silica fiber with 793nm pump source under gamma-ray irradiation in the range 50Gy-675Gy. The recovery time, the fiber slope efficiency and the fiber cladding absorption spectra after irradiation and bleaching have been measured. It is found that the recovery time and radiation induce absorption are positively associated with doses, however, the fiber slope efficiency of irradiated TDF and bleached TDF are both negatively correlated with doses. Based on the simulation of the fiber core temperature, the probable mechanism of pump bleaching is also discussed.