N. Filonov and F. Klopp Absolutely continuous spectrum for the isotropic Maxwell operator with coefficients that are periodic in some directions and decay in other (229K, PDF) ABSTRACT. The purpose of this paper is to prove that the spectrum of an isotropic Maxwell operator with electric permittivity and magnetic permeability that are periodic along certain directions and tending to a constant super-exponentially fast in the remaining directions is purely absolutely continuous. The basic technical tools is a new ``operatorial'' identity relating the Maxwell operator to a vector-valued Schroedinger operator. This operator is then studied using a method developed by the authors in a previous paper.