Abstract-We demonstrate a new device concept for wavelength division demultiplexing based on planar photonic crystal waveguides. The filtering of wavelength channels is realized by shifting the cutoff frequency of the fundamental photonic bandgap mode in consecutive sections of the waveguide. The shift is realized by modifying the size of the border holes. Simulations and an experimental realization of a four-channel coarse wavelength division demultiplexer are described.Index Terms-Photonic bandgap (PBG), photonic crystal (PhC) waveguide, wavelength-division multiplexing (WDM).
This paper considers the challenge of validating railway timetables and investigates how formal methods can be used for that. The paper presents a re-configurable, formal model which can be configured with a timetable for a railway network, properties of that network, and various timetabling parameters (such as station and line capacities, headways, and minimum running times) constraining the allowed train behaviour. The formal model describes the system behaviour of trains driving according to the given railway timetable. Model checking can then be used to check that driving according to the timetable does not lead to illegal system states. The method has successfully been applied to a real world case study: a time table for 12 trains at Naerumbanen in Denmark. Keywords: formal methods • model checking • UPPAAL • railways • timetables 1 Research in optimisation models and techniques for generating optimal timetables have been done [6], but these are very rarely used by the railway operators.
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