Nanograting Bragg responses of femtosecond laser written optical waveguides in fused silica glass

Abstract

Multiple Bragg nanograting stop bands are reported for the first
\ntime in single and multi-mode optical waveguides generated by
\nfemtosecond laser direct writing in bulk fused silica glass. The stop bands
\nobserved in the guided broadband light spectra originated with the
\northogonal alignment of volume nanogratings co-generated with the
\nwaveguides. Rapid shifting of stop bands across the near UV and visible
\nspectrum was sensitively controlled by laser exposure and sample scanning
\ndirection. Bragg periods anticipated from the observed stop bands concurred
\nwith the nanograting structural pitches revealed by scanning electron
\nmicroscopy. The spectroscopic characterization of nanogratings along
\nmacroscopic-scale (12.5 mm long) waveguide sections constitutes a nondestructive,
\nconvenient and sensitive approach to examine long-range order
\nand uniformity of the self-organized periodic structures that may assist to
\nunravel the laser-glass interaction physics of nanograting formation.