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We propose to inscribe a compact and reproducible long-period fiber grating (LPFG) in a standard single-mode fiber by a CO2-laser splicer that allows twisting the fiber stepwise during the laser heating process. The operation induced an azimuthal refractive index modulation, enabling the inscribed grating with asymmetric cladding modes coupling. By optimizing the parameters, the grating contrast with more than 30 dB was achieved with a 5.9 mm length. The approach could also fabricate ultra-LPFG, and the gratings with different diffraction orders are inscribed experimentally. The maximum twisting and strain sensitivities of the grating with ${LP}_{1,3}$ modes were achieved to be −0.09 nm/(rad/m) and −0.79 pm/ $\mu \varepsilon $ , respectively. The proposed method has not only overcome the limitation of laser spot size on grating fabrication by CO2-laser splicer but also has the advantage of flexible fabrication of the different grating structures for practical applications.

We demonstrate the fabrication of a broadband helical long-period grating (HLPG) in a double-cladding fiber. The proposed method uses a double-side CO2-laser automated inscription technique that allows for the rotation and moving of the fiber during laser irradiation. Gratings with different pitches have been fabricated, covering a broadband wavelength range. A 10-dB bandwidth of 160 nm was achieved for the grating with a resonance wavelength of 1554.2 nm, which featured a compact length of 5.98 mm. Additionally, by splicing the HLPG with two-mode fiber (TMF), the HLPG-TMF structure could convert the fundamental mode to the first-order orbital angular momentum (OAM) core mode with a bandwidth of more than 130 nm. The proposed HLPG could be adopted as a broadband tunable mode converter, OAM generator, and broadband fiber filter, which can be used in fiber communication and sensing systems.

We proposed a high-sensitivity torsion sensor based on the helical long-period grating (HLPG) inscribed in the cladding-etched double cladding fiber (DCF). The torsion sensitivity has been greatly improved by reducing the cladding diameter of the DCF, from 0.342 to 1.162 nm/(rad/m), which is one order of magnitude higher than that of the conventional long-period fiber grating (LPFG). The cladding mode coupling characteristics during the etching process are also investigated experimentally. The DCF-HLPG has a low strain and temperature sensitivity, and the maximum strain sensitivity is only about 0.0022 nm/ $\mu \varepsilon $ . The proposed DCF-HLPG has a potential application as a high-sensitivity torsion sensor with low strain and temperature crosstalk.

We investigated theoretically and experimentally the long-period fiber gratings (LPFGs) inscribed in the tapered few-mode fiber (FMF), and successfully generated the LP11 core mode in a broad wavelength range. Simulation and experimental studies have demonstrated that the phase matching curve of the FMF-LPFG can be changed through fiber tapering, thereby moving the dispersion turning point (DTP) to the communication band. The tunable ultra-broadband mode converter can be realized based on the DTP-LPFG. We investigated the relationship between the DTP of the FMF-LPFGs and fiber diameter. The LPFGs were fabricated in the FMF with diameters of $100~\mu \text{m}$ and $90~\mu \text{m}$ , with 10-dB bandwidth of 504 nm and 450 nm, respectively. The 10-dB bandwidth of the mode converter and the corresponding wavelength range can be adjusted by changing the fiber diameter.

We demonstrated the fabrication of helical long-period gratings (HLPGs) in a seven-core fiber (SCF) using CO2-laser irradiation. The mode coupling from the fundamental core mode to both LP11 core mode and LP17 cladding mode can be realized using the HLPGs with different grating periods. The torsion, refractive index, temperature, axial strain, and polarization-dependent loss characteristics of the HLPGs in different cores were investigated experimentally. The HLPG was found to have a high torsion sensitivity of 0.61 nm/(rad/m), refractive index sensitivity of −4837.8 nm/RIU when the surroundings refractive index changes in the range of 1.445–1.454, temperature sensitivity of 0.17 nm/°C and strain sensitivity of −9.6 pm/μϵ. The proposed SCF-HLPGs could have applications as multi-channel high-sensitivity fiber sensors, and multicore few-mode mode converters for space division multiplexing.

