Enhancement of Brillouin Stokes generation in the S-band region using a combination S-band Depressed Cladding Erbium Doped Fiber and Semiconductor Optical Amplifier

A hybrid Depressed-Cladding Erbium Doped Fiber (DC-EDF) together with a broadband Semi-conductor Optical Amplifier (SOA) to enhance the generation of Stokes and anti-Stokes in a 7.7 km long Dispersion Compensating Fiber (DCF) is proposed and demonstrated. The performance of the proposed system is compared against that of a conventional system with only the DC-EDF as the gain medium, and the incorporation of the SOA can be seen to enhance the generation of Brillouin Stokes significantly. The proposed system is able to generate an output comb with a flat-top and more than 29 Stokes and 13 anti-Stokes lines, an increase of 14 and 8 lines respectively over the conventional system and covering the entire S-band region. The output comb generated is highly stable over time.     

Flat and compact switchable dual wavelength output at 1060 nm from ytterbium doped fiber laser with an AWG as a wavelength selector

A dual-wavelength ytterbium doped fiber laser with a narrowest spacing of 0.53 nm and widest spacing of 12.2 nm at 1064 nm is presented in this paper. An arrayed waveguide grating (AWG) together with an optical channel selector (OCS) have also been incorporated in the proposed setup that works as a switchable mechanism giving 23 different wavelength tunings. Producing an average output power of ?8 dB m and side mode suppression ratio (SMSR) of 59.65 dB, this dual-wavelength fiber laser is quite stable with an output power variance as low as 0.47 dB giving it an advantage due to its switching ability and stable dual-wavelength output powers.     

The hydrolytic degradation of a segmented glycolide-trimethylene carbonate copolymer (Maxon™)

The hydrolytic degradation of a segmented copolymer constituted by glycolide and trimethylene carbonate units (Maxon™) has been investigated by means of ¹H NMR spectroscopy and calorimetry. Degradation experiments have been performed either under a pH 7.4 buffered solution or in distilled water at temperatures of 37 and 50 °C. At both temperatures, the degradation proceeds through two main stages where an increase in the degree of crystallinity occurs in the first place. NMR peaks associated with glycolyl end units and appearing progressively can be well distinguished. Their chemical shifts coincide with those observed in the hydrolytic degradation of polyglycolide threads, which was also assayed for comparative purposes. Glycolide rings are also produced in a significant amount during the bulk degradation of Maxon. They are partially retained in the polymer, which may be a consequence of an intramolecular cyclization of the terminal hydroxyl groups.Thermal degradation in the presence of a transesterification catalyst has also been investigated and the changes in the polymer microstructure evaluated through the NMR analyses of signals were sensitive to the chemical sequence.     

Copolymerization of glycolide and trimethylene carbonate

The bulk ring‐opening copolymerization of glycolide with trimethylene carbonate was performed under different conditions. The influence of the composition, temperature, reaction time, and catalyst on the chain microstructure was studied by means of ¹H and ¹³C NMR spectroscopy. The final microstructure was found to be highly dependent on the transesterification reactions. The thermal behavior was sensitive to the composition and to the length of the glycolyl microblocks. Differential scanning calorimetry and X‐ray diffraction demonstrated that glycolyl‐rich sequences could give rise to a single crystalline phase, whereas trimethylene carbonyl units were incorporated into the amorphous phase. The synthesis of copolymers from the melt‐state transesterification of polyglycolide and poly(trimethylene carbonate) homopolymer mixtures was also studied. The hydrolytic degradation rate of the copolymers was found to depend on the microstructure and in general was enhanced with the degree of randomness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 993–1013, 2006     

Prevision des spectres de résonance magnétique nucléaire de 13C par intelligence artificielle: le problème de la codificationPrediction of 13C-nuclear magnetic resonance spectra by artificial intelligence: the problem of coding structures

Possible errors in earlier methods of coding structures are discussed, particularly with regard to α- and β-conformation and double bonds. The proposed method of coding is based on the absolute interatomic distances and the relative orientations of atoms. The coding system agrees with previous theoretical equations, except for density matrices; the usual classification of α, β and δ effects is obviously not included. An advantage of the method is that neighbouring atoms which have negligible effect are not included in the coding, so that the number of plausible structures is reduced. Another advantage is that similar structures can be tested, atom by atom, to a level at which complete structural equivalence no longer exists. The program developed on this basis is applicable with personal computers and provides options which enable the theoretical spectrum to be predicted, the signals to be interpreted if the experimental spectrum is known, and the influence of each neighbouring atom on the carbon signal to be studied.     

