Multi-wavelength random fiber laser based on a tilted parallel inscribed apodized fiber Bragg grating array.

We propose and demonstrate a multi-wavelength random fiber laser (RFL) based on a novel, to the best of our knowledge, compact apodized fiber Bragg grating array (AFBGA). The AFBGA is fabricated by a femtosecond laser with the point-by-point tilted parallel inscription method. The characteristics of the AFBGA can be flexibly controlled in the inscription process. Hybrid erbium-Raman gain is used in the RFL and reduces the lasing threshold to sub-watt level. Stable emissions at two to six wavelengths are achieved with the corresponding AFBGAs, and more wavelengths are expected with higher pump power and AFBGAs containing more channels. A thermo-electric cooler is employed to improve the stability of the RFL, and the maximum wavelength and power fluctuations of a three-wavelength RFL are 64 pm and 0.35 dB, respectively. With flexible AFBGA fabrication and simple structure, the proposed RFL enriches the choice of multi-wavelength devices and has significant potential in practical applications.

Random fiber laser based on a partial-reflection random fiber grating for high temperature sensing.

A stable single wavelength random fiber laser (RFL) with a partial-reflection random fiber grating (PR-RFG) for high temperature sensing is proposed and demonstrated for the first time, to the best of our knowledge. The PR-RFG is fabricated with the help of a femtosecond laser, with its highest reflection peak significantly higher than all other reflection peaks, which can ensure the stability of this filter-free RFL. Theoretical calculations also show that such a PR-RFG should be designed with reflectivity in the range of ∼30%-90% to obtain one reflection peak significantly higher than other peaks. The threshold of this laser is only 6.4 mW. In addition, the RFL realizes temperature sensing in the range from 25°C to 500°C and has an optical signal-to-noise ratio of up to 70 dB.

Stable and low-threshold random fiber laser via Anderson localization.

We report a stable and low-threshold Er-doped random fiber laser (RFL) based on a femtosecond-laser-inscribed random-distributed-grating array (RDGA) as the random feedback. The RDGA had a reflectivity of 93.5%, and its properties were numerically analyzed based on the transfer matrix method. The threshold of the laser was significantly reduced to 5.7 mW, and the linewidth was ~0.4 pm near the threshold as the Anderson localization effect existing in the RDGA significantly improved the laser quality factor (4 × 106). In addition, we propose a method to select RFL lasing modes by stretching a fiber grating filter used in the cavity with different axial strains. The center wavelength hardly drifted and the maximum jitter value of the peak power was less than 0.12 dB over 1 hour for the selected three lasing modes, which indicated that our laser operation was quite stable.

catena-Poly[[[tetra-aqua-zinc(II)]-µ-4,4'-bipyridine-κN:N'] benzene-1,4-di-carboxyl-ate].

In the title compound, {[Zn(C(10)H(8)N(2))(H(2)O)(4)](C(8)H(4)O(4))}(n), the Zn(II) atoms, lying on a twofold rotation axis, are bridged by 4,4'-bipyridine ligands, resulting in a linear chain along the b axis. In the chain, the Zn(II) atom adopts a slightly distorted octa-hedral coordination geometry involving four water mol-ecules at the equatorial positions. The noncoordinated benzene-1,4-dicarboxyl-ate anion, which is also located on a twofold rotation axis, bridges adjacent chains through O-H⋯O hydrogen bonds, forming a three-dimensional supra-molecular network.

1,1'-Dimethyl-4,4'-(propane-1,3-di-yl)dipyridinium tetra-bromidocadmate(II).

In the cation of the title compound, (C(15)H(20)N(2))[CdBr(4)], the dihedral angle between the two pyridine rings is 70.85 (5)°. An inter-molecular π-π inter-action between the pyridine rings [centroid-centroid distance = 3.900 (4) Å] is observed. The Cd(II) atom has a distorted tetra-hedral coordination.

5-Amino-3-(4-pyrid-yl)isoxazole.

In the title compound, C(8)H(7)N(3)O, there are two independent mol-ecules in the asymmetric unit, in which the angles between the pyridine ring and the isoxazole ring are 35.8 (6) and 10.6 (2)°. The crystal packing is stabilized by N-H⋯N hydrogen bonds, which result in the mol-ecules forming a two-dimensional supra-molecular layer.

1,1'-Dimethyl-4,4'-bipyridinium bis-(tetra-fluorido-borate).

In the title compound, C(12)H(14)N(2) (2+)·2BF(4) (-), the cation has a centre of symmetry at the mid-point of the central C-C bond. π-π inter-actions, with a shortest atom-to-atom distance of 3.757 (4) Å, extend the crystal structure into a one-dimensional supra-molecular chain.

Synthesis and characterization of chitosan/ZnO nanoparticle composite membranes.

Novel chitosan/ZnO nanoparticle (CS/nano-ZnO) composite membranes were prepared via the method of sol-cast transformation and studied by UV-vis absorption spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray fluorescence spectrometry (EDX). The characterization revealed that ZnO nanoparticles dispersed homogeneously within the chitosan matrix. The mechanical and antibacterial properties of the product were investigated. The results showed that the ZnO content had an effect on the mechanical properties of CS/nano-ZnO composite membranes, and that the antibacterial activities of CS membranes for Bacillus subtilis, Escherichia coli, and Staphylococcus aureus were enhanced by the incorporation of ZnO. Further, CS/nano-ZnO composite membranes with 6-10 wt% ZnO exhibited high antibacterial activities.