We demonstrated the fabrication of orbital angular momentum (OAM) mode convertors (MCs) operating at 1.3–2.1-μm waveband based on the helical long-period gratings (HLPGs) inscribed in the few-mode fiber (FMF) using a CO2 laser. The ±1st, ±2nd, and ±3rd OAM mode can be directly generated by the HLPGs with efficiencies of more than 90%. The torsion sensitivities of the first-, second-, and third-order OAM modes in 2-μm waveband are 0.52, 0.55, and 0.36 nm/(rad/m), which has increased by 5.8 times, 2.8 times, and 1.6 times compared to that in 1.3-μm waveband, respectively. The strain sensitivities of the first-, second-, and third- order OAM modes in 2-μm waveband are −4.2, −4.0, and −4.9 pm/ $\mu \varepsilon $ , which has increased by 2.3 times, 2 times, and 2.2 times compared to that in 1.3-μm waveband, respectively. The proposed OAM mode MCs based on the HLPGs can function as not only promotion of optical communication system but also high-torsion sensitivity sensors in the sensing field.

We propose a novel fiber device based on arc-induced long-period fiber gratings (LPFGs) in a hollow core silica capillary. This device is made up of a lead-in single-mode fiber (SMF), LPFGs in capillary (CLPFGs), and a lead-out SMF, with a tapered air cavity (TAC) connecting SMF and capillary. The transmissive characteristics of capillary with and without LPFGs are analyzed theoretically and experimentally. Mode coupling of CLPFGs at longer wavelength could be enhanced, as well as the sensing performance increases times over the capillary without gratings. The refractive index (RI) sensitivity can reach to be 15 713.5 nm/RIU in the RI range from 1.451 to 1.456. Moreover, with the asymmetric index distribution induced in the capillary, the CLPFGs present vector bending properties that the bending sensitivities are 79.4 and −8.8 nm/ $\text{m}^{-{1}}$ , for bending directions at 0° and 180°, respectively. Furthermore, the proposed device shows negligible change to the external temperature variation, which could solve the cross-sensitivity problem. With the advantages of compactness, low cost, and ease of fabrication, the proposed device is potential in high-sensitivity RI sensing fields and vector bending measurement.

We demonstrate the multiparametric monitoring of directional bending, torsion, and temperature based on helical long-period gratings (HLPGs) in a triangular four-core fiber (FCF) using CO2 laser irradiation. The simulations investigated the stress-relaxing effect of the stress-applying parts due to CO2 laser heating. In the experiments, the HLPGs with a period of 435 μm and a period number of 60 induced in FCF have been investigated for multiparametric monitoring. The directional bending sensing characteristics of FCF-HLPGs exhibit that at the curvature ranges A and B, the maximum bending sensitivities are −47.24 and 48.47 dB/m−1 obtained at −60°, respectively. And their sensitivities show the sine function behavior with curvature directions from −180° to 180°. The torsion sensitivity based on coupling efficiency variation is −0.16%/(rad/m) in the range from −10 to 10 rad/m. The temperature sensitivity based on wavelength variation is 0.123 nm/°C, and the intensity response on temperature can be negligible. The proposed FCF-HLPGs is potential in practical application for multiparametric monitoring.

We propose and demonstrate the inscription of multi-cascaded long-period fiber gratings (LPFGs) in a few-mode fiber using a CO2-laser. The multi-cascaded LPFGs containing three gratings were fabricated successfully. The first LPFG was used to realize the mode conversion from LP01 mode to LP11 mode, the second one was used to convert LP11 mode to LP21 mode, and the third one achieved the higher-order mode conversion from LP21 mode to LP31 mode. The second-order and third-order orbital angular momentum (OAM) modes can be generated using the cascaded LPFGs with the second and third gratings, respectively. The multi-cascaded LPFGs have the promising potential to be adopted as mode converters and mode scramblers in the mode division multiplexing system thanks to the flexible mode conversion among different higher-order modes.

The influences on the tuning range of a wavelength-tunable L-band mode-locked fiber lasers incorporating a long-period fiber grating (LPFG) are investigated. Through controlling both resonance wavelength and bandwidth of the LPFG, the net gain of the laser can be designed appropriately, hence leading to an optimized tuning range of the L-band mode-locked lasers. A wide spectral tuning range of 23.98 nm is obtained when using the LPFG with 21.60 nm bandwidth. Benefiting from the narrow band optical attenuation characteristic of LPFG, the lowest power variation of the laser is merely 4.15 µW/nm. Moreover, theoretical gain analysis corresponds to the experimental observation well.

