Matthias Fertig

Vector wave propagation method

In this paper, we extend the scalar wave propagation method (WPM) to vector fields. The WPM [Appl. Opt.32, 4984 (1993)] was introduced in order to overcome the major limitations of the beam propagation method (BPM). With the WPM, the range of application can be extended from the simulation of waveguides to simulation of other optical elements like lenses, prisms and gratings. In that reference it was demonstrated that the wave propagation scheme provides valid results for propagation angles up to 85 degrees and that it is not limited to small index variations in the axis of propagation. Here, we extend the WPM to three-dimensional vectorial fields (VWPMs) by considering the polarization dependent Fresnel coefficients for transmission in each propagation step. The continuity of the electric field is maintained in all three dimensions by an enhanced propagation vector and the transfer matrix. We verify the validity of the method by transmission through a prism and by comparison with the focal distribution from vectorial Debye theory. Furthermore, a two-dimensional grating is simulated and compared with the results from three-dimensional RCWA. Especially for 3D problems, the runtime of the VWPM exhibits special advantage over the RCWA.

Hybrid modelling for supervisory control purposes for the brine heater of a multi stage flash desalination plant

Multistage flash desalination is the most common process to produce freshwater from seawater based on large scale distillation. The process is energy intensive but essential for the maintenance of life support in regions with scarcity of water resources. Such plants need an efficient control system in order to be economically viable. A hybrid model for supervisory control purposes based of a hybrid automaton is proposed in this contribution.

Polarization-Independent Photodetectors With Enhanced Responsivity in a Standard Silicon-on-Insulator Complementary Metal–Oxide–Semiconductor Process

A polarization-independent photodetector device is demonstrated that can be combined with electronic integrated circuits on a single chip. The photodetector device is fully compatible with the standard silicon-on-insulator (SOI) complementary metal-oxide-semiconductor (CMOS) process without requiring process modification or postprocessing.

HYBRID SUPERVISORY CONTROL OF THE BRINE HEATER FOR MULTI STAGE FLASH DESALINATION PLANTS

Abstract Multistage Flash desalination is the most common process large-scale distillation process to produce freshwater from seawater. Its operation is energy intensive and essential for the maintenance of life support in regions with scarcity of water resources. Such plants need an efficient control system in order to be economically viable. Fortunately, the plant can be broken down into subsystems, where the brine heater has the function to increment the brine temperature to the saturation value. Temperature control of the brine is crucial for the overall stability and economy of plant operation. Here, an adaptive control system based on PID controllers supervised by a hybrid automaton is proposed for the brine temperature control loop.