Dichroic Bragg reflectors based on birefringent porous silicon

Multilayers of anisotropically nanostructured silicon (Si) have been fabric ated and studied by polarization-resolved reflection measurements. Alternat ing layers having different refractive indices exhibit additionally a stron g in-plane anisotropy of their refractive index (birefringence). Therefore, a stack of layers, acting as a distributed Bragg reflector, has two distin ct reflection bands, depending on the polarization of the incident linearly polarized light. This effect is governed by a three-dimensional (in-plane and in-depth) variation of the refractive index. These structures can yield optical effects which are difficult to achieve with conventional Bragg ref lectors. (C) 2001 American Institute of Physics.