Analysis of mode-field measurements using orthogonal polynomials

Mode-field measurements can be analyzed using a sum of orthogonal polynomials as the fitting function. This method is demonstrated theoretically and experimentally for the mode-field diameter (MFD) measurement of single-mode fibres using the transverse-offset (TO) technique. The fit error is reduced by an order of magnitude in comparison with an ordinary Gaussian fit, and is limited by instrumental noise. Using the Petermann 2 definition, expressions for the MFD and its estimated error are derived. The convergence of the method is demonstrated experimentally. It is shown that the MFD is independent of the chosen range of TO values. In the limit of a large range of equidistant X_i values, the orthogonal polynomials are Hermite-Gaussian polynomials. The transformation from TO field transmission coefficient to strip integrated far-field power can then be carried out easily, and the polynomial coefficients can be used for characterization of the field distribution     

Consensus prevention of crib death. CBO (Central Guidance Organization for Peer Review)

The sudden and unforeseen death of a child in the first two years, usually happening during a sleeping period, is known as cot death. As cot death is a very tragic and dramatic experience for the family, it is important to reduce its incidence. In the period between 1972 and 1987, the number of cot deaths initially increased, but during the last decade a substantial reduction could be observed. This fluctuation can be connected with the position in which the baby is put to sleep. From 1970 the prone sleeping position was strongly recommended. Since then, the number of cot death cases increased. From 1987, a causal relationship between the prone sleeping position and cot death was suspected. As a result the prone sleeping position was strongly advised against. A reduction of cot death cases was then observed. By now, the role of many other factors in cot death has been perceived. The risk of cot death is increased if these factors act at the same time. Some of these factors that promote cot death come from the child's environment and can be influenced when kept in mind. Apart from the prone or side sleeping position, heat congestion, unsafe bed material and smoking in the presence of the child substantially increase the risk of cot death. The main recommendations of the committee which drew up the Dutch consensus report on prevention of cot death are therefore aimed at avoiding the above mentioned risk factors. Continuation of research is necessary to further reduce the current number of some 50 cases of cot death which happen yearly in the Netherlands.