| This work is concerned, firstly, with the multiplexing of digital all-optical sensors for applications where the accuracy of the information required is not necessarily high, but where a large number of spatially distributed remote sensors may be required. Secondly, it is concerned with the possibilities of combining two independent signals, each carrying different types of traffic (e.g. communication data and sensing information) to form an integrated network. In response to the first aspect, a novel sensor network topology, which explores the similarities between digital sensor networks and data communication networks (such as LAN) is proposed. A network prototype has been constructed, evaluated, and the concept experimentally verified. It is demonstrated that this hierarchical multiplexing scheme facilitates the networking of a very large number of sensors, whilst employing low power sources and PIN photodetectors. The concept of signal quantization and subsequent optical digitisation is proposed for the design of digital sensors. For experimental verification of the concept two novel multi-bit, all-optical sensors, based on 'change of state', 'microbending', and Fabry-Perot principles, have been designed, constructed, and evaluated. These sensors are designed for temperature monitoring, but the general principle of signal quantization and digital encoding by optical sampling is equally valid for other types of measurands. Various time division multiplexed sensor array designs, based on multimode, single mode, and mixed fibre technologies have been evaluated and optimum solutions derived. The trade-offs between the maximum number of sensors, power requirements, and the required fibre delay lines are analysed, and families of solutions generated. For the second aspect of the work, three novel schemes (two involving systems integration in the optical domain, and one in the electrical domain via a computer gate way) are presented, and their validity tested by experimental demonstrations and theoretical evaluations. It is shown that two independent signals, each carrying different types of traffic, may be integrated to share a common path with negligible or acceptable penalties as a result of their mutual interaction. |
