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. <b>66,</b> 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.
© 1997 Optical Society of America
Risto-Pekka Salmio, Jyrki Saarinen, Jari Turunen, and Ari Tervonen, "Graded-index diffractive structures fabricated by thermal ion exchange," Appl. Opt. 36, 2048-2057 (1997)