Femtosecond laser micro/nano-machining of silica glass planar substrates for the production of Bragg gratings

Femtosecond laser pulses are increasingly utilized for the micro/nano-machining of a wide range of materials. They have been effectively employed in the production of fiber Bragg gratings (FBGs) through the implementation of point-by-point, line-by-line, and plane-by-plane processes. This study reports on the use of such lasers for the manufacture of Bragg gratings in pure fused silica planar substrates. In particular, the commercial system known as FEMTOprint was employed. This machine enabled the efficient production of Bragg gratings from bulk silica through several steps. Initially, a waveguide was engraved into the glass substrate through precise control of laser pulses and paths. Subsequently, an access point was created at one edge of the substrate to facilitate the easy connection of a standard optical fiber for light injection and collection. This was accomplished through the use of femtosecond laser pulses, followed by an etching process utilizing KOH to selectively ablate some material and create the necessary open spaces in the substrate. Finally, a third femtosecond laser process was utilized to inscribe a Bragg grating within the waveguide. The reflected amplitude spectrum of the grating was characterized with an FBG interrogator, and the obtained experimental results will be presented in this paper.