Integrated Optics: A New Focus for Inorganic Chemistry

Abstract

Photopatterning metal and/or metal oxides in porous, silica-based glasses and xerogels followed by thermal consolidation to a nonporous glass yields refractive index gradients that,depending on their shape, guide, focus, and defract light. The optical performance of these structures depends on the species photodeposited in the matrix, the changes they undergo during consolidation of the matrix, and their effect on the consolidating matrix. Gradient index structures derived from Fe(CO)₅ are composed of nanometer diameter metal and/or metal oxide particles, whereas those derived from (CH₃)₃SnI are composed of individual oxides or smaller aggregates within the SiO₂ matrix. Porous Vycor glass acts as a template for Fe^o-Fe₂O₃ particle growth during consolidation with the resulting gradient index structure consisting of 10±1 nm diameter particles composed of small aggregates of elemental iron dispersed in Fe₂O₃ with an average inter-particle spacing equivalent to the correlation length of the porous glass. Consolidation of the xerogel produces equivalent changes in refractive index and similar changes in the electronic spectra, but the gradient index is composed of a mixture of octahedrally and tetrahedrally coordinated Fe³⁺ present as individual molecular species, or as ≤1-nm diameter aggregates incorporated into the silica network. Photodeposition of tin offers a means to pattern porosity within a consolidated glass and a means to incorporate reagents unable to withstand the consolidation temperature of glass. Pattern resolution is limited by scattering of the photolyzing light by the SiO₂ nodules of the porous matrices, but thermal consolidation of the matrices occurs without loss of pattern resolution. Consistent with a random distribution of pores throughout these silica matrices, the change in pattern dimension on consolidation can be calculated from the void volume of the matrix. Various optical structures created by these photodeposition techniques and their optical performance are described.