title: Graded-index diffractive structures fabricated by thermal ion exchange.
abstract: High-efficiency diffractive elements with a continuous phase-modulation capability can be realized either by means of a surface profile or a refractive-index distribution. We consider the latter approach, expanding on our recent proposal [Appl. Phys. Lett. 66, 917 (1995)] to fabricate graded-index diffractive structures by thermal ion exchange in glass. A rapid approximate method is developed to obtain a predesign of the ion-exchange mask, which is then refined by parametric optimization based on solutions of the full diffusion problem. The use of two consecutive ion-exchange steps and postbaking to enhance the designs is investigated, and some experimental results are provided.
authors.forename: R P
authors.initials: RP
authors.lastname: Salmio
authors.forename: J
authors.initials: J
authors.lastname: Saarinen
authors.forename: J
authors.initials: J
authors.lastname: Turunen
authors.forename: A
authors.initials: A
authors.lastname: Tervonen