No abstract

No abstract

No abstract

A theoretical model of rare earth doped fiber amplifiers is presented, which takes into account the combined effects of modal structure of the fields propagating into the guide and dopant concentration distribution. From it the realistic evolution along the fiber of pump, signal and amplified spontaneous emission, local pump absorption and signal amplification coefficients, population inversion, spontaneous emission factor and amplifier noise figure can be obtained. The effectiveness of the model is demonstrated by analysing and discussing the performance of several fiber amplifiers.

There have been many discussions at conferences and in journals on the merits of various user-centered design (UCD) methodologies to address different types of design problems and how they fit into the design lifecycle. Generally, user-centered design professionals have promoted ethnographic work before the beginning of the design process, and iterative usability testing in the lab as the design progresses. Arguments for these UCD methods are well known to this community, and there is no question their adoption is a tremendous step forward over traditional software development approaches. However, we should guard against a too rigid division between ethnography and usability, and a too rigid sequence in practice, with ethnography only in the predesign phase, and laboratory usability testing as the sole UCD method later in design.In this article, we look at a situation that highlights potential limitations of this approach, one in which there were both a clear research need and a strong business case for a hybrid approach, integrating ethnography and usability throughout the development process. We call this approach "ethnographic field trials." In our experience, the arguments for such an approach and its costjustification are the strongest when introducing innovative technology. We will illustrate this with the example of a series of field trials we carried out over one and a half years to study three different iterations of the Microsoft Tablet PC prototype. We hope to follow up in subsequent articles with more detailed discussion of methodological issues and examples of ways in which the studies influenced the evolving design.