Analysis and measurement of modal noise in an optical fibre

Modal noise in analogue and digital optical fibre systems has been demonstrated to be a significant effect. In this letter, we give some theoretical and experimental results concerning the behaviour of the signal-to-noise ratio in presence of modal noise considering the power from the exit face of a short sample of a graded-index multimode optical fibre.     

Generation of sequences of ultrashort pulses in erbium doped fibre single ring lasers

Active and passive mode locking has been observed in an erbium doped fibre single ring laser. Pulse durations as short as 100 fs at a repetition rate of 300 GHz have been measured from an erbium doped fibre amplification stage placed at the output of the fibre ring. The ultrafast regime depends critically on the dynamical evolution of the light polarisation along the cavity.<>     

Error proability in an atmospheric twin-channel optical link

The error probability for an atmospheric twin-channel optical link has been calculated for some conditions of signal scintillation and modulation depth. The results show that it is important to reduce the scintillation while it is unnecessary to use high modulation depths.     

3D phase-differentiated GDL microstructure generation with binder and PTFE distributions

In this work, a new framework and model for the digital generation and characterization of the microstructure of gas diffusion layer (GDL) materials with localized binder and polytetrafluoroethylene (PTFE) distributions were developed using 3D morphological imaging processing. This new generation technique closely mimics manufacturing processes and produces complete phase-differentiated (void, fiber, binder, and PTFE) digital 3D microstructures in a cost- and time-effective manner for the first time. The results for the digital generation of Toray TGP-H-060 with 5 and 0 wt.% PTFE were in close agreement with confocal laser scanning microscope (CLSM) images as well as 3D X-ray tomography studies. The resulting structure can be readily used for analyzing transport processes utilizing commercial CFD software.     

Error-rate measurements in an atmospheric twin-channel optical link

The error rate has been measured for an atmospheric twin-channel polarization modulated optical link in order to ascertain the applicability of a photon-counting digital model to the design of a simple realistic system. Error probabilities in the range10^{-2}-10^{-7}at 76 Mb/s were measured in different atmospheric conditions, for a path of 3.6 km. The agreement between experimental results and theoretical ones is satisfactory and justifies the use of the model in the design.     

Uneven gas diffusion layer intrusion in gas channel arrays of proton exchange membrane fuel cell and its effects on flow distribution

Intrusion of the gas diffusion layer (GDL) into gas channels due to fuel cell compression has a major impact on the gas flow distribution, fuel cell performance and durability. In this work, the effect of compression resulting in GDL intrusion in individual parallel PEMFC channels is investigated. The intrusion is determined using two methods: an optical measurement in both the in-plane and through-plane directions of GDL, as well as an analytical fluid flow model based on individual channel flow rate measurements. The intrusion measurements and estimates obtained from these methods agree well with each other. An uneven distribution of GDL intrusion into individual parallel channels is observed. A non-uniform compression force distribution derived from the clamping bolts causes a higher intrusion in the end channels. The heterogeneous GDL structure and physical properties may also contribute to the uneven GDL intrusion. As a result of uneven intrusion distribution, severe flow maldistribution and increased pressure drop have been observed. The intrusion data can be further used to determine the mechanical properties of GDL materials. Using the finite element analysis software program ANSYS, the Young's modulus of the GDL from these measurements is estimated to be 30.9 MPa.     

Brillouin gain curve dependence on frequency spectrum of PSK-modulated signals

The Brillouin gain curve in an optical fibre has been measured for various phase modulation formats as a function of the bit rate. Experimental results show that the gain can be obtained as the convolution of the intrinsic gain curve and the frequency spectrum of the modulated signal.<>     

Study on the Implementation of Optical Transparent Transport Networks in the European Environment—Results of the Research Project COST 239

Photonic Network Communications -     

Characterization of a O-fatty-acylated sulfatide from equine brain

A sulfatide, O-fatty-acylated 3-sulfogalactosylceramide at C6-O on galactoside, was isolated from equine brain and the chemical structure was characterized by proton NMR and MS. The O-acylation site of the acylated sulfatide was determined by the down-field shift of protons attached to a carbon having an O-acyl group in the NMR spectrum and by analysis of a partially methylated derivative before and after acetalization of the intact sulfatide using GC-MS. The O-acyl chain length was determined by GLC, revealing that it exclusively had palmitoyl and stearoyl residues as the major fatty acids. The enzymatic conversion to the O-acyl sulfatide was further examined using equine brain microsomes as an enzyme source and different lipid substrates, resulting in O-acylation of 3-sulfogalactosylceramide from stearoyl CoA, while 6-O-acyl galactosylceramide was not O-sulfated from phosphoadenosine phosphosulfate. The results were supported by the comparably different N-linked fatty acid components between two lipid substrates, in which the component of 6-O-acyl sulfatide was mostly similar to that of sulfatide, but not to 6-O-acyl galactosylceramide.