Beams Propagation Modelled by Bi-filters

摘要

In acoustic, ultrasonic or electromagnetic propagation, crossed media are oftenmodelled by linear filters with complex gains in accordance with the Beer-Lambert law. Thispaper addresses the problem of propagation in media where polarization has to be taken intoaccount. Because waves are now bi-dimensional, an unique filter is not sufficient to represent theeffects of the medium. We propose a model which uses four linear invariant filters, which allowsto take into account exchanges between components of the field. We call it bi-filter because ithas two inputs and two outputs. Such a circuit can be fitted to light devices like polarizers,rotators and compensators and to propagation in free space. We give a generalization of theBeer-Lambert law which can be reduced to the usual one in some cases and which justifies theproposed model for propagation of electromagnetic beams in continuous media.