Operation of brillouin fiber laser in the O-band region as compared to that in the C-band region

A first time O band Brillouin fiber laser is demonstrated and compared with the C band Brillouin fiber laser. By utilizing a 20 km True wave fiber (TWF), the experiment demonstrated four Brillouin lines generated from the simple set-up of Brillouin fiber laser. We compared the threshold between the Brillouin pump wavelength at 1310 nm which represent O band region and 1550 nm for C band region. It shows that the Brillouin threshold at O band region is smaller that C band. The channels spacing between these two bands are also different, where O band have 12.72 GHz spacing while 1550 nm have 10.25 GHz spacing.     

Effect of PEO‐PPO‐PEO copolymer on the mechanical and thermal properties and morphological behavior of biodegradable poly (L‐lactic acid) (PLLA) and poly (butylene succinate‐co‐L‐lactate) (PBSL) blends

A blend of two biodegradable and semi‐crystalline polymers, poly (L‐lactic acid) (PLLA; 70 wt%) and poly (butylene succinate‐co‐L‐lactate) (PBSL; 30 wt%), was prepared in the presence of various polyethylene oxide‐polypropylene oxide‐polyethylene oxide (PEO‐PPO‐PEO) triblock copolymer contents (0.5, 1, 2 wt%). Mechanical, thermal properties, and Fourier transform infrared (FTIR) analysis of the blends were investigated. It was found that the addition of copolymer to PLLA/PBSL improved the fracture toughness of the blends as shown by mode I fracture energies. It was supported by morphological analysis where the brittle deformation behavior of PLLA changed to ductile deformation with the presence of elongated fibril structure in the blend with copolymer system. The glass transition temperature (T_g), melting temperature (T_m) of PLLA, and PBSL shift‐closed together indicated that some compatibility exists in the blends. In short, PEO‐PPO‐PEO could be used as compatibilizer to improve the toughness and compatibility of the PLLA/PBSL blends. Copyright © 2010 John Wiley & Sons, Ltd.     

Q-switched pulse generation from an all-fiber distributed Bragg reflector laser using graphene as saturable absorber

A Q-switched distributed Bragg reflector fiber laser using a graphene passive saturable absorber is proposed in a cavity consisting of a fiber Bragg grating and Faraday rotator mirror as end mirrors, together with a highly doped erbium-doped fiber as a gain source. The laser has a Q-switched threshold of about 28 mW and a tunable repetition rate of 10.4-18.0 kHz with varying pump power. The shortest pulse width obtained from the system is 3.7 its, with a maximum pulse energy and peak power of 22.2 nJ and 3.4 mW, respectively.     

Laser-diode-pumped zigzag oscillator power slab Nd：YAG master amplifier

A Q-switched distributed Bragg reflector fiber laser using a graphene passive saturable absorber is proposed in a cavity consisting of a fiber Bragg grating and Faraday rotator mirror as end mirrors, together with a highly doped erbium-doped fiber as a gain source. The laser has a Q-switched threshold of about 28 mW and a tunable repetition rate of 10.4-18.0 kHz with varying pump power. The shortest pulse width obtained from the system is 3.7 μs, with a maximum pulse energy and peak power of 22.2 nJ and 3.4 mW, respectively.     

Simultaneous determination of three organophosphorus pesticides in different food commodities by gas chromatography with mass spectrometry

A sensitive and selective gas chromatography with mass spectrometry method was developed for the simultaneous determination of three organophosphorus pesticides, namely, chlorpyrifos, malathion, and diazinon in three different food commodities (milk, apples, and drinking water) employing solid‐phase extraction for sample pretreatment. Pesticide extraction from different sample matrices was carried out on Chromabond C₁₈ cartridges using 3.0 mL of methanol and 3.0 mL of a mixture of dichloromethane/acetonitrile (1:1 v/v) as the eluting solvent. Analysis was carried out by gas chromatography coupled with mass spectrometry using selected‐ion monitoring mode. Good linear relationships were obtained in the range of 0.1–50 μg/L for chlorpyrifos, and 0.05–50 μg/L for both malathion and diazinon pesticides. Good repeatability and recoveries were obtained in the range of 78.54–86.73% for three pesticides under the optimized experimental conditions. The limit of detection ranged from 0.02 to 0.03 μg/L, and the limit of quantification ranged from 0.05 to 0.1 μg/L for all three pesticides. Finally, the developed method was successfully applied for the determination of three targeted pesticides in milk, apples, and drinking water samples each in triplicate. No pesticide was found in apple and milk samples, but chlorpyrifos was found in one drinking water sample below the quantification level.