Abstract
The theory of two-dimensional (2-D) nonimaging concentrators is reviewed. A method for designing 2-D concentrators with inhomogeneous media, in which the refractive-index distribution is an output, is given. This method allows one to choose the shape of the mirrors when they are needed. As a result of the method we obtain a concentrator with maximum theoretical concentration formed by the composition of triangles of three different indices of refraction. The edge-ray principle is proven under several specific assumptions.