Recent years have witnessed various breakthroughs in the research of graphene-related materials since the emergence of a few promising techniques for large-scale production of mono- or multi-layer graphene films. With the help of various surface modification methods, the physicochemical properties of graphene are greatly improved and graphene shows superior sensitivity and selectivity for biological molecular analysis. This paper selectively reviews the application of graphene-based biosensors, especially for detecting nucleic acid, protein and biological small molecules. In addition, future perspectives of graphene-based biosensors are also prospected.

Hu sheep is one of the most distinctive local sheep breeds in China, while investigations concerning its cell biology and molecular genetics are still scarce. To preserve the valuable genetic resources of the Hu sheep, we established a Hu sheep fibroblast line from 35 sheeps' ear marginal tissues using explant culture and cryopreservation techniques, and its biological characteristics were identified, including cell morphology, growth curve, karyotype, isoenzyme polymorphism, and expression of exogenous fluorescent genes. The results showed that the viability of the fibroblasts before freezing was 96.54 ± 3.22% and 92.36 ± 2.77% after thawing, and there was no microbial contamination and cross-contamination; the growth curve of Hu sheep ear marginal fibroblasts displayed an obvious “S” shape; all somatic chromosomes were acrocentric autosomes, and only the two sex chromosomes (XY) were submetacentric; the normal number of chromosomes (2n= 54) was observed in 96.56 ± 2.89% of the cells; and the transfer efficiencies of four fluorescent proteins could achieve 37.4% with an optimized ratio of plasmid and lipofectamine. It could be concluded that this study has not only provided the biological characteristics of Hu sheep at cellular level, but also makes a valuable contribution to the preservation of the genetic resources of the Hu sheep.

The multi-vertebrae phenotype of the Mongolian sheep is not explained by Mendel's law. To test the hypothesis that the multi-vertebrae phenotype is related to HOXC-8 mutation or genomic imprinting, the sequences of exon-1 and exon-2 of the HOXC-8 gene of normal and multi-vertebrae Mongolian sheep were analysed. Bisulphite sequencing Polymerase Chain Reaction (PCR) was employed to compare the methylation status of cytosine-guanine (CpG) sites in HOXC-8 exon-1 region from normal and multi-vertebrae Mongolian sheep. No mutations were observed in HOXC-8 exon-1 or exon-2 of normal and multi-vertebrae Mongolian sheep. However, the level of DNA methylation in exon-1 of the HOXC-8 gene was much lower in the 13-vertebrae sheep than in the 14-vertebrae sheep. In the CpG island (293 bp), there were six, three and six methylated CpGs in the normal sheep samples and 23, 20 and 21 in the multi-vertebrae sheep samples, respectively. The ratio of methylated to non-methylated CpG dinucleotides in normal and multi-vertebrae sheep were 18.50±0.064 and 79.03±0.056% (P<0.01, by a t-test), respectively.

Background: Malignant peripheral nerve sheath tumors (MPNST) are rare neoplasms, usually arising from peripheral nerves or showing a nerve sheath differentiation. Primary MPNSTs of the scalp is exceptionally rare, and only sporadic cases have been reported recently.

Highly uniform and monodisperse core-shell microspheres composed of a polystyrene (PS) core and a copper shell were prepared by dispersion polymerization of styrene followed by electroless copper plating. The formation of copper shell on PS surface was confirmed by FESEM, TEM, XRD and TGA. As a result, the plating bath composition had an important influence on the morphology of PS/Cu composites. The addition of Na2EDTA and La2O3as a complexant and a stabilizer led to the formation of a more compact copper shell on PS surface. The formation mechanism was explored by the linear sweep voltammetry method, and the different morphology might mostly result from the various nucleation rates. Tailoring of shell thickness can be achieved through altering the loading of PS in the ECP bath. Conductivity of the PS/Cu composites with a shell thickness of 195 nm is up to 2.2×105S/m. The PS/Cu composites may have great potential to be used as fillers of anisotropic conductive film for their uniform diameter, low density and good conductivity.