Direct writing of Volume and Surface Gratings with Sub-micron Periods in Fused Silica.

Abstract

It is well established that ion implantation in silica glass increases the refractive index through compaction of the implanted material1. Another effect of the implantation is that color centers are created in great numbers, thereby enhancing the photosensitivity of the silica to ultraviolet light2. The compaction and color center generation are associated with damage in the material caused by the dissipation of a fraction of the incident ion energy into nuclear processes, the remainder of the energy being dissipated through ionization (i.e. electronic processes). In the work presented here, we demonstrate the use of a Focussed Ion Beam (FIB) facility for the direct writing of arbitrary grating patterns with sub-micron pitches. This technique was demonstrated before with an electron beam but only in chalcogenide glass thin films3. For comparison, we also present our results on grating formation in uniformly implanted silica glass by selective photobleaching of the induced color centers with ultraviolet light. Both these techniques may be compatible with the technology of doped silica-on-silicon for optical waveguide fabrication and will allow direct writing of sub-micron pitch grating filters in such photonic integrated circuits.